Monday, 16 December 2013

Custard Pi 7 - Hardware Hackers interface to the Raspberry Pi

This post presents information about the Custard Pi 7. This has relay and open collector outputs, 8 bit general purpose pins that can be programmed as inputs and outputs, 4 analogue inputs and 1 analogue output and an LCD interface. It also has a prototyping area which icludes layout for a SMT IC. All of this is provided using the I2C interface which leaves all the rest of the pins on the GPIO to be used for other purposes if required.

Here is an overview of the board layout.

The prototyping area is shown below.

Relay and Open Collector outputs

This is provided using the MCP23008  8-port I/O expander which works on the I2C bus.
This is followed by the Darlington Driver, the ULN2801 which drives the relays and provides the 4 Open Collector Outputs. There are 6 LEDs which indicate the status of these outputs.
The 2 spare pins of the MCP23008 are used for the 2 key inputs from the on board switches.

LCD Interface

This is provided using the MCP23008 8-port I/O expander which works on the I2C bus.
A 2 x 16 character display has a 16pin connector on a 0.1 inch pitch and can easily be connected to the Custard Pi 7 with a ribbon connector.

8 General Purpose Digital I/O

This is provided using the MCP23008 8-port I/O expander which works on the I2C bus. All the pins can be individually programmed as outputs or inputs.

Analogue outputs and inputs

This is provided using the PCF8591 8-bit AtoD DtoA convertor which works on the I2C bus. There are 4 inputs and 1 input provided by this IC.

There are 3 powering options.

#1 The Rpi and the Custard Pi 7 can both be powered from the Rpi 5V supply. In this case jumper J14 is on the left hand side and the board 5V and the Rpi 5VPI are both connected together. Make sure that only the Rpi 5V supply is connected.

#2 Both can be powered from the board 5V. Same as above but make sure that only the board 5V is plugged in.

#3 Both are independently powered. In this case make sure that jumper on J14 is on right hand side.

Software functions

These are provided for all the blocks on the board and can be downloaded from the website.


The Custard Pi 7 is a hardware hackers dream. It will allow the Raspberry Pi to be used in many appliactions where a LCD display, relay outputs, analogue and digital I/O is required. If any fucntion needs to be added, then the prototyping area in the middle allows this to be carried out quickly.


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