Design Revisions: BenchBuddEE

A list of possible changes for subsequent boards…

  1. Correct the MCP3901 Footprint. Should be SSOP instead of TSSOP.
  2. PTC for the fan circuit is located bottom side directly under where Q4 is topside.
  3. Move components so they don’t interfere with the Arduino power plug or USB connector
  4. Move the 317/337 combo so the heatsinks can be fixed to the board
  5. Fix the NPTH size of the potentiometer footprints
  6. Add descriptive silkscreen to the Arduino footprint. It’s a pain going back to the schematic each time to remember which one is MOSI :). My custom board has the descriptions of what theArduino pins are (ie Digital 7 or Analog 1), but it would have been better to use the benchbuddee nomenclature, FAN_MODE, LDAC, etc. Best would be both.
  7. Descriptive silkscreen for the terminal block.
  8. Increase the inductor spec: only rated for 105mA
  9. FE_V of 10V doesn’t meet 3V dropout requirement of LM317/337
  10. Voltage adjust resistors don’t guarantee minimum load requirement of LM317/337, consider something like 240R and 1.3K for 8V FE_V, 1.5K pots
  11. Remove R14 and 3.3V from power switch, ATX PS_ON is a 5V signal, should never be connected to 3.3V rail
  12. Fix MOSI/MISO pins. Currently swapped.
  13. Add diode to protect +5V pin
  14. R11 and R13 at the instrumentation amp should be size: 1206
  15. Add crystal and load caps for MCP3901
  16. Connected MCP3901 REFIN- to GND
  17. Headers for easy attachment of probes
  18. Move SPI to the ICSP header
  19. Move FAN_MODE to a different pin to allow serial monitor and PWM mode. Suggest using Digital 3 for PWM_MODE and just grounding the LDAC input to the DAC.
  20. Silkscreen the pot footprints to identify V+ and V- adjust.
  21. Add a power led to indicate ATX power supply being on.
  22. Add additional spacing between V+/V- pots so that larger diameter knobs can be attached.
  23. Shrink the overall size of the board, possibly by removing the Arduino footprint altogether and instead switching to a standardized header.
  24. Q4 should have proper heatsink
  25. Add at least one momentary switch to the board to allow changing operational states on demand, rather than using “delay()” in our test code. One of the digital pins would have to be sacrificed. For example, DAC Pin 6, SHDN, could be tied directly to 5V.
  26. Switch all traffic over to the SPI bus. This would allow us to move to an abstracted interface not necessarily tied to the Arduino. We would still need to send back other pins and would need to use a SPI bus expander (SPI->single output at a time).
  27. Correct the positioning of the 1KΩ and 3KΩ resistors for the power monitoring voltage dividers on the schematic.
  28. Add another OpAmp to invert the V-_ADJ_MON signal to positive signal for Arduino analog input 1.
  29. Use a larger footprint for the inductor in the LED driver circuit (L4).
  30. Change caps for DAC and ADC from 1µF to 10µF.
  31. Add a pull-down resister to the LED_EN_PWM signal to keep the output of the AP5726 off when the Arduino pin is not defined as an output and set low.