View source for Change: Interface PCB

[[File:P1010016c.jpg|thumb|400px|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 

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

==Problems==

#ADC is only one channel.
#No Real Time Clock (RTC).
#Board does not meet Pi HAT specification.
#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:
#at least one 4 channel ADC so each load cell will be individually measured instead of being summed.
#Real Time Clock with battery backup.
#Configuration ROM
#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==
#Minimum of 8 (4 differential) inputs.
#Must have reliable serial communication to the Pi.  Probably should use SPI, I2C bus.
#Consider using 16 bit ADC instead of 24 bit.
#Conversion speed (samples per second).
#Will gain of 64 work? Currently using x128.
#Extra ADC channels.
#Extra GPIO pins.
#Channels individually configurable.