I am designing a circuit, which use a micro controller (teensy 3.1), and various sensor.

I am aware of the sensor consumption, since it is in the specs, same for the MC; but these are theoretical values; which does not give you a real figure about how much your circuit will use.

Since I need to power the circuit with a battery, I want to know how to find out the actual consumption when the circuit is working.

Can I just grab the multimeter and measure somehow the energy used? I know the mA that each device takes; but beyond that; I am not sure about how to go for the calculation. Someone suggested me to have the ciruit to run, with a fully charged battery; measure the operation time and then calculate the value based on the capacity of the battery

Example: 1200mAH last for 1h, the circuit use 1200mA; if it last 10h the circuit use 120mA.

This makes sense but I can't believe that this is how professionals actually measure consumption.

  • \$\begingroup\$ Take the worst case values from datasheets. use them for calculating required time with battery.. \$\endgroup\$ – user19579 Nov 12 '15 at 6:24

Get your circuit working and then turn off the power. Put your meter into current mode; the 200 mA scale is probably sufficient. Put your meter in series with your circuit by attaching the red lead of meter to the power supply, the black lead of meter to the input of your circuit, and the negative lead of your circuit to the power supply's negative terminal. Apply power; you will see the actual current usage of your circuit. Without circuit details I can't know the consumption, but I bet it will be 50 mA or less. Watch it as you operate all of the circuit's functions to see if the demand changes with different activities.

When you choose a battery or power regulator for your circuit, make sure it's rated higher than the minimum to account for surge at power-on and other power spikes. 500 mA would probably be good enough for a circuit like yours, but that's just a guess.

There are all kinds of complexities that can change things; if you are using motors, power consumption can go much higher than when the circuit is still, and there are other issues. But that is too complex for this conversation.

  • \$\begingroup\$ Thanks a lot Dan; it is a good way to start! My circuit at the moment has a temperature sensure, a pressure sensor (both connected via I2C), a teensy and a bluetooth module. I am not planning to use any motor. the circuit mostly work for home automation; giving info about the temperature and humidity, so the computer can adjust the thermostat accordingly. Since it is a continuous communication via BT, I am trying to figure out the battery capacity that is most likely appropriate for the circuit \$\endgroup\$ – rataplan Nov 12 '15 at 6:44

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