RFM95 CAD mode demo pt. 1

Описание: Demonstration of CAD mode of the Semtech SX1276 / RFM95 Lora module.

CAD mode is described in the datasheet of the chip (both in the RFM and in the Semtech version of the datasheet). Because I couldn't find any software examples that implement CAD mode, I decided to try to implement it myself. All the necessary info to implement CAD mode can be found in the datasheet.

I made some minor unpublished changes to the arduino-LoRa library (https://github.com/sandeepmistry/ardu.... My working solution is interrupt based. I change the mapping of DIO0 and DIO1 between CadDone, CadDetected and RxDone, RxTimeout as needed.

To achieve most power savings, the challenge is to initiate the CAD mode only as often as is needed to realistically be able to detect part of the preamble. At SF7 the CAD detection takes about 1.9 ms (one symbol is 1 ms). When the preamble is longer, the interval of successive CAD modes can be decreased: More power savings.

Furthermore both the microcontroller and RFM95 must be put to sleep whenever possible. One challenge are the short sleep durations. For example in the video the delay / sleep before the next CAD mode was around 4.6 ms.

Result: Current at 3.3 V of both Pro Mini and RFM95 was around 3 mA. Preamble of sender was set to 12.

Reference power consumption without CAD mode: 14.4 mA (of which 2.5 mA for the Pro Mini)

Hardware:
Pro Mini with 32 kHz watch crystal in asynchronous mode
RFM95

Software:
sdrangelove
inspectrum

pt. 2:    • RFM95 CAD mode demo pt. 2: 100 uA