středa 4. února 2015

Low power success!

A brief update. After fixing the problem with uploading the code to that CR2032 powered sensor node, I took some power consumption measurements today. I was pretty disappointed to find out the average consumption to be around 15mA, compared to 4uA what I saw yesterday. The difference was due to attaching the nRF24L01 module. It turned out that the RF24Network library does not put the module to sleep mode (as it might need to route the traffic). After manually forcing the module to sleep with Radio.powerDown (), the power consumption went down to expected levels - 7uA! I still need to tweak it a little bit and see how it performs, but I am one step closer to the goal!
I also need to review and test the wake up sequence of Arduino. I am guessing that the fuses are set to slowest wake up. As Arduino draws some 5mA when operating, I have to keep this wake up as short as possible. Other things to do are adding a real temperature sensor, and battery measurement circuitry... and fix a bug with reading node ID from EEPROM (hardcoded to 8 bytes).
I received some samples from Linear today, namely the LT1307 step-up switcher. I tried that on a breadboard, and I am disappointed. It works, sort of, but doesn't even power a LED. I know that breadboard isn't a good test platform for 600kHz switcher, but still... Time to put it on a piece of PCB, and experiment with some inductors.
I'll need a good way to measure the efficiency. As I don't have four multimeters and all the cables, I need to think about something else.

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