# Peripherals power usage

I am trying to measure the power usage of a Raspberry Pi peripheral, say a temperature sensor, and compare it with wall power input to the Raspi. Is there a device that measures the power a peripherals uses?

• Just to clarify for others, when you say "power" do you mean Wattage? Or volts? Jul 6 '16 at 4:17
• I mean.. if he has anything other than 3.3v on the Pi then he will have a serious problem. So yea.. he want to measure how much Power (W) the temperature sensor is using. Feb 26 '19 at 7:35
• Just in case you missed it in the lower comments. Ohms law `amps (A) X volts (V) = power (W)` Feb 26 '19 at 7:46

Your measurements depend on how you have everything connected. Lets assume you are using the GPIO pins. Using figures from the original Pi they say a MAX of 16mA per pin and a total MAX of 51mA for all pins.

So the answer is easy. The maximum Power (W) your temperature sensor will use is `16mA (0.0016A) x 3.3v` is `~0.005w`

But then again you can just look up in the product technical sheet what current it is rated for. Really.. you should have checked before just plugging it directly to GPIO.

The last way to do it is like they taught us in school. Use a multimeter that has Amp mode, wire it in series and it will show you the amps. And yet again using ohms law - amps X voltage = watts (power)

• That isn't ohms law ;-)
– Ingo
Feb 26 '19 at 18:44
• The real definition is too complicated for anybody to understand. But fair enough. It’s based on ohm’s formula Feb 26 '19 at 19:04

I do not think the pi can do this on its own. You would have to use a separate module that can be hooked up to it to do so. But all component/module datasheets do come with a standard in use and not in use power consumption. You can easily time the usage and such and make a database or by other means record it. then, simple make some calculations.

• datasheets contain information about Amps drawn when in various states. In this case on and off.. but like GPS modules have several power states. Some things can handle variable voltage input but then the datasheet tells you the internal voltage used.. which is typically now a days 3.3v.. sometimes 5v for IC type things. Ohms law (this is getting boring) `amps (A) X volts (V) = power (W)` Feb 26 '19 at 7:45