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I'm a software engineer by trade so I'm a bit at a loss. Maybe I don't know the correct words to find what I'm looking for.

I have a Bluetooth Low Energy remote control powered by two AAA batteries. I want to monitor the power usage for the device. I understand how I can put a multimeter between the batteries and the device and measure actual power usage, in milliampere, but I'm more interested in how much power it uses over a span of time. Note that the power usage patterns differ between pairing, standby, when sending a key, etc, which is why I'm much more interested in total power used instead of only the draw at ONE moment in time.

Basically I'm envisioning something like an ampere-counter (electron-counter), instead of an ampere-meter. Which would mean that you read out on the end of the day: 20 mAh used. Does something like this exist?

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  • \$\begingroup\$ This is possible but fairly tricky. However, for a device actuated by a user pushing a button, and having AA batteries, the lifetime is likely to be extremely long unless it is used heavily. How do you plan to set the pattern of usage for a test? Or does this actually have an on/off switch? \$\endgroup\$ – Chris Stratton May 8 at 14:47
  • \$\begingroup\$ Yes, this is one of the main factors. Also I guess it would differ very much between different users how often they'll push buttons on the remote in daily use. But I think is secondary to my question! \$\endgroup\$ – MichielB May 8 at 14:49
  • \$\begingroup\$ Typically what you would do is put a sense resistor in the ground lead, put a capacitor across it, and watch the voltage drop across that on a scope. You can also do it with an MCU/Arduino as the meter. You would be looking for pulses of say 20-30 mA and a lower baseline active and a hard to measure baseline inactive. \$\endgroup\$ – Chris Stratton May 8 at 14:52
  • \$\begingroup\$ Is it integrated current (mAh) you want or integrated power (joules etc.)? Power is voltage x current. Analogue circuit integrators don't work too well when the integration time is more than a few seconds. Maybe think along the lines of a digital integrator. \$\endgroup\$ – Andy aka May 8 at 14:54
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If you want to count amperes over a fairly short period of time, and these periods of heavy use will be interspersed by periods of very low 'keep-alive' consumption, then there is a cheapskate way to get fairly reasonable figures.

Power the device with a large resistor or switch from your batteries, with a very large capacitor across the device.

Measure the capacitor voltage, press a button to activate your heavy power draw activity, and when it's stopped, measure the capacitor voltage again. The drop in voltage, multiplied by the capacitance, is the charge the device has used between voltage measurements.

You will need to do some initial experiments to make sure you have a large enough capacitor to power the whole activity with sufficiently little voltage loss that the MCU still works, but enough loss that you can measure with reasonable accuracy.

Between measurements, either wait long enough for the capacitor to recharge through the resistor, or close the switch to recharge it quickly. If you do leave a large resistor connected, then remember that this will supply some charge during the measurement period, which is easy to estimate and allow for.

As high value capacitors tend to have a very large tolerance, you can calibrate the capacitance by discharging for a known time at a known current.

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