Driving a vacuum fluorescent display (VFD) requires multiple power planes: we needed 2.5V AC for the filament, 30V DC for grids and segments, and 5V DC for a voltage bias between filament and grid/segment as well as driving all electronic logic. In our first test, these three power planes came from three different sources, for an unwieldy mess of three power plugs going to three transformers feeding into our circuit.
While we were working on debugging our control system logic, we also worked on consolidating the power supplies. From the start our 2.5V AC came from a AC transformer that was extracted from the same device we salvaged our VFD from, so we knew it was capable of supplying all the other power planes as well.
Using the same transformer to provide our 30V DC was relatively straightforward, but we had trouble with our 5V DC plane that took some head-scratching. We eventually determined the 5V DC plane couldn’t supply enough power to all the components on the plane because we had our priorities backwards: the highest amperage draw device (the Raspberry Pi 3) was furthest from our 5V voltage regulator when it should have been the closest. Our 5V power sagged to a little over 4V when our Pi was desperately trying to suck enough power through our convoluted nest of wires.
Unfortunately, while trying to move our 5V supply closer to the Pi, we made a wiring error and destroyed the regulator. Oops! Fortunately, these MP1584 modules were very inexpensive and it wasn’t a big deal to bring in a replacement. We just had to wait for a follow-up SGVHAK work session. [Emily] found enough room on our prototype PCB to fasten the regulator with a few soldered header pins so the module doesn’t have to dangle on wires. In hindsight we would have rearranged our layout to make sure there’s room for this regulator, but this is why we build prototypes.
Now our regulated 5V DC supply is first connected to the header pins that supply power to our Raspberry Pi, and from there to the PIC, before finally putting a voltage bias on our filament. This makes far more sense than the other way around, and gave us an electrically reliable system all fed from a single transformer.