As discussed in a previous blog post the iC880a is a LoRaWAN concentrator that can be used to create a gateway. The iC880a only provides the LoRaWAN hardware, it does not provide any processing capabilities, for this we use a Raspberry Pi. However, the Raspberry Pi and the iC880a have different pin layouts for their connector. This means that an adapter is needed to convert between formats. One approach is to use simple jumper cables to link the two PCBs which was used for one of the earlier gateways. We have also tried using stripboard to create the converter board, but this did not cope very will with deploying outside (the tracks oxidised). The best approach is to use a purpose built PCB. There are already some open source adapter boards available, and we used one early on in our experiments but these did not have the features we wanted so we set about building our own.
The features that we wanted the PCB to have are as follows:
- Header and bolts to enable a Raspberry Pi to be firmly attached.
- Header and bolts to enable an iC880a to be firmly attached.
- Mounting for a battery backed RTC to provide a constant time source.
- Mounting for a temperature/humidity sensor.
- Connection between the PPS pin on the iC880a and the Raspberry Pi.
- Connection from the optional ublox GPS module on the iC880a to the Raspberry Pi
- Connections for an Adafruit Ultimate GPS module.
- Connections for the chipset from an Adafruit Ultimate GPS directly
We have now completed the PCB and have been using one in one of our LoRaWAN gateways for a few months, and we used a second at EMF to provide LoRaWAN coverage. The designs for these boards known as Pi-Cot (Pi Concentrator on Top) are now freely (CC-BY-SA) from https://github.com/computenodes/pi-cot. The designs are provided as is, if there’s something yo would change please fork and issue a pull request.