Funky – Power Optimization

To increase the battery life of the little Funky wireless node I tried reducing the clock frequency of the ATTiny to 1MHz (internal 8MHz + CLKDIV fuse) but when set to 1MHz no communication was possible. With support from the JeeNode Forum I now know that for proper operation of the RFM12 a clock frequency of at least 4MHz is required.
As the current consumption in standby was measured to be about 50uA with a cheap digital volt meter and the DHT11 datasheet states an even higher standby current of min. 100uA for the sensor, “CapnBry” had a nice idea of reducing the power consumption by switching the DHT11 on and off via a port pin. As the DHT needs about 1 seconds after power on to deliver trustworthy measurement results one simply could sleep 1 second short, power on the sensor, sleep for another second, measure the result, turn of the sensor and transmit the data before going to sleep again.

I will test this procedure within the next days and keep you up to date…

Update 1:
Due to the minimum voltage requirement of 3V for DHT11, it is not possible to switch the sensor on and off using a port pin when running from 3,3V.

Update 2:
I bought some 1F/5V supercaps and charged one to 3.6V. The funky could run more than 16h from it reporting the temperature and humidity every 5 minutes. After that 16h the voltage dropped below 3V so the temperature and humidity could not be measured but the funky kept communication for about another 6h. So with a 1F super cap charged to 3.6V the funky can live for about 24h.

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