RFM69CW Power Consumption

Following on from my post on RFM12B power consumption here's the same measurements for the RFM69CW (see RFM69CW intro blog post).

Current consumption was measured in the same way as explained in the RFM12B post back in July 2013. Voltage drop was measured across 10R current shunt resistor.

A fully populated emonTx V3.4 with a 433Mhz RFM69CW running discrete sampling code with a single CT connected was used in the test. The V3.4 was powered directly with 3.3V DC from bench PSU.

emonTx V3.4 with RFM69CW Test Setup

Test setup illustration

Test Bench
Please excuse my photos of the scope traces rather than screen captures, for some reason the USB socket on the scope did not seem to be working today :-(

Full sample and RFM69CW transmit trace capture

When an AC-AC adapter is not connected the emonTx goes to sleep in between readings. The above current trace shows the ATmega328 waking up for 295ms to sample from one CT channel the spike at the end is the RFM69CW transmitting. The trace below is a zoomed in capture of the RFM69CW transmission and LED. 

RFM69CW transmission current consumption 
The current trace above shows the RFM69CW transmission: 33mA @ 3.3V (109mW) for 4ms. The current spike at the end (up to 39mA) is the emonTx LED. In this test the emonTx was running the standard discrete sampling firmware transmitting a JeeLib packet structure with six integers. Since we were only sampling from one CT four out of the five integers will be zero. 

This equates to a 15 bytes payload plus 9 byte overhead @ 48kb/s. See JeeLib packet structure

In comparison I measured the RFM12B to consume 25.5mA @ 3.3V (84.2mW) for 3ms.

My measurements pretty much agree with the datasheets, here's a comparison table compiled by Low Power Labs:

Even though the RFM69CW does consume more power while it's transmitting it does have a lower sleep consumption than the RFM12B. This increased transmission power should result in an increased transmission range.

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