PCB Rev 1.0 Errata:
- Diode D3 is reversed in the board silkscreen. Place it backwards (opposite of what is shown) for a positive supply, and normal (as shown on the silk screen) for a negative supply. Rev 1.1 has been changed to be correct.
- Crystal X1 is rotated 90 degrees on the board silkscreen. Instead of placing it with the long side oriented up / down, place it with the long side oriented left / right. Rev 1.1 has been changed to be correct.
- There is a problem with the ISP circuit, which prevents you from programming a bootloader (or flashing fuses, or doing anything with the ISP) when the AVR plus all components are on the board. Please program the bootloader and flash fuses (using the script in power_supply/bootloader/program.sh) prior to soldering the entire circuit. You can do this in one of two ways: either program the chip prior to placement (if you have some sort of removable TQFP socket), or solder the AVR + crystal + 8pF caps and then program it, and only once the bootloader is programmed do you finish soldering the rest of the circuit. UPDATE: In the latest iteration of the Rev 1 controller, I have decided to not solder the encoder pullups / caps / TVS directly to the board; rather, I will solder it to the encoders themselves (which can then be detached from the board using the jumper cables). This allows ISP to work properly when the encoders are unplugged. Rev 1.1 has been changed to have jumpers to disconnect the encoders, so the supporting hardware can just stay on the board.
- The current limiting LED indicator light does not turn on properly. Current limiting works, but the indicator light does not. To fix it, connect pin 6 of op amp U2 to a -3v source rather than GND. Two resistors (20k and 5.1k) in a voltage divider across the -15v supply works fine for this. See this log post for more details and a picture of how I did this.
Use PCB Rev 1.1 to fix all four of these problems.
When soldering up the negative channels, be sure to reverse the polarity of the following components:
- All three diodes
- Both electrolytic capacitors
- Both status LEDs (the + side of the LED should go to the pin marked GND)
You also need to populate the 0-ohm resistors in the NEG board areas (rather than the POS ones).
Of course, you also need to ensure that V+ is connected to VB and V- is connected to VA when soldering the power inputs.