FormLabs Form 1+ Stepper Motor Control

I have a broken FormLabs Form 1+ laser resin 3D printer and I’ve been figuring out how to operate subcomponents for potential repurposing in the future. I just got a basic (if imprecise and incomplete) understanding of how to operate its 64mW 405nm laser, which I considered the most challenging component. Now that’s done, I’ll wrap up my Form 1+ exploration by looking at what I considered the least challenging component: its two stepper motors.

The larger of these motors operate the Z-axis, the smaller one operates the resin tilt tray. Both of those have four-wire connector to the printer mainboard, with pins labeled A+/A-/B+/B-. This identifies them as bipolar stepper motors popular in the field of FDM 3D printers and thus quite familiar to me. In order to repurpose these motors elsewhere, I just need to know two parameters: their operating voltage and current limits.

To determine these values, I started by finding the existing stepper motor driver chip which was placed close to the two stepper motor connectors. It is a Texas Instruments DRV8821 dual stepper motor driver chip. The chip itself is capable of handling up to 32V and 1.5A but configured for lower values for use in this printer.

Voltage was easier to determine, as I looked up position of motor voltage (VM) pins on the chip and probe them while the printer is active. They measured 24V DC. Finding the current limit took a bit more work. DRV8821 datasheet section 7.3.2 Current Regulation gave the formula: (Current Limit) = (Reference Voltage) / (5 * Current Sensing Resistor). There are four current sensing resistors wired on the circuit board, so I had to figure out which motor is wired to which pins on the driver. Probing for continuity, I found the following:

MotorMainboard labelDRV8821 labelDRV8821 pin#
ZA+AOUT15
ZA-AOUT23
ZB+BOUT148
ZB-BOUT246
TiltA+COUT127
TiltA-COUT225
TiltB+DOUT122
TiltB-DOUT220

This tells me the current sensing resistors AISEN (DRV8821 pin 4) and BISEN (47) are associated with the Z-axis motor. Both are labeled R100 which I decoded to mean 0.1 Ohm. CISEN (26) and DISEN (21) are then for tilt motor which are labeled R200, for 0.2 Ohm. Probing the circuit while powered-up, I found the voltage dividing resistors supplying reference voltages and measured it at 0.5V for both ABVREF (17) and CDVREF (18).

Using DRV8821 datasheet formula, I calculate the following:

  • Z-axis stepper motor can be driven with 24V DC at a maximum of 0.5/(5*0.1) = 1A.
  • Tilt stepper motor can be driven with 24V DC at a maximum of 0.5/(5*0.2) = 0.5A.

FormLabs Form 1+ Laser Control Circuit (Partial)

So far, I’ve had only limited success deciphering operations of laser module in a FormLabs Form 1+ laser resin 3D printer. I knew it was a laser diode, but instead of just two wires for power+ground there are four wires snaking out the end of this module. My oscilloscope can show me how voltage varies during a print job and also during API programmatic control, but I didn’t know how to interpret those voltage values.

It’s time to move on to the next resource at my disposal. Beyond preserving the ability to run print jobs and programmatic access API, I also have the functioning printer mainboard itself I can examine. I’m only a beginner at electronics, but I can follow copper traces on a circuit board for a little bit before I get lost. As far as I can tell, the printer mainboard is a two-layer circuit board, meaning there aren’t hidden layers of copper that I could not trace. However, it makes copious use of vias to tunnel things from one layer to the other, and it’s hard for me to pick out the right via to follow when a copper path switches sides. And it doesn’t help that many traces run underneath components so I could not trace them.

My complaints aside, I was able to get far enough for some insights. The black wire is connected to the collector of a Fairchild Semiconductor (now onsemi) TIP122 power transistor, whose emitter is connected to the ground plane. Aha! Laser power is switched on the low side, explaining why I didn’t recognize voltage of red & black wires as power & ground wires.

So, what controls this TIP122 transistor? And what about the other two wires coming out of the laser module? Here I could uncover only part of the picture, but I know it centers around component U7, marked with Texas Instruments logo and labeled L358. The closest thing I found on TI website has an additional letter M: LM358 dual op-amp chip. It seems to fit, though. The V+ input pin is connected to 11.18V power like the laser module red wire, and the V- pin is connected to system ground. OUT1 connects to base of TIP122, so one op-amp on this chip is in charge of driving the laser power transistor. Laser module blue wire is connected to the other op-amp on this chip, pin IN2-. And this is where I got stuck. I couldn’t figure out the rest of this circuit, lost in the maze of traces.

My hypothesis is that L(M)358 is the heart an analog voltage control circuit utilizing closed-loop feedback provided by laser module blue wire to modulate laser power via TIP122 transistor. My comprehension isn’t enough to get further. Analog circuits using op-amps are still voodoo magic to me today. I hope I’ll learn enough in the future to return and decipher this circuit.

Though incomplete, this is enough understanding for me to know that I could ignore the blue and yellow wires if I don’t care about precise laser control. Putting power across red and black wires is enough to get a violet-blue laser dot. 3.7V will draw 20mA, values similar to non-laser LEDs. According to my OpenFL API experiment this would be slightly lower than 1mW of beam power. Which is generally regarded as relatively safe, low enough power that normal blink reflex is enough to prevent serious eye damage. 4.5V corresponds to the recommended maximum of 64mW, and 4.61V will push us all the way up to the not-recommended level of 80mW. I assume that ventures significantly into eye damage territory so if I must be careful with laser power levels if I should use it elsewhere.

Final step on my Form 1+ hardware tour: stepper motor controller.

FormLabs Form 1+ Laser Power During Print

I haven’t quite figured out how to control the laser module of a broken FormLabs Form 1+ resin laser 3D printer. I had thought getting programmatic control over the FormLabs OpenFL API would be key, but it wasn’t quite as illuminating as I had hoped. Though it’s still a step forward, giving me a table of wire voltages supplementing the on/off data points I obtained earlier. How can I obtain more data about operation of this laser? I have the electronics guts laid out on my workbench and voltage probes still in place so… I’ll run a print job!

Using the oscilloscope to watch voltages as the laser went about its business, it’s pretty clear that the red wire (channel 1 yellow line) is the power supply as it held constant. I see activity on the black wire (channel 4 green line) and blue wire (channel 3 blue line) that varies in intensity as the laser scanned across the shape. While they are at different voltage levels, they seem to flip between their individual set of two states in lockstep. It almost looks like a digital communication signal, but the voltage levels are too high for digital logic.

Zooming into these signals (100 milliseconds per grid down to 100 microseconds per grid) confirm that they are always moving in lockstep. Based on voltage levels, this represents the laser pulsing on and off rapidly, consistent with a laser tracing through multiple curves in a printed shape. The higher voltage levels here match the voltage levels I measured earlier for laser off. The lower voltage levels here are consistent with values in the range of tens of milliwatts of power.

Another thing I noticed in the zoomed-in view is the absence of PWM modulation artifacts. My own PWM circuits under an oscilloscope always show a noisy wave, expected for quick and dirty circuits built by electronics beginner like myself. Here we see the smooth analog voltage control of a circuit designed by people who knew what they were doing. I should take a closer look at the circuit board to see what I can learn.

FormLabs Form 1+ Laser Power via OpenFL

After FormLabs stoped supporting the Form 1/1+ printers, they released a set of tools collectively called OpenFL letting people play with the hardware. We can either stay within the realm of laser resin 3D printing or come up with something entirely different. After I successfully installed the toolset and established Python communication with the printer, I wanted to explore the laser module.

At the top of Printer.py I see two references to laser power: an audit toggle and a power ceiling of 64mW.

    AUDIT_LASER_POWER = True
    LASER_POWER_MAX_MW = 64

Looking for where the ceiling is used, I found this method:

    def check_laser_ticks(self, power):
        """ Raises if the power (in laser ticks) is above our safe threshold
        """
        mW = self.ticks_to_mW(power)
        if mW > self.LASER_POWER_MAX_MW:
            raise LaserPowerError('Requested power is dangerously high.')

From this method I learned laser power is measured in two different ways: “ticks”, which is a hardware-specific measure, and the more general units of “mW” (milliwatts). There are two methods to convert between them. The ticks_to_mW seen here, and its inverse mW_to_ticks. Reading those methods, I see that ticks is an uint16 (unsigned 16-bit integer) value so valid range is 0 to 65535. So what’s the maximum possible power via this API?

>>> p.ticks_to_mW(65535)
80.71

So 64mW is the recommended maximum, any higher may raise LaserPowerError but if we have the option to ignore that and turn the dial up to 80.71mW.

I also see that the conversion depends on a laser power lookup table presumably established with factory calibration and saved in nonvolatile memory. Using OpenFL we can see that table.

>>> p.read_laser_table()
[[0, 0, 0], [0.1, 0.02, 9.0], [0.2, 0.03, 12.0], [0.3, 0.03, 14.0], [0.4, 0.04, 16.0], [0.5, 0.05, 18.0], [0.6, 0.06, 19.0], [0.7, 0.07, 22.0], [0.8, 0.1, 24.0], [0.9, 0.23, 25.0], [1.0, 3.77, 26.0], [1.1, 8.22, 28.0], [1.2, 12.76, 29.0], [1.3, 17.34, 30.0], [1.4, 22.06, 32.0], [1.5, 26.73, 33.0], [1.6, 31.53, 34.0], [1.7, 36.33, 35.0], [1.8, 41.11, 36.0], [1.9, 46.0, 37.0], [2.0, 50.92, 38.0], [2.1, 55.92, 39.0], [2.2, 60.72, 40.0], [2.3, 65.81, 41.0], [2.4, 70.8, 41.0], [2.5, 75.79, 42.0], [2.6, 80.71, 43.0]]

Actually powering up the laser requires calling one of several methods, which accept input in some combination of machine coordinates or real dimensions. I chose to experiment using set_laser_mm_mW() which simultaneously updates galvanometer position and laser power. For my first test I set the laser to 1 milliwatt.

>>> p.set_laser_mm_mW(0, 0, 1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "c:\users\me\openfl\OpenFL\Printer.py", line 502, in set_laser_mm_mW
    return self.set_laser_uint16(x, y, self.mW_to_ticks(mW))
  File "c:\users\me\openfl\OpenFL\Printer.py", line 485, in set_laser_uint16
    expect_success=True)
  File "c:\users\me\openfl\OpenFL\Printer.py", line 180, in _command
    r = self._wait_for_packet(wait, verbose=verbose)
  File "c:\users\me\openfl\OpenFL\Printer.py", line 195, in _wait_for_packet
    p = self.poll()
  File "c:\users\me\openfl\OpenFL\Printer.py", line 220, in poll
    self._process_raw(raw)
  File "c:\users\me\openfl\OpenFL\Printer.py", line 150, in _process_raw
    cmd = Command(self.packet[1])
  File "C:\Users\me\miniconda3\envs\openfl\lib\site-packages\enum\__init__.py", line 348, in __call__
    return cls.__new__(cls, value)
  File "C:\Users\me\miniconda3\envs\openfl\lib\site-packages\enum\__init__.py", line 663, in __new__
    raise ValueError("%s is not a valid %s" % (value, cls.__name__))
ValueError: 147 is not a valid Command

Hmm. There’s a problem with OpenFL Printer API class processing response packet from the printer. But the outgoing command apparently works, because I got a dim glow from the laser. Following that with p.set_laser_mm_mW(0, 0, 0) turned the laser back off along with another ValueError: 147. This is good enough for me to set up some voltage probes. The laser has four wires: red, black, blue, and yellow. Here are their voltages at various milliwatt settings, relative to yellow which is connected to ground.

Power (mW)RedBlackBlue
0 (OFF)11.208.674.89
111.207.403.75
1011.207.273.61
2011.197.123.52
3011.197.013.44
4011.186.913.36
5011.186.803.28
6011.186.713.24
7011.176.633.20
8011.166.553.14

These values weren’t as enlightening as I had hoped they would be, but maybe these snapshots will make more sense in the context of a normal print job.

FormLabs Form 1+ OpenFL API Connection

I had a longshot idea to revive the galvanometer control of a broken FormLabs Form 1+ resin laser 3D printer. It didn’t work and galvanometer remains broken. Because the printer also had a broken resin tray tilt motor and other smaller problems, I wasn’t trying to get it to print again. What I had in mind was to repurpose the optical core into a laser light show machine.

This was made possible because FormLabs opened up the Form 1/1+ for experimentation after they stopped supporting the hardware. Since they are no longer responsible if anything goes wrong, they freed the hardware for people to mess around with. This consisted of a special build of the PreForm software, which will flash a special (final?) edition of firmware. This firmware is willing to talk to a PC beyond accepting print jobs from PreForm. To make this communication easier, they released a Python library. All of these were posted on a GitHub repository under their “OpenFL” umbrella.

I really appreciate the fact FormLabs did this, exposing an API to control hardware independently of PreForm print jobs make it possible to do things completely outside the realm of printing. One of their examples turn the Z-axis stepper motor into a single-channel MIDI instrument making buzzy electromechanical music. The API also allows control of laser power and galvanometer position, which lead to my idea of turning the printer into a laser light show machine.

But first, I had to get it up and running. The first problem is that, as a seven-year-old Python library, it was written for Python 2 which is now discontinued. To create a backwards compatible Python environment, I used Miniconda to create a Python 2 environment called “openfl”

conda create --name openfl python=2

Following instructions in OpenFL repository I setup and installed Python dependencies. It allowed me to load OpenFL library but I immediately ran into an error.

Python 2.7.18 |Anaconda, Inc.| (default, Apr 23 2020, 17:26:54) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from OpenFL import Printer as P
>>> p = P.Printer()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "OpenFL\Printer.py", line 62, in __init__
    self.dev = usb.core.find(idVendor=self.VID, idProduct=self.PID)
  File "C:\Users\me\miniconda3\envs\openfl\lib\site-packages\usb\core.py", line 1297, in find
    raise NoBackendError('No backend available')
usb.core.NoBackendError: No backend available
>>>

This “No backend available” error came from pyusb library, complaining about a missing dependency outside of Python: we need a compatible USB driver installed. Solving this error required the following chain of events:

  1. Read up on PyUSB at https://pyusb.github.io/pyusb/
  2. Which point me to LibUSB at https://libusb.info/
  3. Which pointed me to its Wiki for running on Windows at https://github.com/libusb/libusb/wiki/Windows#How_to_use_libusb_on_Windows
  4. Which recommended the Zadig utility at https://zadig.akeo.ie/

Zadig offered several options for USB drivers, I tried them in the order recommended by LibUSB.

  1. WinUSB (v6.1.7600.16385): nope, still got “No backend available” error
  2. libusb-win32 (v1.2.6.0): looks good!
Python 2.7.18 |Anaconda, Inc.| (default, Apr 23 2020, 17:26:54) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from OpenFL import Printer as P
>>> p = P.Printer()
>>> p.state()
<State.MACHINE_READY_TO_PRINT: 3>
>>>

I’m in! Now to poke around and see what I can do with the laser.

FormLabs Form 1+ Electrical Failure Reproduced

I’ve taken apart a broken FormLabs Form 1+ laser resin 3D printer and laid out its entire electrical system on my workbench. Freed of most of its mechanical parts, it is a much more compact and easily explored layout. Ideal for me to try my long shot idea, which came to me when I started closely examining the damaged galvanometer control board and guessing at how it worked.

The hypothesis: root cause of failure may be a badly crimped connector, which is a common failure mode. It worked well enough to pass FormLabs quality assurance, but presented higher resistance than was desirable, wasting power as heat. Functionally it was probably fine, as this wire carried -24V which was converted to -15V DC by a voltage regulator. So if the extra resistance dropped a volt or two it would not have been noticed. But as time went on, this heat would have weakened and damaged things, raising resistance and temperature. Until one day things got hot enough to reach ignition temperature and started our electrical fire.

The examination: With the system powered up, I probed the front and confirmed -24V on the purple wire. Flipping the board over (an easy task now everything is laid out on workbench) I could access pins corresponding to the connector. I confirmed +24V and ground were as expected, and also confirmed only 0.6V DC instead of -24V DC on the final pin. To double-check, I also probed the input pin of L79 negative voltage regulator, and it also showed 0.6V DC. The -24V DC plane is not receiving -24V, consistent with the burned-out connector hypothesis.

The experiment: I cut the purple wire and soldered it directly to the connector pin on the back. If the connector was the only problem, this would bypass that connection and revive the galvanometer control board. If the connector is not the only problem, I have replicated the conditions leading to that electrical fire. I turned everything on and witnessed the following sequence:

  1. An orange glow at the base of the visibly burnt area. (Not in the connector.)
  2. Foul-smelling smoke from the new recreated fire.
  3. Heat melted solder and released the newly connected wire, breaking the connection and preventing any further damage.

The conclusion: I successfully replicated the conditions leading up to an electrical fire. Whatever went wrong on this board, it isn’t a bad connector. Or at least, not just a bad connector. This was an easy thing to try and I wanted to give it a shot. It would have been a great story if this had worked! I even had some ideas on what I would do with it.

FormLabs Form 1+ Internals on Workbench

I’ve been taking apart a broken FormLabs Form 1+ laser resin 3D printer because I wanted to learn as much as I can from a piece of hardware I probably wouldn’t have bought on my own. Also, it is taking up too much space. Once I separated the Z-axis subassembly from the rest of the printer chassis, I could place the entire electrical and electronics nervous system on my workbench. The printer wouldn’t print anything in this state, of course, but it thinks it could. I’m very amused to read “Ready to print” on the OLED status display.

My first experiment with this “benchtop printer” is to see what components are necessary to run through a print program. I knew some connections between components must have been open-loop, because the printer mainboard had no idea the galvanometer control board was fried nor that the resin tray tilt motor was damaged. What else is the mainboard unaware of? Here are my findings:

OK to disconnect:

  • GALVO X SIGNAL, GALVO X POWER, GALVO Y SIGNAL, and GALVO Y POWER. The galvanometers are a motor+sensor combination and requires closed-loop control with the galvanometer control board. However, the connection from printer mainboard to galvo control board is open loop.
  • TILT stepper motor is open-loop control, mainboard has no feedback on resin tray position.
  • LASER could be disconnected and still allow print program to run.
  • DISPLAY is one-way SPI communication.
  • LED wires for BUTTON is optional.

Needs to be connected:

  • INTERLOCK door safety is something the mainboard definitely checks. It can be bypassed by taping a magnet onto the sensor. Could also try connecting the sensor wire (blue) to ground (black) but I have not tried this.
  • Switch wires for BUTTON is needed for a confirmation press before printing process begins.
  • Z LIMIT and Z MOTOR are required to run through Z-axis homing procedure.

Laying out all the components on a workbench in running condition also lets me try a long shot idea: providing alternate negative voltage path for galvanometer control.

FormLabs Form 1+ Z-Axis Assembly

I think I can find new useful homes for several components of a broken FormLabs Form 1+ laser resin 3D printer. After carefully removing its laser optical core, I proceed to attempt salvaging its Z-axis actuator.

The Z-axis motion in this printer is driven by a stepper motor turning an Acme thread leadscrew. This concept is pretty commonly found in FDM 3D printers as well, but closer inspection unveiled a higher quality design. The first hint was the limit switch at the top. Cheap FDM printers use a microswitch, this printer uses an optical interrupter. Eliminating the flexible spring in a microswitch makes this limit switch more precise in marking its location. The print platform is mounted on a ball bearing carriage traveling on a guide rail, again more precise than the typical FDM printer usage of sleeves traveling on rods.

And finally, I noticed a detail significant in its absence: there is no shaft coupler between motor and leadscrew. A leadscrew as motor output shaft eliminates all problems introduced by couplers. No set screws to back out, no errors in concentricity between the two shafts, etc. Markings on the motor says LDO-42STH34-L291E. We can find LDO Motor’s page for their LDO-42STH line of 42mm hybrid stepper motors, but this particular model number is not listed. Searching for similar items revealed several other LDO motors with a leadscrew output shaft, all at significantly higher cost than generic NEMA17 stepper motors + leadscrew + coupler. Looks like this particular FormLabs motor variant is an engineering tradeoff of higher parts cost for higher precision.

However, all this precision means I have to make a decision on salvaging these parts. The linear rail, optical interrupter limit switch, and stepper motor are all mounted to the printer chassis. The chassis is constructed from several sheets of stamped sheet metal, folded and riveted together for rigidity. Good for optical stability, bad for me. If I remove each component separately, their relative precision alignment would be lost. If I want to remove the Z-axis as an intact sub assembly from the printer chassis, I have to perform the irreversible act of drilling out some rivets. After some thought I decided on the latter option.

Drilling out rivet heads would generate a lot of metal shavings. So before I got started with that destructive act, I wanted to remove the main mirror and get it away from scratch-inducing shavings.

The back side of the mirror has been glued to a metal plate with two embedded threaded rods. Removing two nuts freed the mirror assembly.

With the mirror stored safely away, it’s time to make some chips.

Roughly half an hour later, I’ve freed the Z-axis subassembly from all other pieces of stamped and riveted sheet metal.

I thought about grabbing my angle grinder to cut off the bottom, as it is not strictly related to the Z-axis assembly. But this is where the laser optical subassembly was mounted, and it’s also where the mirror was mounted. There’s a chance these pieces of sheet metal may yet be useful. Besides, it’s only minimally more than keeping the Z-axis itself. Even with this bottom portion, this subassembly is a lot less bulky than keeping the rest of the printer chassis together. And small enough for me to lay out everything on my workbench.

FormLabs Form 1+ Optical Core

Too many things have gone wrong with this old FormLabs Form 1+ laser resin 3D printer for me to think I could return to precision printing duty. A broken resin tray tilt motor was just the latest discovery added to that pile. But it’s such an interesting machine to take apart, filled with precision components that I don’t know how to use but couldn’t bear to pitch in the garbage. Top among this list is this laser optical core.

A precision machined piece of aluminum is home to four important optical components: The laser itself in a black cylinder, emitting a beam to strike two mirrors. Each mirror adhered to the end of two orthogonally mounted galvanometers. After bouncing off these two rotating mirrors, the beam strikes a small front-surface mirror directing the beam into the large center cavity. In that cavity is a much larger main mirror, who is angled to deflect the beam up into the resin tray to precisely harden some resin for the print.

Before I removed the core, I ran the optical path one last time. In place of the resin tray, I have placed a sheet of normal white office printer paper. I had no concept of the power level of this laser and wanted to see what it would do. The answer: no hole, no fire, no smoke, not even a little brown singe mark. Just a bright dot. I suppose it is possible that this laser isn’t driven at maximum power, but I am comforted to know that my initial fear of rampant laser destruction was misplaced. However, I will continue to assume it is powerful enough to cause eye damage and deserving of respect.

When removing this optical core, take care not to just blindly loosen every visible fastener. The three most visible fasteners are actually holding the laser and galvanometers in place. The galvanometer fasteners can be loosened in order to rotate the galvanometer to center their range of rotation and thus center the beam. I don’t know if similarly rotating the laser module would accomplish anything.

To remove the optical core, we actually need to unscrew the two deep set fasteners in opposing corners. These fasteners provide the force to hold the optical core in place, their orthogonally opposite corners host two alignment pins to locate the optical core on the printer chassis main spine.

At the moment I don’t know the electrical requirements to driver any of these three components, but I will try to keep this fragile optical core intact in case I can return with more knowledge about how to make them run. I also want to keep the Z-axis assembly, which is thankfully more robust than delicate optical components.

FormLabs Form 1+ Resin Tank Tilt Mechanism Damaged

I’ve been exploring several subsystems of a broken FormLabs Form 1+ laser resin 3D printer. After a rather disappointing session playing with its serial interface console, I’ve exhausted the list of electronics to explore and moving on to mechanical systems. First on the list: the resin tank tilting mechanism. I believe this is done to help with the peeling the partial print away from PDMS layer, but maybe more importantly, redistribute resin across the tank between layers. Tilt has stopped working on this printer, and I wanted to look for anything that might explain why.

Looking at the top part I see a leadscrew mechanism, but it wasn’t immediately obvious how it worked. Everything I see here seems to be rigidly fastened to something. I couldn’t rotate anything by hand. What was supposed to rotate on this mechanism driven by a stepper motor?

Once I could see the lower half of this mechanism, I saw why it failed: this white plastic portion has separated from the rest of the motor, no longer held by stamped sheet metal claws all around its perimeter.

Visible from the bottom is another problem: on either side of this motor are small hooks on the resin tray carrier. Each of which has a corresponding slot in the chassis. But there’s an alignment problem: the hook on the left side of this picture (front of the printer) looks good, but the right side (rear of the printer) hook is no longer aligned with its slot. This misalignment makes it very difficult to raise the resin tray back into place, and that stress might have contributed to white motor bottom pop out.

I saw no obvious explanation for the misalignment. There were no signs of distortion on the printer chassis, nor do I see any obvious problems with the tilt hinge. It was a surprise to see the hinge itself, though. With all the precision parts I’ve seen inside this laser instrument, it was jarring to see something resembling a cheap piano hinge I could get at the local hardware store.

Once I removed the motor, I could read its sticker:

LDO-35BYZ-B01-12    PM STEPPER
LDO MOTORS            20150320

20150320 is probably a date of manufacture, March 2015 is within range of Form 1+ production.

LDO-35BYZ-B01-12 led me to information page for LDO Motors company’s line of 35mm linear PM stepper motors. Where I learned the only rotating part is inside the motor enclosure, acting upon the leadscrew passing through motor centerline. This is very novel to me, as it means there’s nothing to rotate externally and risk tangling wires. This motor is designed so there is only a linear motion in the output shaft. Either the motor can remain still and impart a linear motion to the shaft, or the motor could move along a static shaft. A Form 1+ bolted motor to chassis and its threaded output shaft is attached to the end of the resin tray carrier. Unfortunately, something went wrong with the tray tilt mechanism, exceeding the designed forces of this motor and breaking it.

I pushed on the dislocated white portion and, to my mild surprise, it was willing to pop back into place. The motor resumed operating as a linear actuator. Of course, this part has now been weakened so it is no longer as capable as it was when new. If I should try to reuse this linear actuator in another project, I’ll have to use it where the physical pushes in the opposite direction and/or supplement its failed metal claws with an external brace.

Next step on my hardware tour: the optical core.

FormLabs Form 1+ Serial Console Disappointingly Uninformative

I had a lot of fun with the OLED dot matrix display from a broken FormLabs Form 1+ laser resin 3D printer. It exhibits a slight bit of burn-in from its career as printer status display, but after my exploration I’m confident I can put it to use. Now I wrap up my exploration of Form 1+ mainboard with the 6-pin header in the corner labeled CONSOLE.

Out of 6 pins, three were labeled G, T, and R. G was a good candidate for ground, and my meter confirmed it had continuity to the ground plane. T and R would be good candidates for “Transmit” and “Receive” wires of a serial port. I first connected it to my oscilloscope to confirm these are 3.3V signals, then I connected it to my FTDI USB to serial bridge to see what’s shown on that console. I received legible data when configured serial port as follows:

  • 115200 baud
  • 8 data bits
  • 1 stop bit
  • No party
  • No flow control

I had hoped I would see low level information on this serial link, starting with perhaps the firmware version number. Since it is labeled CONSOLE I had also hoped for an interactive command prompt to query status and maybe diagnostics commands. Sadly, that did not seem to be the case. Or if it is, it required magic keypresses that I don’t know. There was no response to anything I tried. (Escape, Control+C, the usual suspects.)

Here’s what I saw upon power-up, with the unique items highlighted.

Starting setup...
initializing USB
setting up user interface
setting up ui spi port
starting UI timer
powering up SD card
setting up laser...
initializing temperature sensor...
setting up motors
setting up SD card
setting up print block processor
setting up odometer
...setup complete.

After powerup I pressed front panel button for printer startup. I saw a very similar but slightly different set of text. The differences are highlighted:

Starting initialize.
setting up user interface
setting up ui spi port
starting UI timer
powering up SD card
setting up laser...
initializing temperature sensor...
setting up motors
setting up SD card
setting up print block processor
setting up odometer
...setup complete.
turning on power.
initialization done

Beyond that… nothing. Nothing while downloading a print job, nothing while it is printing. I had hoped this serial console would display a superset of status information shown on front panel OLED display, but this is more likely a development feature that’s severely limited when running customer facing firmware. Oh well, at least I looked. And now it’s time to take apart some mechanical bits.

FormLabs Form 1+ OLED Burn-In

I’ve been playing with the OLED dot matrix display from a broken FormLabs Form 1+ laser resin 3D printer. After I explored all the functional aspects and documented its pinout information, I thought I’d explore a side curiosity: is there any visible burn-in on this OLED panel?

A characteristic of OLED technology is that the longer an OLED element has been shining, the dimmer it becomes. Usage pattern is a huge part of whether OLED dimming becomes a problem. If an OLED screen constantly shows static information, certain pixels would be illuminated for disproportionate amount of time relative to their neighbors. In this scenario, constantly illuminated pixels age much faster than their neighbors, and their difference in brightness results in “burning in” the static image. For example, OLED panels used for watching television or movies have working fine for years. But those same panels would show burn-in after a few months if used as static display for information. Displaying 3D printer status is definitely towards the unfriendly side of the spectrum, which is why I was surprised when I learned FormLabs used an OLED here. Did they make a bad decision? Could I detect signs of burn-in on this Form 1+ display?

While running the Adafruit example sketch, I didn’t notice anything obvious. This would support the optimistic view that any burn-in is negligible. But since I had the SSD1305 API at hand, I added a bit of code for full-screen white which illuminated all pixels at max power. When I did this, I could see signs of burn-in, but it is subtle. It is certainly very difficult to capture in a photograph, as I’m also fighting OLED refresh rate at the same time as I’m trying to capture a low-contrast effect. The title image for this blog post shows an unmodified picture where the burn-in effect is barely visible.

This image has been modified to enhance contrast, making the burn-in a tiny bit more visible. For reference, the information shown by a Form 1+ while printing is in the format of:

Job: "[Filename]"
HH:MM:SS remaining
Layer X of Y

Unchanging text “Job”, “remaining” and “Layer” are visibly burned in. Remaining variable data end up in a more distributed blur. Pixels between lines of text are rarely illuminated, so those lightly used pixels show up brighter than the rest. Still don’t see it? Perhaps it would help to have a set of text overlaid in red:

The unknown variable is how long this printer operated before it retired. If this printer provided many years of service and this is all we see after years of constant display, then I would grudgingly admit burn-in is negligible. If this printer only printed a few jobs before dying, then this is horrible. With these pictures I can conclude OLED burn-in is real, but this incomplete data point is not enough to say whether OLED burn-in is a real problem of concern.

One thing I did notice, though: FormLabs chose an LCD module for their Form 2 printers’ front panel display. That might be the most telling sign. I have yet to see a Form 3 in person, but I would expect an LCD for that as well. Maybe an OLED status panel isn’t the greatest idea if it would eventually render the machine unusable. Perhaps there are other ways to obtain printer status information? Earlier I noticed what might be a serial port on the mainboard, so I’m going to look into that.

FormLabs Form 1+ OLED Pinout

I have a broken FormLabs Form 1+ laser resin 3D printer and I’m learning what I can from taking it apart. On its front panel is a small OLED dot-matrix display that I have been exploring. I have now successfully controlled that OLED module using an ESP8266 development board.

Confirming the speculation in this FormLabs forum thread, the OLED module is very similar to the Newhaven Display International NHD-2.23-12832UCB3. Both of their display areas are 2.23″ diagonal with 128×32 pixels of resolution. They both use a SSD1305 controller, but while Newhaven’s module provided a single row of 20 pins, FormLabs custom built their own circuit board connecting to the rest of the printer with a 10-wire IDC ribbon cable. Only 7 wires are actually used.

This OLED module is also very similar to Adafruit product #2675 Monochrome 2.3″ 128×32 OLED Graphic Display Module Kit but without Adafruit luxuries like 5V logic level shifter and power buffering capacitor.

This module only requires a power supply of 3.3V DC, because it has an onboard voltage boost converter to supply other voltages needed by OLED. All logic high signals are also 3.3V DC. Data communication is via SPI protocol with an additional command/data select input wire. When that wire low, the chip will interpret SPI traffic as commands and when high, SPI traffic will be sent to graphics frame buffer.

  1. Ground
  2. Vcc to supply 3.3V DC
  3. Command/Data select
  4. SPI Clock
  5. Reset (Active Low)
  6. SPI Data In (*)
  7. SPI Chip Select (Active Low)
  8. Unused
  9. Unused, but connected to mainboard I2C bus data line
  10. Unused, but connected to mainboard I2C bus clock line

(*) There is no SPI Data Out pin.


Now this pinout is documented, I will explore side curiosities like potential OLED burn-in.

Adafruit SSD1305 Arduino Library on ESP8266

Thanks to Adafruit publishing an Arduino library for interfacing with SSD1305 display driver chip, I proved that it’s possible to control an OLED dot matrix display from a broken FormLabs Form 1+ laser resin 3D printer. But the process wasn’t seamless, I ran into several problems using this library:

  1. Failed to run on ESP32 Arduino Core due to watchdog timer reset.
  2. 4 pixel horizontal offset when set to 128×32 resolution.
  3. Sketch runs only once on Arduino Nano 33 BLE Sense, immediately after uploading.

Since Adafruit published the source code for this library, I thought I’d take a look to see if anything might explain any of these problems. For the first problem of watchdog reset on ESP32, I found a comment block where the author notes potential problems with watchdog timers. It sounds like an ESP8266 is a platform known to work, so I should try that.

  // ESP8266 needs a periodic yield() call to avoid watchdog reset.
  // With the limited size of SSD1305 displays, and the fast bitrate
  // being used (1 MHz or more), I think one yield() immediately before
  // a screen write and one immediately after should cover it.  But if
  // not, if this becomes a problem, yields() might be added in the
  // 32-byte transfer condition below.

While I’m setting up an ESP8266, I could also try to address the horizontal offset. It seems a column offset of four pixels were deliberately added for 32-pixel tall displays, something not done for 64-pixel tall displays.

  if (HEIGHT == 32) {
    page_offset = 4;
    column_offset = 4;
    if (!oled_commandList(init_128x32, sizeof(init_128x32))) {
      return false;
    }
  } else {
    // 128x64 high
    page_offset = 0;
    if (!oled_commandList(init_128x64, sizeof(init_128x64))) {
      return false;
    }
  }

There was no comment to explain why this line of code was here. My best guess is the relevant Adafruit product has internally wired its columns with four pixels of offset, so this code makes a shift to compensate. If I remove this line of code and rebuild, my OLED displays correctly.

As for the final problem of running just once (immediately after upload) on an Arduino Nano 33 BLE Sense, I don’t have any hypothesis. My ESP8266 happily restarted this test sketch whenever I pressed the reset button or power cycled the system. I’m going to chalk it up to a hardware-specific issue with the Arduino Nano 33 BLE Sense board. At the moment I have no knowledge (and probably no equipment and definitely no motivation) for more in-depth debugging of its nRF52840 chip or Arm Mbed OS.

Now I have this OLED working well with an ESP8266, a hardware platform I have on hand, I can confidently describe this display module’s pinout.

First Test with Adafruit SSD1305 Library

I feel I now have a good grasp on how I would repurpose the OLED dot matrix display from a broken FormLabs Form 1+ laser resin 3D printer. I felt I could have figured out enough to play back commands captured by my logic analyzer, interspersed with my own data, similar to how I controlled a salvaged I2C LCD. But this exploration was much easier because a user on FormLabs forums recognized the SSD1305-based display module. Thanks to that information, I had a datasheet to decipher the commands, and I could go searching to see if anyone has written code to interface with a SSD1305. Adafruit, because they are awesome, published an Arduino library to do exactly that.

Adafruit’s library was written to support several of their products that used an SSD1305, including product #2675 Monochrome 2.3″ 128×32 OLED Graphic Display Module Kit which looks very similar to the display in a Form 1+ except not on a FormLabs custom circuit board. Adafruit’s board has 20 pins in a single row, much like the Newhaven Display board but visibly more compact. Adafruit added level shifters for 5V microcontroller compatibility as well as an extra 220uF capacitor to help buffer power consumption.

Since the FormLabs custom board lacked such luxuries, I need to use a 3.3V Arduino-compatible microcontroller. The most convenient module at hand (because it was used in my most recent project) happened to be an ESP32. The ssd1305test example sketch of Adafruit’s library compiled and uploaded successfully but threw the ESP32 into a reset loop. I changed the Arduino IDE Serial Monitor baud rate to 115200 and saw this error message repeating endlessly every few seconds.

ets Jun  8 2016 00:22:57

rst:0x8 (TG1WDT_SYS_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0030,len:1344
load:0x40078000,len:13516
load:0x40080400,len:3604
entry 0x400805f0
SSD1305 OLED test

Three letters jumped out at me: WDT, the watchdog timer. Something in this example sketch is taking too long to do its thing, causing the system to believe it has locked up and needs a reset to recover. One unusual aspect of ssd1305test code is that all work live in setup() leaving an empty loop(). As an experiment, I moved majority of code to loop(), but that didn’t fix the problem. Something else is wrong but it’ll take more debugging.

To see if it’s the code or if it is the hardware, I pulled out a different 3.3V microcontroller: an Arduino Nano 33 BLE Sense. I chose this hardware because its default SPI communication pins are those already used in the sample sketch, making me optimistic it is a more suitable piece of hardware. The sketch ran without triggering its watchdog dimer, so there’s an ESP32 incompatibility somewhere in the Adafruit library. Once I saw the sketch was running, I connected the OLED and immediately saw the next problem: screen resolution. I see graphics, but only the lower half. To adjust, I changed the height dimension passed into the constructor from 64 to 32. (Second parameter.)

Adafruit_SSD1305 display(128, 32, &SPI, OLED_DC, OLED_RESET, OLED_CS, 7000000UL);

Most of the code gracefully adjusted to render at 32 pixel height, but there’s a visual glitch where pixels are horizontally offset: the entire image has shifted to the right by 4 pixels, and what’s supposed to be the rightmost 4 pixels are shown on the left edge instead.

The third problem I encountered is this sketch only runs once, immediately after successful uploading to the Nano 33 BLE Sense. If I press the reset button or perform a power cycle, the screen never shows anything again.

Graphics onscreen prove this OLED responds to an SSD1305 library, but this behavior warrants a closer look into library code.

FormLabs Form 1+ OLED Screen Updates

It looks like the OLED dot matrix display in my broken FormLabs Form 1+ laser resin 3D printer uses a SSD1305 controller, based on communication traffic captured during its initial power-up sequence. Walking through that data while cross-referencing with the SSD1305 datasheet taught me a lot, and now I can apply this knowledge to examine logic analyzer traces from OLED reacting to other printer activities.

The Form 1+ doesn’t really have a power switch. When the 24VDC power supply is plugged in, it immediately starts running which includes the OLED power-up sequence I examined. But the user doesn’t see anything, because OLED display frame buffer has been filled with all black pixels. It’s not until they press the front panel button does the OLED start displaying visible pixels, and I have a logic analyzer trace of this startup sequence.

Visually, the startup sequence is a short animation of FormLabs text and butterfly logo. From off the bottom of the screen, it translates upwards until the text and logo is centered on screen for a brief second marking the end. From that point on, the screen is used to display up to four lines of text. Before this animation started, I see an initialization sequence identical to the power-up sequence: set all parameters and clear all eight memory pages to zero. After that, the animation starts running. When reading the SSD1305 datasheet, I saw it had a vertical scroll mode where bitmap in memory can be scrolled by changing the rendering start address. I thought that’s what the FormLabs animation used, but it wasn’t. Each frame of the animation is a full screen update sending four blocks of data for pages 0-3.

It appears memory pages 4-7 are not actively used for this application, which makes sense as the SSD1305 is designed for up to 132×64 pixels and we only have 128×32 on this OLED. However, those four pages of update data are transmitted in reverse order. Page 3 first, then 2, then 1, then 0. I wonder why? Hypothesis: This is to minimize visual artifacts. Imagine what happens if we update a memory page at the exact same time SSD1305 is displaying data from that page. We’d see a part of the old image mixed in with the updated image. Assuming the SSD1305 renders in increasing page order, sending data in the same increasing order means worst case unlucky timing will mess up all four pages. But if we update page in decreasing order, even the unluckiest timing scenario means only one out of four pages would be messed up.

Guesses or not, I feel like I have a pretty grasp of this OLED display module. Enough to try controlling it with my own code.

FormLabs Form 1+ OLED Control Consistent with SSD1305

I’ve been looking at various components of a broken FormLabs Form 1+ laser resin 3D printer, right now the focus is its front panel dot matrix OLED display. My first attempt at using a logic analyzer on its control signals told me which wires were active, but the actual data were gibberish. Fortunately, a second attempt retrieved sensical data waveforms. Someone on the FormLabs forums speculated this was an OLED display built around a SSD1305 controller, so now I will see if my captured data matches commands listed in SSD1305 documentation.

This stream of data represents system powerup, a set of commands (channel 0 white line is low) sent just before the first batch of data (channel 1 white line is high). If I interpret these bytes in context of SSD1305 datasheet, I get the following:

  • 0xAE: Display OFF.
  • 0xD5 0x10: Set display clock divide ratio to 1:1 and oscillator frequency to 300kHz.
  • 0xA8 0x1F: Set multiplex ratio to 31. (0x1F)
  • 0xD3 0x00: Set display offset to zero.
  • 0x40: Set display start line to zero.
  • 0xAD: Master Configuration for external Vcc power supply.
  • 0x8E: ???
  • 0x20 0x02: Set memory addressing mode to 0x02 (Page Addressing Mode.)
  • 0xA0: Set segment remap to 0 (Column address 0 is SEG0)
  • 0xC8: Set COM output scan direction to 1 (Remapped mode. Scan from COM[N~1] to COM0)
  • 0xDA 0x12: Set COM pins hardware configuration. (Disable COM Left/Right remap, Alternative COM pin configuration.)
  • 0x91 0x3F 0x3F 0x3F 0x3F: Set current drive pulse width of BANK0, color A, B, and C all to maximum valid value of 0x3F (63 clocks).
  • 0x81 0xFF: Set contrast control for BANK0 to 0xFF. (256, which is maximum contrast.)
  • 0x82 0xFF: Set brightness for area color banks to 0xFF. (256, which is maximum brightness.)
  • 0xD9 0xD2: Set precharge period to 0xD2. (Phase 1 period of 0x2 clocks, phase 2 period of 0xD or 13)
  • 0xDB 0x08: Set VCOMH Deselect Level to 0x08, but 0x08 is not in the list of valid values?
  • 0xA4: Entire display ON to display RAM content.
  • 0xA6: Set Normal Display. (Instead of 0xA7 for Inverted.)

This looks like an entirely sensible chain of commands for initial startup, aside from the two gaps: command 0x8E and parameter 0x08 for command 0xDB. The datasheet I have is rev 1.9 dated May 2008, so it’s possible those commands were added later. Even though they didn’t quite line up with the datasheet, these matches are too close to have been a coincidence. I’m now convinced there is a SSD1305 (or very closely related derivative) controller inside this OLED module.

Three more commands round out the end of the startup sequence:

  • 0xB0: Set Page Start Address to 0.
  • 0x00: Set Lower Column Start address to 0.
  • 0x10: Set Higher Column Start address to 0.

After these are sent, the Command/Data line was raised signifying data transmission. A large number of zeros followed, then the C/D line was lowered in for another trio of commands:

  • 0xB1: Set Page Start Address to 1.
  • 0x00: Set Lower Column Start address to 0.
  • 0x10: Set Higher Column Start address to 0.

Followed by another large chunk of zeroes, and this repeated for all eight pages of memory. Documentation section 8.7 Graphic Display Data RAM (GDDRAM) gave a size of 132 x 64 bits divided into eight pages. By that math, there should be 132 bytes in each block of zeros, but I’m not going to count that by hand. There’s probably a way to count inside Saleae Logic software, but I went with a low-tech approach:

  1. Zoom into the trace so one large block of zeros span majority of my computer monitor.
  2. Using a ruler, I measured the physical width on screen of the first eight decoded bytes of 0x00: they are 33mm wide.
  3. 132 bytes / 8 bytes = 16. So if there are 132 bytes in the block of zeros, they should be (16 * 33mm =) 528mm wide.
  4. I measured the entire block, 525mm wide. Close enough!

Having learned this information about initial startup including clearing the screen memory, I can better interpret the data captured by the logic analyzer during my other test activities.

Second Try with FormLabs Form 1+ Display Board Signals

One lasting memory I have from the movie Apollo 13 is the line “is this an instrumentation problem or are we looking at real power loss?” When an instrument tells us something is wrong, it’s possible the problem is in the instrument and not in the system it is measuring. I thought of this when I looked over the initial set of logic analyzer traces of data sent to an OLED display module. The traces superficially resembled SPI, but with many traits inconsistent with SPI. Before I dive into a rabbit hole of trying to figure out strange data, I wanted to make sure it isn’t an instrumentation problem.

The first thought was sampling rate. I gathered information for 8 channels because I had an 8-channel logic analyzer. But there’s a tradeoff. Sampling frequency drops as number of channels go up. For the base model Saleae Logic 8 that I have, polling all 8 channels drops it down to 25MS/s (25 million samples per second.) This might not be fast enough, because SPI peripherals could go all the way up to a clock rate of 50MHz. My first round of probing found only three wires with interesting activity, so dropping sampling down to 3 channels let me increase sampling rate to 100MS/s. Which is the minimum requirement to capture a 50MHz signal, but I doubt this OLED is running that fast. If this is a SSD1305 controller, its datasheet (Table 13-4 Serial Interface Timing Characteristics) lists a clock cycle time minimum of 250ns which translates to a maximum clock speed of 4 MHz. I figured even if it isn’t a SSD1305, it likely operates at similar speeds.

The next step was to redo all physical connections. I disconnected all eight probes and reconnected to reseat just the three channels I care about. I switched to a different USB cable for the Saleae, and I plugged it into a different computer that had two advantages: (1) it had a faster processor, and (2) I could connect to an onboard USB port. (I didn’t need a USB hub.)

This second set of traces look more like the SPI signal I expected, so my problem was indeed instrumentation. But the white line (channel 0, display input pin 3) is still clearly not an SPI chip select signal, as data transmission occurs both at high and low levels. What might it be? Looking into the SSD1305 datasheet, I saw its SPI mode required an extra pin labeled D/C#. This is the Data/Command control pin telling the OLED how to interpret incoming SPI traffic. If this line is low, SPI traffic will be interpreted as commands. If this line is high, SPI traffic will be interpreted as data. This could explain what I see, but for final confirmation I will examine the data to see if it’s consistent with SSD1305 communication.

First Look at FormLabs Form 1+ Display Board Signals

I’m working to understand the OLED dot matrix display from a broken FormLabs Form 1+ laser resin printer. It is hosted on a FormLabs custom circuit board and, after tracing through copper traces of that board, I have a candidate list of five wires for further investigation. When I went to attach my Saleae logic analyzer, I decided to attach probes to all eight unknown wires. (Out of ten wires total and I have identified two: the ground and 3.3VDC Vcc wires.) It wasn’t much extra effort and I was curious if anything was going on. I then captured traces for four activities:

  1. Power-on: when I plugged the 24VDC power supply into the printer.
  2. Startup: when I pressed the front panel button to start its logo animation, ending at the “lid is open” warning.
  3. Steady: Several seconds when the display stays at “lid is open” warning, with no updates.
  4. Ready/Open/Ready: Using a magnet, I toggled the display from “ready” to “cover open” and back to “ready” again.

Trace for “Steady” showed no activity at all. I had expected the system to refresh the display periodically regardless of update activity, but I just captured five seconds of silence. This is quite a contrast from the super chatty display from an AT&T CL84209 handset where I had 2569 messages within 10 seconds! Here I have nothing. Well, at least that was out of the way.

Trace for “Power-on” and “Startup” was interesting because it captured activity on two of the three wires that were unused. One looked like clock and another looked like data, so I asked Saleae Logic to treat them as I2C. They came back as valid I2C messages.

write to 0x48 ack data: 0x01 0x00 
write to 0x48 ack data: 0x00

Hypothesis: printer mainboard has an I2C peripheral bus and it’s been routed all the way to the OLED display module circuit board. I2C is not used by this particular display module, but the design gives FormLabs an option to switch to an I2C display module without changing the rest of printer hardware. In the meantime, a logic analyzer connected to the display module would see traffic on the I2C bus. By this hypothesis, such traffic is intended for other components instead of this display, so I’ll ignore it until/unless I discover a reason to revisit. [UPDATE: I found a NXP LM75B on the mainboard, an I2C temperature sensor that could answer to address 0x48.]

Back to the five wires of interest: three wires showed activity correlating with screen updates. I didn’t see any activity independent of screen update, so these wires might be a dedicated peripheral data line. If it is a peripheral bus, every other peripheral on the bus stayed quiet during my test set of activities. At first glance I thought this was SPI, but a closer look revealed behavior inconsistent with SPI.

  • Mainboard cable pin 3 — connected to logic analyzer channel 0 (white line) — showed infrequent level changes near the start of every activity. A good candidate for SPI “Chip Select” or Enable, except data transfers seem to happen both when it is low and when it is high. Which shouldn’t happen if it is indeed Enable.
  • Mainboard cable pin 4 — connected to logic analyzer channel 4 (yellow line) — shows regular level changes during every activity. A good candidate for SPI Clock, except the candidate data line changes within each “clock” pulse” which shouldn’t happen if it is indeed clock.
  • Mainboard cable pin 6 — connected to logic analyzer channel 5 (green line) — shows level changes at irregular bursts. A good candidate for SPI Data, except it pulses out of sync with “clock”.

If this is SPI, why does it look weird? If this is not SPI, what is it? I’ll have to check over my setup and try again.

FormLabs Form 1+ Display Board Routing

I’m working to understand the OLED dot matrix display from a broken FormLabs Form 1+ laser resin printer. Thanks to FormLabs user forums I have a lead on an OLED module that might be using the same OLED display. However, the OLED is hosted on a different circuit board. Publicly downloadable information exists for that board, so I will use it as a guide in my exploration.

On the printer mainboard, next to the DISPLAY label for this connector is a number 1. The closest pin appears to be system ground and the red wire in the ribbon cable. I will use that as the starting point for display input pin numbering.

Examining the front, I could see there’s a connection between pin 1 and majority of copper on this side of the circuit board, giving us a generous ground plane. The copper trace connecting to pin 2 is wider than any other on this board. It measures 3.26V DC when the system is powered up, making it the best candidate for power input. It feeds into the network of components mounted on this circuit board, which then has its own traces to the OLED. This is strongly suggestive of a power-related circuit. I measured those traces and found a few different higher voltages. Conclusion: these components implement a voltage boost converter.

Out of remaining eight wires in the ribbon cable, it seems like only five are used. Those five signals were routed together towards the OLED.

This diagram captures what I could determine by visually following traces of copper. On the other end of these traces is the sheet of yellow FPC. It has “1” printed on the right and “24” on the left, so I’ll happily use them as pin numbers. Using that system, I have a first draft for the OLED wires on that yellow FPC. Right to left in the above picture, they are: [UPDATE: added information from deciphered pinout.]

  1. NC (Not Connected)
  2. GND (Ground — connected to display input pin 1)
  3. GND
  4. NC (Only wire to visibly end inside the FPC.)
  5. 3.3V — connected to display input pin 2
  6. GND
  7. GND
  8. Display input pin 7 [UPDATE: SPI Chip Select (Active Low)]
  9. Display input pin 5 [UPDATE: Reset (Active Low)]
  10. Display input pin 3 [UPDATE: Command/Data Select]
  11. GND
  12. GND
  13. Display input pin 4 [UPDATE: SPI Clock]
  14. Display input pin 6 [UPDATE: SPI Data In (there is no SPI Data Out)]
  15. NC
  16. GND
  17. GND
  18. GND
  19. GND
  20. GND
  21. 9.0V supplied by boost converter
  22. 8.1V supplied by boost converter
  23. 12.6V supplied by boost converter
  24. NC

This explains the majority of wires going into this OLED module, leaving five unknowns that connected input IDC ribbon cable directly to OLED FPC. Those five wires will be the focus for further exploration and my Saleae logic analyzer will give me some insight as to what’s going on.