I am testing how low I can get the power consumption of the RedBear BLE Nano, which is a development board for the Nordic NRF51822 System on Chip that contains an ARM micrcocontroller, and BLE 4.0 mdoule.
I have produced some software that should have turned off all of the subsystems in the processor, and put the device into a sleep mode that is interrupted by a timer periodically.
This seems to work, I am powering the module form a bench supply and I have a multi-meter in series. When I have my finger touching the metal case that shields the Raytac module which is on the BLE Nano, the multimeter reads a constand 20uA, which is great. Then happily comes out of sleep mode every 10 seconds, flashes an LED and goes back to sleep, again at 20uA.
If I do not touch the metal shield, then I see this 20uA value climb to ~330uA very slowly (takes about 1-2 minutes), then descend down to ~200uA, where it seems to stabilise.
My bench supply only tells me the current draw in milliamps, so it's registering zero the whole time.
I have no idea why there is a difference when I am not touching the shielding, and whether the module is really only consuming ~20uA or closer to 200uA.
If anyone can explain which current draw is likely to be the actual one, and why there is a difference, that would be great.