Mixing and Matching Custard Pi’s
Introduction
If a particular Custard Pi does not have all the right inputs and outputs, then it’s possible to combine more than one. This post looks at the various combinations that are possible.
For more examples click here to go to the blog post
GPIO bus connection method
The various cards use different means of connecting to the Raspberry Pi GPIO and this summarised below.
SPI bus | I2C bus | 8 digital I/O |
Custard Pi 2 | Custard Pi 6 | Custard Pi 1 |
Custard Pi 3 | Custard Pi 7 | Custard Pi 2 |
|
| Custard Pi 5 |
The card combinations are limited by the type of bus connection used. For example, the SPI bus can only address 2 devices. As the Custard Pi 2 has a Analogue to Digital Convertor (ADC) and a Digital to Analogue Convertor (DAC) and both of these use the SPI bus, you cannot have more than 1 Custard Pi 2 connected to the GPIO. Because the Custard Pi 3 also uses the SPI bus, you cannot have a Custard Pi 2 and a Custard Pi 3 connected to the Raspberry Pi at the same time.
The I2C bus is addressable and you can have as many I2C devices as there are addresses. This means that you can have up to 8 Custard Pi 6’s connected at the same time. You just have to make sure that the switches on each card are used to set a different I2C address.
Example 1 - 64 relays controlled from the Raspberry Pi
Eight Custard Pi 6 cards daisy chained to provide a total of 64 relays that can be controlled from the Raspberry Pi GPIO.
Example 2 - 8 relays and 8 analogue inputs
This is achieved by using a Custard Pi 6 and a Custard Pi 3. As one uses the I2C bus and the other uses the SPI bus, this is possible.