Hello collegues
As maybe not all of you have the possibility to accurately measure the power consumption or power output of your RF module, I thought to post the following information.
Node is a Atmega1284P custom board (GitHub - IoTDevicesCH/LoraMidiAtmega1284P: Small Lora(WAN) board using an Atmega1284P chip and RFM95 module) with RFM95 module. Node is transmitting every ~300 seconds. Two v2 gateways are in the same building.
An OTII ARC with programmed output voltage at 3.75V to simulate an Li-Ion battery powers the node and RFM95 module through an LDO with ultra low quiescence current.
With LMIC v4.0.0 and TTNv3 with ADR enabled, it looks like this.
Power consumption for uplink is with MCU power usage but without RX1/RX2, so only TX message. Payload is 15 bytes. Power consumption includes everything after ‘LMIC_setTxData2’ and takes about 120ms until the transmission ends. Transmission datarate is SF7 BW125 @ 868MHz.
- the transmission power is reduced after 62 uplinks (per uplink power consumption 8.92µWh)
- the transmission power is reduced again after 20 additional uplinks (per uplink power consumption 8.48µWh)
- the transmission power is reduced again after 20 additional uplinks (per uplink power consumption 5.85µWh)
- the transmission power is reduced again after 19 additional uplinks (per uplink power consumption 4.88µWh)
RSSI with full TX power is on the first gateway -50 and SNR 10.25.
RSSI with full TX power is on the second gateway -65 and SNR 10.80.
RSSI after the first TX power drop is on the first gateway -56 and SNR 10.25.
RSSI after the first TX power drop is on the second gateway -65 and SNR 9.8.
RSSI after the second TX power drop is on the first gateway -56 and SNR 9.5.
RSSI after the second TX power drop is on the second gateway -67 and SNR 10.
RSSI after the third TX power drop is on the first gateway -59 and SNR 7.5.
RSSI after the third TX power drop is on the second gateway -67 and SNR 10.20.
RSSI after the fourth TX power drop is on the first gateway -62 and SNR 10.25.
RSSI after the fourth TX power drop is on the second gateway -69 and SNR 9.50.
Unfortunately I had my measurement tool open only for 128 uplinks… so maybe it would drop even further. If there is interest for this kind of topic, I may test it for more than 128 uplinks and report back with some additional results.
You can clearly see, that the power consumption for the uplink message decreased by nearly 50%. Also, the peak current cleary dropped from about 120mA to 65mA.
Please keep in mind that this is no professional measurement but was a simple test from my side to see, if ADR really drops TX power (and therefore power consumption) for battery driven projects.
