First Run with DS18B20 Temperature Sensor

I have a revised bedside fan (now with integrated LED illumination) up and running, and now it needs a temperature sensor. The goal is so I could automate turning off the fan once things cool down. My previous attempt used a TMP36 sensor that reported results as an analog voltage level. The results made me feel it was not a good fit with ESP8266 ADC peripheral. I don’t blame Espressif, it’s just a matter of different ADC designed for different usage requirements.

As an alternative to TMP36, I wanted to try a sensor that has its own integrated analog circuitry designed for the purpose and reported measurements via a digital communication protocol. Between what I could find in how-to guides and listed by vendors competing on price, I found my next candidate to be Maxim Semiconductor DS18B20 1-Wire Digital Thermometer. Another point in favor of this sensor is that it is frequently sold already packaged in a waterproof enclosure and a length of wire. This helps me place the sensor far enough away to avoid the heat generated by a running ESP8266. The lowest-bidder of the day sold them in a multipack of 15 (*) so that’s what I bought.

When I read through the DS18B20 datasheet, I was a little wary of its “1-Wire” data bus because I wasn’t sure I wanted to spend the time to implement another protocol. But I need not have worried: I only planned to use it with an ESP8266 running ESPHome, and somebody has already integrated the code to use these sensors.

The hardware side was simple: red wire to 3.3V, black wire to ground, and yellow wire to an ESP8266 pin. The only catch is that 1-Wire protocol requires a 4.7kΩ pull-up resistor so the chosen ESP8266 pin must be able to tolerate one. On my first try, I connected the data wire to Wemos D1 Mini pin D8 a.k.a. ESP8266 GPIO15 out of convenience. (It was easy to lay out on my circuit board.) Naturally Murphy’s Law ensured that I chose the pin that, if pulled high, would prevent an ESP8266 from booting. I had to move the data wire (and the pull-up resistor) to another pin before things would run. And now that it’s up and running, I think leveraging an Arduino library to read digital messages of DS18B20 measurement is preferable to using ESP8266 ADC to read TMP36 sensor voltage. Not to mention the convenience of having the sensor already encased and connected to a length of wire. This will be my go-to temperature sensor until I find a reason to try another.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Bedside Fan and Light V2

I took apart the Asiahorse Magic-i 120 V2 control hub and remote because I didn’t need them anymore: I could control its trio of fans with my own circuit board. How shall I wield such power? It was fun playing with 3D coordinate mapping with a Pixelblaze, but my most immediate need is a lot less exciting: combination bedside fan and light to replace my first bedside fan project. (Which didn’t have a light.)

For such a simple use, the power of a Pixelblaze is overkill. So, my board was modified to use an ESP8266 (Wemos D1 Mini module) as its brain, running ESPHome for integration with Home Assistant. In the Pixelblaze demo, the fans were always on. Now they will be controlled by that ESP8266 as well.

I’m still not settled enough on the idea to spend the time designing and 3D printing a proper frame, but at least I’ve put a bit more effort into this cardboard creation. I’m reusing a corner of a Newegg shipping box (I think it was the very box used to ship the Asiahorse fan bundle) and I’ve turned it inside out so at least I don’t have to stare at the Newegg logo every time I’m in bed.

Three large holes, one per fan, was cut from that cardboard for airflow. Twelve more holes, four per fan, were drilled into the cardboard for fan mounting screws. The physical assembly came together quickly, but there were a few more hiccups.

First problem was that FastLED, the addressable LED Arduino library used by ESPHome, is not compatible with the latest Arduino 3 framework at the time of this writing. Relevant ESPHome documentation page listed the issues as 1264 and 1322 filed against FastLED Github repository. Until they are resolved, ESPHome offers a workaround for compiling against Arduino framework 2.7.4. Which is what I did to run these WS2812 LEDs. For the first draft, I’m not going to use the addressable nature at all, just a single solid color. I think it would be cool to have a falling waterfall pattern on these lights, but that’ll be experimentation for later.

The second problem is that PWM control of fan speed results in an audible whine, probably an 1kHz whine which is the practical maximum speed for ESP8266 software PWM. The previous fan project removed the audible whine by adding a capacitor to smooth out voltage output. I could do that again, one capacitor per fan, but these fans run quietly enough at full speed I’m willing to skip PWM and have just on/off control.

The final problem is that I still want this fan to be responsive to temperature changes, turn itself off in the middle of the night when it got cool enough. I wasn’t happy with the TMP36 sensor I bought for the previous experiment, so now I’m going to try another sensor: the DS18B20.

RGB LED Fan Hub and Remote (Asiahorse Magic-i 120 V2)

I bought the Asiahorse Magic-i 120 V2 package from Newegg, which bundled three 120mm fans with embedded RGB LEDs with a hub and a remote to control those LEDs. Now that I have successfully created a control circuit for my own independent control of those fans and their LEDs, I no longer have any use for the hub and remote.

The remote has an array of 21 membrane buttons. Across the top, we can turn the LEDs “On” and “Off”. “Auto” will start running an animated pattern. Just below the “Off” button are brightness controls. S+ / S- controls the speed for animations, and M+ / M – cycles through different animated patterns. Bottom 12 buttons will show the selected solid color.

Top membrane is held on with moderately strong adhesive that could be peeled off, exposing the less interesting side of its circuit board.

Flipping the board over showed a single chip with its support components. There were no visible markings on the chip. Battery contact springs are at the bottom, the top features an infrared remote control LED emitter, and a few passive components in between.

After disassembling the remote, I started on the hub.

There were no exposed fasteners top or bottom. I pushed on the bottom sticker and felt the corners move.

The bottom sticker is glued on more tenaciously than the remote membrane keyboard and refused to come off cleanly. But at least those four Philips head fasteners are now exposed.

Not much to see on the bottom.

Flipping the circuit board over exposed… not many more chips than the remote. Most of the surface area are consumed by connectors all around the perimeter, and traces to connect them.

I’m glad to see fan connector pin labels are consistent with my reverse-engineered pinout table. A large component on this board appears to be a power transistor. I probed its pins and one of them is connected to all “F-” pins, so it is present for fan control. There are three sets of unused pads across the middle, provision for WS2812 LEDs wired in parallel with the fans. These three are chained together, left-to-right, with the leftmost LED receiving the same “DI” (data input) as all fans. When present, these three LEDs would act identically to first 3 out of 12 LEDs on board each fan.

There were a few other unpopulated pads on this circuit board, but there is one part I found fascinating for its absence: an infrared receiver like the one I found in a Roku. I don’t see one, and I don’t see solder pad provision for one. How could the hub receive IR remote signals without one? I know the remote and hub works together, so does this mean they communicate by radio frequency instead of infrared? I don’t know enough about RF circuits to look for components that would implement such a thing. I had thought all RF devices sold in the United States are required to have an FCC ID printed on it, but none are visible. Perhaps certain unlicensed frequency bands are exempt from FCC ID requirement? Shrug, doesn’t matter to me anymore as I won’t be needing this remote or hub to put their associated fans to use.

Orthogonal Fans with Pixelblaze 3D Mapping

I have built a control board for a trio of affordable PC case fans, replacing their bundled control hub of this Asiahorse Magic-i 120 V2 system. With my board I can control individual RGB LED inside these fans with help of a Pixelblaze LED controller. My initial tests used simple built-in linear patterns, but I wanted to use patterns that take advantage of 3D coordinate mapping. This is my favorite part of Pixelblaze and a core part of my Glow Flow project.

To get a 3D structure out of three fans, I did the easiest and most expedient thing: orient them orthogonal to each other with a few twist-ties. Now every fan motor axis lines up with one of three axes in 3D space. I have a Pixelblaze 3D coordinate test program already in hand, the RGB-XYZ 3D Sweep program I created during Glow Flow. All I had to do was create a 3D coordinate map in my Pixelblaze to describe LED layout in three-dimensional space.

I opened up the Pixelblaze mapping editor and… immediately got stuck. Where, exactly, should I map these LEDs? Physically, they are surface mounted on the central hub. However, their light diffused by translucent fan blade plastic, no longer fixed to a single location but distributed across entire fan diameter. Should I map the LEDs where they are physically? Or fan blade outer perimeter? Or somewhere in between? There really isn’t one single location for resulting output of a single LED.

I decided to experiment by writing my mapping code so a single variable controls how far from the center each location is. When pixelRadius is zero, everything is at the center and not very interesting. When set to 0.5, everything is mapped to the perimeter. I adjusted this value until the pattern “looked right” and that ended up at 0.4. I’m not satisfied with the empirical nature of this value, but I haven’t figured out a better way to account for diffusion.

Another problem with these LEDs is that they weren’t placed with precise coordinates in mind. I think LEDs were laid out on the circuit board relative to wiring bundle location, which is slightly offset from one of the four mounting arms. As a result, the LEDs aren’t aligned to any reference point on the exterior. To use an analog clock face as example, these LEDs are evenly placed but slightly offset from the hour numbers. Instead of lined up at 12, 1, 2, 3. They are at 12:10, 1:10, 2:10, etc.

These fans are physically squares with side lengths of 120mm. They can be installed in one of four orientations that are 90 degrees from each other and be mechanically fine. I usually choose my orientation based on whichever makes the wiring most convenient. But whatever the motivation, my 3D coordinate map would have to compensate for the resulting rotation.

The answer for both of the above rotation compensation concerns is an array fanRotationCorrection. One value for each fan, a sum of physical and LED offset rotations (in radians) added into coordinate map angle calculation for that fan.

Here is the result of my 3D pixel map running my RGB-XYZ sweep test program:

Here is my Pixelblaze Pixel Mapper code. [UPDATE: I later noticed that I got my Z-axis backwards. Be aware that both the video embedded in the tweet and this pixel mapper code are known to be flawed. At least they’re consistent with each other!]

function(pixelCount) {
  pixelPerFan = 12;
  pixelRadius = 0.4;
  fanRotationCorrection = [0.65, 0.65, 0.65];

  var map = [];
  for (i = 0; i < pixelCount; i++) {
    var ledNumber = i % pixelPerFan;
    var ledRadians = ((ledNumber/pixelPerFan) * Math.PI * 2);

    if (i < pixelPerFan) {
      ledRadians += Math.PI*fanRotationCorrection[0]
      map.push([0, 0.5 + Math.cos(ledRadians)*pixelRadius, 0.5 - Math.sin(ledRadians)*pixelRadius]);
    } else if (i < pixelPerFan*2) {
      ledRadians += Math.PI*fanRotationCorrection[1]
      map.push([0.5 - Math.cos(ledRadians)*pixelRadius, 0, 0.5 - Math.sin(ledRadians)*pixelRadius]);
    } else if (i < pixelPerFan*3) {
      ledRadians += Math.PI*fanRotationCorrection[2]
      map.push([0.5 - Math.cos(ledRadians)*pixelRadius, 0.5 + Math.sin(ledRadians)*pixelRadius, 0]);
    } else {
      // Unexpected pixels are placed at origin
      map.push(0,0,0);
    }
  }
  return map;
}

My Asiahorse investigation results were also posted to Pixelblaze forums. And now that I have full and complete control over these fans, I no longer need the hub that came in the box.

Control Board for Asiahorse 120mm Fans with RGB LED

I have a trio of PC cooling fans with embedded addressable RGB LED. They were designed to plug into a control hub that came in the bundle, but that hub had only a limited set of patterns and appeared to send the same signal to all fans. In order to run my own light show and control each fan individually, I determined the fan pinout and will now build my own control board for these fans.

The first problem was wiring. These fans came with a JST-PH style plug with 2.0mm pitch. (Distance between pins.) My perforated prototype circuit boards (and most connectors and components on hand) have a pitch of 0.1″ (~2.54mm) and would not fit. To work around this problem today, I cut off the factory connector and crimped on a replacement. These are JST-XH clones(*) with 0.1″ pitch. In the future, I might consider buying some perforated prototype boards with 2.0mm pitch (*) but that would have the problem of using components with 0.1″ pitch. The real solution is to make my own circuit boards that can accommodate whatever pitch I need, but that’s beyond my reach at the moment.

To generate individual control signals for these fans, I will be using the very awesome Pixelblaze controller. For power I will be using one of my salvaged 12V DC power bricks. It is rated for up to 1.5A which should be sufficient for a trio of fans and 12*3 = 36 LEDs. The barrel jack has a 5.5mm outer diameter and 2.1mm inner diameter, so I soldered a matching power jack (*) to the board. This will deliver power for the fans, with a decoupling capacitor to smooth things out. A buck converter (*) with convenient 5V preset feeds from that 12V rail to deliver 5V for Pixelblaze and LEDs.

I soldered some 2N2222A transistors for potential control of fan speed, but for this first iteration they’re pulled high so the fans spin all the time. It would have been easier to solder fan motor low wire directly to ground, but I have ambition of fan control in a future update.

The LEDs are connected in serial across all three fans. Pixelblaze data is connected to “data in” of the first fan, whose “data out” is connected to “data in” of the second fan, and onwards to the third fan. Configured for 12*3 = 36 WS2812-style LEDs, the Pixelblaze has individual control of every LED with a single data line. And for the first time, these three fans show patterns different from each other. With this new power I can make things even more interesting.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Pinout for Asiahorse 120mm Fan (Magic-i 120 V2)

The Asiahorse Magic-i 120 V2 bundle included three 120mm cooling fans with integrated addressable RGB LEDs. These fans have a six-wire connector designed to be plugged into a hub that was included in the bundle, along with a remote control to change the light shown performed by those LEDs. Most users just need to plug those fans into the included hub, but some users like myself want to bypass the hub and control each fan directly. For this audience, I present the fan connector pinout derived from an exploratory session on my electronics workbench.

Since this was reverse engineered without original design documents, I don’t know which side is considered “pin #1” by the engineers who designed this system. These connectors appear to be JST-PH, whose datasheet does point to one side as “Circuit #1”. But there’s no guarantee the engineers followed JST convention. To avoid potential confusion, I’ll call them only by name.

NameSystemComments
+12VFanHigh side of fan motor. Hub connects this wire directly to +12V power input.
Motor LowFanLow side of fan motor. Use a power transistor between this wire and ground to control fan speed.
GroundFan + LEDPower return for LED circuit and can be used for fan motor low side as well. Hub connects this wire directly to power input ground.
Data InLEDInput control signal for addressable RGB LED. Compatible with WS2812/”NeoPixel” protocol.
+5VLEDPower for LED circuit. Hub connects this wire directly to +5V power input.
Data OutLEDControl signal for addressable RGB LED beyond the end of LED string inside the fan. Useful for chaining multiple units together by connecting this wire to Data In of the next device in line.

Now that I understand its pinout, I will build my own control circuit to replace the default Asiahorse hub.

Exploring 6-Wire Connector of Asiahorse Magic-i 120 V2

I was curious about PC accessories with embedded addressable RGB LED, so I bought the cheapest item available on Newegg that day. I have verified it works as originally intended, and now I’m going to dig deeper. This Asiahorse Magic-i 120 V2 is a three-pack of 120mm fans with integrated LEDs. All three fans plug into a hub that has a corresponding remote control for me to select from a list of programmed patterns. This bundle is fine if I’m satisfied with those patterns, but I want display patterns of my own.

Each fan connects to the hub through this six-wire connector. The distance between each pin is 2mm. Judging by the pitch and physical appearance, I guess they are JST-PH or a clone. (I don’t have any 6-conductor JST-PH to verify.) This is mildly inconvenient because my workbench is setup to work with 0.1″ pitch (~2.54mm) connectors so it’s not very easy for me to probe those signals as-is.

The solution is a quick soldering project to give me an exploration board. I cut the bundle of six wires and inserted a small piece of perforated prototype board. Each of the six wires are then bridged with an exposed length of solid wire, easy for me to clip probes onto.

Trying the easy thing first, I probed for continuity between these six wires and the power input wires. This gave me location for +12V source, +5V source, and ground. Armed with this information, I soldered capacitors to smooth out both power rails, because the AC adapter I’m using is designed for far higher wattage than a few LEDs and it’s not unusual for switching power supplies to be noisy at low power levels. (And the cheap ones are always noisy at all power levels…)

With three out of six wires identified for power, this left me with three more wires to decipher. Here are my candidates:

  • Fan control: it may be one (or none) of the following:
    • Fan motor high side: the fan may be internally connected to the ground wire, and the high side wire is left exposed here for external PWM or on/off control with a power transistor.
    • Fan motor low side: the same idea but reverse: fan motor is internally connected to +12V and the low side is exposed here for external PWM or on/off control with a power transistor.
    • Fan motor PWM: Neither of the above. Instead of leaving either high or low side unconnected for external power transistor, a suitable power transistor is built into the fan and controlled with a 25kHz PWM signal as used in 4-wire fans.
  • Fan tachometer like the type I found in 3-wire fans.
  • LED Data In: addressable RGB signal input.
  • LED Data Out: signal that has passed through the LED string inside this device and ready to be passed on to other LEDs in other devices down the chain.

To decipher which wires are which of those candidate capabilities, I connected my Saleae Logic 8 to the three unknown wires. I started an analog waveform capture session and used the fan remote control to command that all fans show a solid green.

The top line in white stayed at 0V through the entire session. This may be the tachometer wire, or it may be fan motor low side. To determine which, I disconnected everything other than the +12V and ground wires. The fan did not move. I connected the wire corresponding to this white line to ground, and the fan started spinning. Conclusion: this wire is fan motor low side.

The middle line in brown shows a distinct repeating pattern. The bottom line in red shows the same repeating pattern, but delayed by 12 cycles. Since there are 12 LEDs in a fan, that means the middle brown line is LED Data In and the red line is LED Data Out.

To verify LED Data In, I connected +5V, ground, plus this wire to the data pin of a Pixelblaze. After I configured the Pixelblaze to emit control signal for a string of 12 x WS2812 (NeoPixel) LEDs, I saw them light up appropriately on the fan.

To verify LED Data Out, I connected it to the data input pin of an array of 64 WS2812 LEDs. I configured the Pixelblaze for 12 + 64 = 76 pixels. After colorful pixels cycle through the fan, they marched onwards to the array as appropriate for LED Data Out.

With these functions verified, I’m confident enough to describe this Asiahorse fan pinout.

Asiahorse Magic-i 120 V2

I wanted to play with a set of PC case cooling fans with embedded addressable RGB LEDs, with the intent of learning how to control them for a future project. For extra challenge, I got a multipack that combined both fan and LED controls into a single (probably proprietary) connector that plugged into a bundled hub. Using the selection criteria of “Lowest bidder of the day” I bought a three-pack of fans: the Asiahorse Magic-i 120 V2 and I look forward to seeing how it works.

Before I start cutting things up, I need to verify the product worked as originally designed. I won’t need a computer for this as this multipack came with a remote control for the hub that allows operation without a computer. This lets me explore its signals without the risk of damaging a computer. I just need to supply power in the 4-pin accessory format popular with pre-SATA hard drives and optical disks. I didn’t need a computer here, either, as I had an AC adapter with this plug that originally came in a kit that turned internal HDDs into USB HDDs.

There were no instructions in the box, but things were straightforward. Three fans plugged into the hub, and a power cable connected my AC adapter to the hub. As soon as I turned on the power, all three fans started spinning. The LED light show didn’t start until I pressed the “On” button on the remote.

RGB LEDs in this fan are mounted in the hub, on the outside perimeter of the motor control board. I count 12 LEDs and they aimed along motor axis upwards into the center portion of translucent fan blades. These colorful lights are then diffused along length of the blade, resulting in a colorful spinning disk. While shopping on Newegg I saw other arrangements. Some fans have LEDs around the outside perimeter instead, and some fans illuminate both the hub and the perimeter. Each manufacturer hoping to capture the attention of a buyer with novelty of their aesthetic.

This remote control allowed me to cycle between various colorful programs or choose from a set of solid colors. I had hoped the colorful programs would ripple across the fans, but all three fans appear to display identical light sequence. I could control LED brightness or turn all the lights off, but I didn’t seem to have any control over fan speed. I guess this is where an instruction manual would have been useful.

If I wanted to build something bright and colorful that circulates air, almost everything is already here and ready to go. I just have to wire up a power switch to turn everything on/off, and the remote can take care of the rest. But I didn’t buy this just to have some lights. I wanted full control and I’m not afraid to start cutting things up to get there.

Shopping for PC Cooling Fans with RGB LED

I’ve decided to investigate controlling the RGB LEDs embedded in aesthetics-based PC accessories. I’m not interested in using them for my PC, but as research for a yet to be determined future electronics project. I wanted something that is a standardized commodity with a large range of variety in the ecosystem and have some usefulness beyond just looking shiny. I settled on 120mm PC cooling fans.

There are many common sizes for cooling fans, but I’ve found 120mm to be the most common for aftermarket cooling. They’re larger than average for CPU cooling, but not too large especially for heat-pipe based cooling towers. But they’re typically installed for general cooling in tower cases, whose cooling vents are cut for 120mm fans. Covering both popular use cases mean more options.

Looking around on my NewEgg, I find that fans sold individually typically have two separate connectors. One for LED and one for fan control. To the rest of the computer, these fans look like two separate peripherals: the LED and the fan. They just happened to coexist in the same device. The fan control connector sometimes just have two wires for +12V and ground. Some have a third tachometer wire for reporting speed, and some have a fourth wire for built-in PWM control. Here’s an example of a CPU cooler the Vetroo V5 whose fan has two connectors: a 4-pin CPU cooler fan control connector and a JRAINBOW RGB LED plug. These should be simple and straightforward to interface.

More challenging are fans that use an intermediate hub. The hub has a connector for power and for JRAINBOW, consolidating those signals into a proprietary connector. I started contemplating this particular Rosewill RGBF-S12001 three-pack of fans which use such a design. I think I can decipher roles of each wire so I could bypass the hub and control each fan directly. This multipack also had a remote control for direct control of the hub without a computer. This is appealing to me, because independent control meant I didn’t need a PC involved as I probed how it worked. If I should make a fatal mistake (say, accidentally short-circuited something) it should only kill the hub or the fan and not an entire computer.

As I scrolled down, though, Newegg showed me several other items under “similar products”. I saw an even more discounted three-pack of fans: the Asiahorse Magic-i 120 V2. Three fans for fourteen bucks, well within my impulse buy range. I’ll buy the pack and see what it does.

Repurposing PC RGB LED Accessories

I’m quite comfortable poking around inside the tower case of a DIY PC. I’ve built a few PCs from components, and I’ve bought a few that came prebuilt by a shop. In my PC experience I’ve focused on the functional side of things and haven’t paid much attention to the aesthetics side. There’s a whole segment of the market enchanted with flashy LEDs. As an electronics hobbyist, it had been hard for me to look at those accessories seriously. I know how little addressable RGB LED modules cost in bulk, and it is quite clear those PC accessories were sold at a huge profit margin. I would be more inclined to build my own LED creations like Glow Flow than to pay a premium just for overpriced flashy lights in my PC.

But what if I looked beyond products’ MSRP? Since this particular market is about novelty, just like the clothing fashion industry there is a high turnover of products. The huge profit margin entices startups hoping to make it big, and most don’t. High product turnover means there are those who upgrade to the latest look. Each of these scenarios can lead to products sold well below MSRP: (1) clearance sales on unsold inventory of “old looks” (2) liquidation sales from bankrupt companies, and (3) secondhand markets (eBay/Craigslist) for those who have upgraded. A bargain hunter can find LED-bedazzled gear well below the price of new equipment, and in extreme cases even lower than price of buying new WS2812 modules directly.

Well, now I’m interested! Not for my PC, but for potential future electronics projects. Which means looking at these products and try to figure out how I can repurpose them. I started by looking at the product pages for a few PC hardware component companies and their advertising spiel for RGB LED accessories.

  • Corsair uses the iCUE branding as an umbrella covering aesthetics-based accessories. Some are the addressable LEDs I care about, but not all of them.
  • Gigabyte uses the name RGB Fusion.
  • Asus calls theirs Aura.
  • MSI calls theirs Mystic Light.

I hit a gold mine on MSI’s Mystic Light site, because their FAQ included an entry “What is Mystic Light Extension” that gave the following description:

Mystic Light Extension is a feature of Mystic Light software which allows user to control colors and effects of partner’s product such as RGB LED Strips, RGB PC Fans or RGB PC Case via on-board JRGB / JRainbow / JCorsair pin header.

    JRGB (4-Pin / PIN-definition: 12V/G/R/B): The JRGB pin header provides up to 3A (12V) power supply for non-addressable 5050 RGB LED solution showing single color.
    JRAINBOW (3-Pin / PIN-definition: 5V/D/-/G): The JRainbow pin header provides up to 3A (5V) power supply for addressable WS2812 RGB LED (ARGB) solution showing rainbow color.
    JCORSAIR (3-Pin / PIN-definition: 5V/D/G): The JCorsair pin header provides up to 3A (5V) power supply to Mystic Light software compatible CORSAIR devices.

This tells me products that use the JRGB header are colorful but not individually addressable. Products using JRAINBOW or JCORSAIR are 5V devices that uses a single data pin and no clock. This is a very strong hint these products are made of LEDs made of either WS2812 (“NeoPixel”) or alternatives that understand the same control signals. I will go look for a bargain and try one out.

Temperature Responsive Cereal Box Fan

This quick and easy project produces a quiet breeze for hot summer nights. I wanted something gentler than the fans already in the house, and I wanted it to automatically turn itself off in the middle of the night once things cooled down enough. It also let me apply lessons I’ve recently learned. Even though I’ve found that the TMP36 sensor isn’t a great fit for a ESP8266, it’s something already on hand for an ESP8266 to tell if it’s cool enough to turn the fan off.

The 3-wire fan is a PC cooling fan with a 200mm diameter, relatively large within that category. I bought it some years ago for my first Luggable PC project, it was just a bit too large for that purpose and sat idle until now. I thought about designing and 3D-printing a stand for this fan, but in the spirit of keeping things simple and quick, I mounted it in an empty cereal box instead. Cutting holes in the box to accommodate the fan took a tiny fraction of the time it would have taken to 3D-print something.

Primary air intake was the top of the box, left open.

I cut a smaller secondary air intake towards the bottom of the box, which also makes it easy to toss my control board in there and feed it power from a salvaged DC power supply. A TMP36 sensor was soldered in the farthest corner in this picture, visible sticking up vertically.

Results

Running ESPHome (YAML excerpt below) this project successfully controls fan speed via ESP8266 PWM. It was also able to read temperature via TMP36 sensor, but values were affected by ESP8266. Located 1/2 of the circuit board away plus the entire height of its legs was not enough distance from the ESP8266 heat island: temperature reading dropped noticeably whenever the fan is turning. Still, it’s enough for me to create a Home Assistant automation to turn off this fan whenever the temperature dropped below a certain threshold. Due to the heating from ESP8266, the temperature value rises a few degrees immediately after the fan was turned off. Thankfully there was no risk of system feedback oscillation, because I did not create an automation to turn the fan on — I do that manually when I’m ready for a light breeze.

This worked well sitting on my bedstand, creating a light cool breeze when I’m ready to fall asleep and turning itself off while I was asleep. But its physical footprint was a problem: it took up space that is ideally used for a bedstand light. The obvious solution was to pull some LEDs into the next version, which is an opportunity to tackle another item on my to-learn list: PC accessories with embedded RGB LEDs.


ESPHome YAML to read TMP36 temperature and fan speed every 5 minutes:

sensor:
  - platform: adc
    pin: A0
    name: "Fan Temperature"
    unit_of_measurement: "°C"
    update_interval: 1s
    accuracy_decimals: 2
    filters:
      - multiply: 100
      - offset: -50
      - sliding_window_moving_average:
          window_size: 450
          send_every: 300
          send_first_at: 15
  - platform: pulse_counter
    pin: 12
    id: fan_rpm_counter
    name: "Fan RPM"
    unit_of_measurement: "RPM"
    accuracy_decimals: 0
    update_interval: 300s
    filters:
      - multiply: 0.5 # 2 pulses per revolution

output:
  - platform: esp8266_pwm
    pin: 14
    id: fan_pwm_output
    frequency: 1000 Hz

fan:
  - platform: speed
    output: fan_pwm_output
    id: fan_speed
    name: "Fan Speed Control"

TMP36 Temperature Sensor + ESP8266 = Not a Great Team

After successfully building a small circuit for 3-pin fan PWM control, I decided to add a temperature sensor. Now I have the option to make it smarter about adjusting speed (or stopping entirely) based on temperature. There are many temperatures sensor options, I decided to start simply and inexpensively with a sensor that returns an analog voltage representing temperature. A batch of TMP36 (*) seemed like a good starting point.

According to the Analog Devices datasheet, TMP36 output pin voltage is 0.75V at 25 degrees Celsius. For every degree of temperature rise, voltage increases 0.01V. For my first draft I wired it to my Wemos D1 Mini module’s analog input pin. But I had to adjust the scaling because a D1 Mini includes a voltage divider to scale input of 0-3.3V down to ESP8266 ADC range of 0-1V. This voltage divider (and math necessary to convert it back) added error to the reading. Since I intend to use this sensor for measuring room temperature, I do not expect to measure above 50 degrees Celsius (122 Farenheit) which corresponded to 1 Volt. Thus, I soldered a wire to connect TMP36 signal directly to ESP8266 module analog input, bypassing the voltage divider.

I noticed that there appears to be a startup time period where the temperature reading is 2-3 degrees too high but, after about 5-10 minutes, it will drop to a steady state temperature and stay there. I’m not sure if this startup behavior is from the TMP36 sensor or from the ESP8266 ADC. Either way, it meant I could not use this sensor in a sleep/read/sleep/read cycle because such a quick read will always result in a too-high value from this startup behavior.

With the initial breadboard test complete, I built a dedicated temperature sensor node with just an ESP8266 with a TMP36. In the interest of compactness, I decided to solder the sensor directly to ESP8266 module pins.

Upon startup, I saw that it reported temperature that was a few degrees too high, but I thought that was just the startup behavior I already noticed. But instead of dropping, it had kept going up. I thought I had a bad TMP36 until I realized it was accurately reading heat generated by a running ESP8266. According to my USB power meter, it consumed less than a third of a Watt, but that’s plenty of heat for a directly-mounted TMP36 to pick up.

If I wanted to measure a room’s air temperature and not temperature of a running ESP8266, I needed to give the sensor some distance. But even then, the readings weren’t reliable.

A little web research taught me that the ESP8266 ADC isn’t very precise nor is it calibrated. For most applications, being off by a few hundredth of a volt is a negligible error, but here every hundredth of a volt represents an entire degree of temperature which is decidedly not negligible. Taking multiple values and averaging them did help with the precision, but not accuracy. Knowing what I know now, in hindsight I should have done this with an ESP32. Those chips (or at least newer units) have their ADCs calibrated at Espressif factory. Though it is more likely that I will try a different temperature sensor in a future project. Either way, right now I have TMP36 on hand with a circuit board suitable for controlling 3-wire PC cooling fans. Time to put them together to do something useful.


Even though it doesn’t work very well, here’s an ESPHome YAML excerpt anyway. This will read a TMP36 every second and report average value every five minutes. TMP36 signal is assumed to have been soldered directly to ESP8266 analog input, bypassing Wemos D1 Mini voltage divider.

sensor:
  - platform: adc
    pin: A0
    name: "Mobile Node Temperature"
    unit_of_measurement: "°C"
    update_interval: 1s
    accuracy_decimals: 2
    filters:
      - multiply: 100
      - offset: -50
      - sliding_window_moving_average:
          window_size: 450
          send_every: 300
          send_first_at: 15

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

High-Side Fan ESP8266 PWM Using Optocoupler

It was neat that I could control the speed of a 4-wire CPU cooling fan with just software a PWM signal from an ESP8266, but 4-pin fans with built-in power switching are in the minority. Most available fans have no built-in speed control and depend on external PWM circuitry to vary their input voltage level. If I wanted to control speed of such fans with an ESP8266, I’ll need to get a power transistor of some sort into the circuit.

I’ve found several tutorials online for fan speed control via PWM, but they all use a transistor on low side of the fan. They do this because it makes the circuit easier. We connect the black fan wire to collector of the transistor, connect emitter to ground, and finally connect PWM signal from our microcontroller to transistor base. This will work because the transistor and the microcontroller share a common ground. A transistor needs only a volt or so on the base pin, easily delivered from any microcontroller.

The problem with this approach is that we could no longer directly read the tachometer signal of 3-pin fans, because they are open-drain to the “ground” which is no longer ground but low side of the fan. Depending on implementation details on the fan, the voltage level on that pin may rise too high for the microcontroller.

There are many valid ways to resolve this situation, the path I chose is to use a PC817 optocoupler. (*) Internally it is a LED pointed at a receiver. This optical system transmits a signal while electrically separating LED side from receiver side. In my case this I no longer need a common ground.

From here, there are two options forward: I could use the optocoupler to read the tachometer signals, or I could use the optocoupler to put the transistor on the fan’s high side. I chose to switch the fan’s high side so the fan has a common ground with the microcontroller, and I could directly read tachometer signal. Of course, it is valid to use optocoupler on both motor power PWM and for tachometer feedback. This is necessary for electrically noisy motor systems, but the brushless fan of a computer cooling fan (usually) does not require such measures.

I did have to add a capacitor to smooth out my PWM output, but that would have been necessary in any case. Having full PWM control means I can now switch the fan off completely with a 0% duty cycle, but it also means I am responsible for avoiding low PWM levels where a fan could not turn and stalls. After I proved I had PWM control via Home Assistant UI, I thought it would be fun to have the option to control fan based on temperature, so I added a TMP36 sensor.


ESPHome YAML excerpt for basic PWM fan control and reading fan tachometer. Note: this simple example lacks intelligence to avoid low PWM levels that would stall a fan.

sensor:
  - platform: pulse_counter
    pin: 12
    id: fan_rpm_counter
    name: "Fan RPM"
    unit_of_measurement: "RPM"
    accuracy_decimals: 0
    update_interval: 300s
    filters:
      - multiply: 0.5 # 2 pulses per revolution

output:
  - platform: esp8266_pwm
    pin: 14
    id: fan_pwm_output
    frequency: 1000 Hz

fan:
  - platform: speed
    output: fan_pwm_output
    id: fan_speed
    name: "Fan Speed Control"

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

ESP8266 Controlling 4-Wire CPU Cooling Fan

I got curious about how the 4 wires of a CPU cooling fan interfaced with a PC motherboard. After reading the specification, I decided to get hands-on.

I dug up several retired 4-wire CPU fans I had kept. All of these were in-box coolers bundled with various Intel CPUs. And despite the common shape and Intel brand sticker, they were made by three different companies listed at the bottom line of each label: Nidec, Delta, and Foxconn.

I will use an ESP8266 to control these fans running ESPHome, because all relevant code has already been built and ready to go:

  • Tachometer output can be read with the pulse counter peripheral. Though I do have to divide by two (multiply by 0.5) because the spec said there are two pulses per fan revolution.
  • The ESP8266 PWM peripheral is a software implementation with a maximum usable frequency of roughly 1kHz, slower than specified requirement. If this is insufficient, I can upgrade to an ESP32 which has hardware PWM peripheral capable of running 25kHz.
  • Finally, a PWM fan speed control component, so I can change PWM duty cycle from HomeAssistant web UI.

One upside of the PWM MOSFET built into the fan is that I don’t have to wire one up in my test circuit. The fan header pins were wired as follows:

  1. Black wire to circuit ground.
  2. Yellow wire to +12V power supply.
  3. Green wire is tachometer output. Connected to a 1kΩ pull-up resistor and GPIO12. (D6 on a Wemos D1 Mini.)
  4. Blue wire is PWM control input. Connected to a 1kΩ current-limiting resistor and GPIO14. (D5 on Wemos D1 Mini.)

ESPHome YAML excerpt:

sensor:
  - platform: pulse_counter
    pin: 12
    id: fan_rpm_counter
    name: "Fan RPM"
    update_interval: 5s
    filters:
      - multiply: 0.5 # 2 pulses per revolution

output:
  - platform: esp8266_pwm
    pin: 14
    id: fan_pwm_output
    frequency: 1000 Hz

fan:
  - platform: speed
    output: fan_pwm_output
    id: fan_speed
    name: "Fan Speed Control"

Experimental observations:

  • I was not able to turn off any of these fans with a 0% duty cycle. (Emulating pulling PWM pin low.) All three kept spinning.
  • The Nidec fan ignored my PWM signal, presumably because 1 kHz PWM was well outside the specified 25kHz. It acted the same as when the PWM line was left floating.
  • The Delta fan spun slowed linearly down to roughly 35% duty cycle and was roughly 30% of full speed. Below that duty cycle, it remained at 30% of full speed.
  • The Foxconn fan spun down to roughly 25% duty cycle and was roughly 50% of the speed. I thought it was interesting that this fan responded to a wider range of PWM duty cycles but translated that to a narrower range of actual fan speeds. Furthermore, 100% duty cycle was not actually the maximum speed of this fan. Upon initial power up, this fan would spin up to a very high speed (judged by its sound) before settling down to a significantly slower speed that it treated as “100% duty cycle” speed. Was this intended as some sort of “blow out dust” cleaning cycle?
  • These are not closed-loop feedback devices trying to maintain a target speed. If I set 50% duty cycle and started reducing power supply voltage below 12V, the fan controller will not compensate. Fan speed will drop alongside voltage.

Playing with these 4-pin fans were fun, but majority of cooling fans in this market do not have built-in power transistors for PWM control. I went back to learn how to control those fans.

CPU Cooling 4-Wire Fan

Building a PC from parts includes keeping cooling in mind. It started out very simple: every cooling fan had two wires, one red and one black. Put +12V on the red wire, connect black go ground, done. Then things got more complex. Earlier I poked around with a fan that had a third wire, which proved to be a tachometer wire for reading current fan speed. The obvious follow-up is to examine cooling fans with four wires. I first saw this with CPU cooling fans and, as a PC builder, all I had to know was how to plug it in the correct orientation. But now as an electronics tinkerer I want to know more details about what those wires do.

A little research found the four-wire fan system was something Intel devised. Several sources cited URLs on http://FormFactors.org which redirects to Intel’s documentation site. Annoyingly, Intel does not make the files publicly available, blocking it with a registered login screen. I registered for a free account, and it still denied me access. (The checkmark next to the user icon means I’ve registered and signed in.)

Quite unsatisfying. But even if I can’t get the document from official source, there are unofficial copies floating around on the web. I found one such copy, which I am not going to link to because the site liberally slathered the PDF with advertisements and that annoys me. Here is the information on the title page which will help you find your own copy. Perhaps even a more updated revision!

4-Wire Pulse Width Modulation
(PWM) Controlled Fans
Specification
September 2005
Revision 1.3

Reading through the specification, I learned that the four-wire standard is backwards compatible with three-wire fans as those three wires are the same: GND, +12V supply, and tachometer output. The new wire is for a PWM control signal input. Superficially, this seems very similar to controlling fan speed by PWM modulating the +12V supply, except now the power supply stays fixed at +12V and the PWM MOSFET is built into the fan. How is this better? What real-world problems are solved by using an internal PWM MOSFET? The spec did not explain.

According to spec, the PWM control signal should be running at 25kHz. Fan manufacturers can specify a minimum duty cycle. Fan speed for duty cycle less than the minimum is open for interpretation by different implementations. Some choose to ignore lower duty cycles and stay running at minimum, some interpret it as a shutoff signal. The spec forbids pull-up or pull-down resistor on the PWM signal line external to the fan, but internal to the fan there is a pull-up resistor. I interpret this to mean that if the PWM line is left floating, it will be pulled up to emulate 100% duty cycle PWM.

Reading the specification gave me the theory of operation for this system, now it’s time to play with some of these fans to see how they behave in practice.

FormLabs Form 1+ Galvanometer Power Failure

I tried to revive a FormLabs Form 1+ resin printer that had been sitting unused for years, but the test print was a failure. Comparing against videos on YouTube showing a Form 1/1+ in action, I noticed two differences. First, the resin vat tilting action (to peel it off a print between layers) was not happening. And more seriously, the laser beam was not moving around to trace out the shape. Instead, it stayed focused on one spot solidifying resin and damaging the resin vat at that point. There are four mechanical actuators on this device: the vat tilt stepper motor, X/Y-axis galvanometers (shortened below to galvos), and the Z-axis stepper motor. Out of four, three aren’t working! Quite disappointing, but at least they should be electromechanical issues that I have a better chance of fixing than software issues. I’ll take it apart and look around.

My disassembly was guided by Bunny Studios’ Form 1 teardown blog post from almost ten years ago. I was glad for the reference, but as the blog post pointed out, FormLabs designed the machine for easy disassembly, inspection, and repair. All fasteners are easily accessible and use the same 2.5mm hex key.

Once I got to remove the back panel, majority of control circuitry became accessible. Only one circuit board is not visible in this picture, as it is mounted in the front for power button and screen.

The large horizontal circuit board has a power-handling section to the right, as indicated by the presence of many transistors, diodes, and inductors. To the left is the brain, including a SanDisk 4GB SD card that wasn’t accessible until the back panel was removed. The smaller vertical circuit board on the right is dedicated to X/Y position control, judging by cables connecting it to the X/Y galvos.

This printer had been shipped around without its original packaging materials, so I had hoped the problem was as easy as a loose connector I could plug back in. Thus my attention was immediately drawn to headers on these circuit board without a wire, but there were no candidate loose wires to plug into those headers. Apparently FormLabs has intentionally chosen not to use those connections, likely related to changes from original Form 1 to this Form 1+.

One of the unused connectors was labeled GALVO Y POWER. I see cables on GALVO Y SIGNAL and GALVO X SIGNAL as well as GALVO X POWER. I guess both galvos are powered from GALVO X POWER cable. This might be relevant to what I find later.

Disappointed that I didn’t find a loose connector I could plug back in or any other obvious easy-to-fix problems, I proceeded to unplug and reinstall every connector to reseat them. Working from left-to-right, everything looked and felt fine until I unplugged the right-most galvo connector. Once it was removed, I got a clear view of the galvo power connector below it.

Discoloration from overheating and possibly soot from a small fire. The toasty connector is the other end of GALVO X POWER. I don’t know enough about this device to say sharing X and Y galvo power from a single connector caused the failure, but it certainly looks suspicious.

I saw no obvious places where GALVO Y POWER could have connected to this galvo control board. I guess it is a later revision that integrated both galvo controls on a single board powered by a single cable. Compare this to Bunny’s earlier device, where we see two separate and seemingly identical galvo control boards, one for X and one for Y, each with their own power and signal cables.

This device is long out of warranty, and official support ended in 2017. I don’t expect FormLabs to have a replacement galvo control board for this Form 1+, but it wouldn’t hurt to ask and see what they say.

FormLabs Form 1+ Printed a Shapeless Blob

I had been given a FormLabs Form 1+ resin printer that’s been sitting unused for years and requested to get it back up and running. Working with FormLabs equipment isn’t cheap, and this “free as-is” printer required nearly $300 of stuff just so I could see if it even runs. With the hardware in hand, I moved on to the software side of things.

All FormLabs equipment require their PreForm software to run, and the current version (3.25.2 as of writing) no longer supports the Form 1+. I dug through FormLabs support to find this page Using PreForm with the Form 1+ which provides a link to download PreForm 2.20. That was the final release before PreForm dropped support for this old printer. PreForm 2.20 is also available for download from the page listing PreForm versions and their equipment compatibility. If someone wants to go even older because they have a need for 32-bit edition, PreForm 2.16.0 was the final 32-bit release and available on that same page.

Installing and launching PreForm activated an introduction to the software, which guides us through printing the FormLabs test object: a (hair?) clip in the shape of FormLabs butterfly logo. I followed through the tutorial to properly orient the shape and generate supports. I installed the Form 1+ compatible aftermarket resin vat from Z-Vat industries, and poured in Form 1+ compatible aftermarket resin from ApplyLabWork. I hit print and started hearing the buzzing of the Z-axis stepper motor. A good sign! Given the upside-down printing nature of resin printers, the metal printing platform blocked my view of what it was doing. I left the machine alone to do its thing.

Roughly half an hour later, the print height has risen enough I could see between the print platform and the vat. I had hoped to see a sturdy print raft forming the foundation of my test clip, but I saw only a lumpy misshapen blob. This is not good.

Watching the machine work, I could see the laser illuminated only a single spot instead of sweeping through the shape as I had expected. I didn’t see movement from the resin vat, either, which was supposed to move as part of peeling process between layers.

After I cancelled the print job, the build platform was raised to its maximum height where I can confirm the misshapen blob. This is definitely not the intended test clip object. It isn’t even in the right place. The test clip was supposed to be close to the peeling hinge edge. (Right side edge in picture above.)

The unmoving laser beam is what hardened the blob. It also hardened various bits of resin which are now floating amongst still-liquid resin. I drained all of that contaminated resin into a disposal container that I will leave out in direct sunlight to harden. Wiping the resin vat clean of residue, I see a hole burned in the precious PDMS layer.

The good news is that all the aftermarket hardware I bought for this printer worked: the aftermarket AC power supply brick seemed to deliver enough power, the aftermarket resin hardened in response to the laser, and the aftermarket resin vat’s PDMS layer allowed the hardened resin to separate between layers. That’s great! But there is something wrong with the printer itself and I’ll take it apart to look for hints.

FormLabs Form 1+ Resin Printer in Unknown Condition

This FormLabs Form 1+ resin printer was purchased as part of a company’s R&D project. Presumably sometime between June 2014 when Form 1+ was released, and September 2015 when Form 2 launched. It printed a few things and sat neglected since. Recently it came into my possession in “AS-IS” condition delivered by someone several steps removed from that R&D project. The people in that project has since departed, and all he knew was that “something was wrong with it”. If I could produce satisfactory results from this printer, they may subcontract me to print some parts for them and earn an operator’s fee to run this machine that used to be theirs. If I fail, they’ll still be happy because it’s no longer uselessly taking up space gathering dust at their facility.

When this agreement was reached, the machine still had a resin vat that held resin left from its last print. Neither vat nor resin would be any use after several years of neglect. That plus the high probability of making a sticky resin mess meant they were disposed instead of shipped. I was not given the power adapter, either. During the years it sat unused, it had been moved from one workbench to another and became separated from its original AC power adapter.

Fortunately, FormLabs had the foresight to clearly specify power requirements right next to the power socket. I have several 24V DC adapters on hand, but none as high as 2.5A. The best on hand is a 1.5A unit, which I bought for the Neato vacuum charging experiment. I put the correct size barrel connector (5.5mm OD, 2.1mm ID) on the wire and plugged it in.

That was enough for the printer to go through its startup sequence. Now assured the printer at least powers up, I will order a 24V power supply that can supply more than 2.5A. (*) What else would I need to run this printer? The Form 1 and Form 1+ have fallen out of official FormLabs support since March 2017, so now the best reference material I have is the “Retro Form 1 Guide” compiled by a user and posted to FormLabs user forums.

Another consequence of being out-of-support is that FormLabs no longer sells replacement resin vats for the 1 and 1+. These are considered consumables due to something called “PDMS layer” at the bottom of the vat. PDMS in this context may or may not mean polydimethylsiloxane, but I understand it is something that gradually degrades during printing so it (and the resin vat it is attached to) needs to be replaced periodically. With FormLabs no longer supplying this consumable, I looked for aftermarket solutions and found Z-Vat Industries. They would sell me a replacement resin vat.

FormLabs also no longer sells their specifically formulated resin in bottles we manually pour into a Form 1 resin vat, only in cartridges for installation into Form 2 and 3 which dispenses resin automatically as needed. From this FormLabs forum thread, I learned that resins for DLP resin printers are very different formulation from resins designed for laser resin printers like this Form 1+. (Quick summary: laser resin is designed to be sensitive to a quick flash of intense laser beam, DLP resin is tuned for longer exposure to less-intense light.) This fact drastically limited my options of aftermarket resins, leaving a few vendors like ApplyLabWork. Looking over their catalog, I will avoid the brittle precision resins and order one of their resilient “Robust” resin.

Resin printing is expensive, and FormLabs resin printing more so! I’ve spent nearly $300.00 just so I can find out if the printer even works. And the answer was… it doesn’t.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Failed LewanSoul LX-16A Servos

I love the concept of serial bus servos, writing them up for the Hackaday audience and designing my Sawppy rover around the low-cost LewanSoul LX-16A serial bus servo. After a few years of actual use, it’s fair to say the honeymoon period is over. LX-16A availability were unreliable even before the global supply chain crunch, and now it’s even worse. Furthermore, the hardware has some really bad failure modes. Two people have experienced failure where battery voltage (~7.4V) get sent out to the USB 5V bus, killing whatever Raspberry Pi was connected via USB. I have firsthand experience where a failed LX-16A shorted battery power to ground, blowing the fuse and required field repair in the middle of Maker Faire. Due to these problems, I intend to move away from LX-16A for future projects.

Now I’m going to open up “FAILED SHORT” servo to look inside. Maybe there’s something visible relating to its failure.

On the upside, the mechanical bits look great. The gearbox used well-lubricated metal gears throughout, and there’s a decent looking ball bearing supporting the output shaft.

Nothing has obviously failed on this side of the control circuit board. The square chip appears to be the main processor. There are four lines of markings on this chip:

HL004
642GB
2634B071
ARM

A web search found this forum thread that identified the chip as a Nuvoton MINI54ZDE, a little Cortex-M0 processor at 24MHz. If I get into playing with ARM microcontroller programming, I might be tempted to connect to the row of five pins and see if I can get a debug connection to that chip. Obviously, if I were to do this, I would use a different LX-16A that doesn’t short power to ground.

The next two largest chips appear to be identical, both labeled with:

4606
GA7N3C

A search found these to be AO4606 MOSFET by Alpha & Omega Semiconductor.

I see no obvious signs of failure on the other side of the circuit board, either. I see an ALPS potentiometer for position sensing, and a 1117-3.3 LDO voltage regulator.

On the upside, the lack of visible failure meant the fuse did its job well, blowing before anything really bad happened to this board. The downside is I have no visual indication of what went wrong. I’m mildly tempted to power up this servo without a fuse just to see what component blows up.

I have another failed LX-16A, this one “merely” stopped moving. It was still communicating with the rest of Sawppy controller system, with all diagnostics information showing OK. Except it doesn’t move. Powering the DC motor directly got me some motion, so at least the mechanical side is fine.

Given the lack of motor movement, I thought perhaps one or both of the MOSFETs have fried. But they look fine on this unit. Nothing’s obviously gone wrong with the CPU, either.

Potentiometer looks fine, and the 1117 LDO appears intact.

These two teardowns failed to provide any illuminating insight. I saw nothing at all that would explain faulty behavior of these units. Looking on the bright side, I’m glad neither of these devices went up in smoke and their mechanicals are still sound. I could still control the mechanicals by replacing these failed control boards with a DC motor H-Bridge controller like the classic L298N or the newer DRV8833. Turning them into a pair of gearmotors with metal gears and a ball bearing on the output shaft.

Electronic Mosquito Trap

It’s summertime in Southern California, which means a surge of mosquito trying to harvest human blood. I do not appreciate being an excellent source of protein, and the weapon I find most satisfying for fighting back are electronic mosquito zapping paddles. Some call them electronic flyswatters but I think that’s a misnomer. At least around here, where our usual species of flies grow far too big to be caught in the mesh.

This one says “Electronic Mosquito Trap” right on the handle. There is an activity light visible through a clear plastic window, and barely readable on that clear plastic is “Little Angel”, possibly a brand. Powered by a pair of AA batteries, the voltage is drastically increased to build up a high potential difference between layers of metal meshes. When a mosquito tries to fly through those layers, they short the circuit ending their bloodsucking quest.

A household commodity made at great volume for low cost, they are practically disposable. This particular zapper was damaged when one of my vigorous swings crashed into the wall. The shattered rim of brittle plastic is cosmetic, but the mesh has also been bent so that the layers touch. It is no longer possible to build a high voltage potential between mesh layers, so it is time for a teardown before disposal.

I expected a voltage boost converter circuit within, implemented in the simplest and lowest cost method possible. I only recently learned to recognize a boost converter when I see one, and this guy certainly qualifies. Implemented with large through-hole components, it looks we have the basics of: a transistor, a coil, a capacitor, and a diode.

Boosted voltage are sent to metal layers via these wires, whose insulation was damaged during assembly at the factory. At least the plastic is still an insulator.

Indicator light wires were also damaged in assembly.

The yellow output wire was connected to the center layer of the mesh sandwich, the two red output wires (both soldered to the same point on the circuit board) are connected to the top and bottom meshes.

Learning more about boost converters is on my to-do list. After I have a better idea of what’s going on, I want to look at this circuit again. Perhaps I can make my own improvements on a mosquito zapper paddle!