Design Revisions: I2C and SPI Education Shield

A list of possible changes for subsequent boards…

  1. Done 18-AUG-2014 Rev: Move the temp sensor from being located over the ATmega328
  2. Done 18-AUG-2014 Rev: Spread the LEDs out a bit.
  3. Done 18-AUG-2014 Rev: Move all bottom side components top side so small batch assembly houses can build it.
  4. Done 19-AUG-2014 Rev: Connect the buttons to available pins so that they can be used long term as well. Three hardware-debounced buttons would be valuable.
  5. Done 19-AUG-2014 Rev: Make the 74HC595 available in all sketches so that bitwise operations can be visualized on the LED array.
  6. Done 18-AUG-2014 Rev: Modify battery backup circuit for the MCP7940N to match the appnote.
  7. Done 19-AUG-2014 Fix: Increase the pad size for the SOIC16 footprint, see if the SOIC8 is a good guide.
  8. Done 18-AUG-2014 Fix: Add test points / pads / header
  9. Done 19-AUG-2014 Fix: Change MCP3008 bypass cap to 1uF, as per datasheet.
  10. Done 18-AUG-2014 Rev: Move the VREF silk screen so its more visible.
  11. Rejected Rev: Consider putting an LDR or pot on the board with a jumper to give something to measure with the ADC out of the box
  12. Done 18-AUG-2014 Fix: Change signal at the U4 level shifter, currently MOSI and SCLK are mixed – A1 -> B2 A2 -> B1.
  13. Done 08-NOV-2014 Rev: Change the GND pad for the battery holder to a larger physical space to ensure good contact with the battery.
  14. Rejected Rev: Remove Test Points.
  15. Done 08-NOV-2014 Rev: Remove 0Ω jumper resistors.
  16. Done 09-NOV-2014Rev: Add a pullup resistor for the Temperature Sensor Alarm pin.
  17. Done 09-NOV-2014Rev: Add a jumper to allow control of the shift register OE pin.
  18. Done 09-NOV-2014Rev: Add 10uF cap at +5V