Follow the Schematic and PCB design guide when making a module.
The I2C bus from the core module will provide your board with 3.3V. If you need a voltage other than 3.3V, you can either step up the supplied voltage or use your own battery. Nevertheless, the ground pin must be connected the ground on your module.
Every module must contain two matching 4 pin headers for the I2C bus. Modules will be daisychained via their two I2C headers starting from the Core module.
- Pin 1 – Vcc 3.3V – this pin should be connected directly to the same pin on the other header, regardless of whether the 3.3V supply is used in your module’s circuit. If it is being used on your circuit please note that it has already been regulated.
- Pin 2 – I2C SCL – should be connected to your chosen microcontroller’s SCL pin.
- Pin 3 – I2C SDA – should be connected to your chosen microcontroller’s SDA pin.
- Pin 4 – GND – this should be connected to your circuit’s ground regardless of whether you are using the 3.3v supply.
Your module will require these two headers at a minimum. You may wish to use extra headers for external sensors or off board components. Please use the headers provided in the Apex Eagle Library. The library contains both upright headers and headers which are at a right angle. In the Apex Library, the headers you need are under:
22-?-<size> and are listed as