Change: Interface PCB

Dev Kit PCB installed on a Pi 2.

Background

A Printed Circuit Board (PCB) has been designed and manufactured. This is an interim solution - a step towards the goal of a complete turnkey system.

• All sensor plug in.
• 12 VDC power supply with battery voltage monitoring

The goals were to

1. make it quicker and easier to build a system and to make it more reliable.
2. to establish a relationship with a board house.
3. to select an open source pcb layout package and learn how to use it.
4. to test the footprint of the RJ connectors and mating with the Pi.

Problems

1. ADC is only one channel.
2. No Real Time Clock (RTC).
3. Board does not meet Pi HAT specification.
4. Board is not general purpose but limited to our use.

Proposed change

Split this board in two, Board A and Board B.

• Board A will be a general purpose interface board that meets the Pi HAT specifications and contains:

1. at least one 4 channel ADC so each load cell will be individually measured instead of being summed.
2. Real Time Clock with battery backup.
3. Configuration ROM
4. Power supply

• Board B will have all the connectors installed in a bulkhead configuration. It will connect to Board A by directly plugging into a header on Board A or connect via a ribbon cable.

Design Considerations

1. Minimum of 8 (4 differential) inputs.
2. Must have reliable serial communication to the Pi. Probably should use SPI, I2C bus.
3. Consider using 16 bit ADC instead of 24 bit.
4. Conversion speed (samples per second).
5. Will gain of 64 work? Currently using x128.
6. Extra ADC channels.
7. Extra GPIO pins.
8. Channels individually configurable.