Keep in mind that the changes are occurring at 10 Hz, so there’s bound to be some residual charge in the on-board capacitors of the RFM12B module.Īnyway. But there’s an intriguing split in the curve – this is most likely caused by a different current consumption when VCC is rising vs when it is dropping. Because it really doesn’t matter how we vary VCC over time. Here’s what happens when the input signal is switched to a sine wave:Īs expected, the essence of the curve hasn’t changed one bit. It’s essentially the same picture as before, because the sawtooth is a straight line, and so voltage rise is the same thing as time in this case. This type of analysis can also be done using the X-Y mode on most oscilloscopes: Note that this power consumption can’t be reduced: we don’t have the ability to send any commands to the RFM12B until it has started up! As you can see, the current draw quickly rises between 1 and 2V, and then continues to increase sort of linearly. The magenta trace is the current consumption, which turns out to be 0.650 ♚. The yellow trace is VCC, the supply voltage – from 0.3V. This will have a slight effect on measurement accuracy – but no more than 2%, so I’m ok with it. So the idea is to apply a sawtooth signal to the RFM12B, rising from 0 to 3V at the rate of say 10 Hz, and to measure the voltage drop across a 100 Ω resistor at the same time.

Well, time for a test using the power booster described recently: For quite some time, I’ve wanted to know just how much current the RFM12B module draws on power-up.

Raspberry pi ribbon cable fritzing