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Hi: I want to build a wattmeter based on a Pi Zero (to reduce costs in the final version, maybe I can use a Pi3 to develop it. Can you tell me if this is possible, based on what I need to do? I need to measure power in realtime used by a computer. My idea is to insert the Pi based power meter in between the power cable of the computer and the computer itself. For what I saw, I understand that I need the Pi, a Voltage Divider (I ignore exactly which one or where to buy one) and... anything more? The idea is to power the metering device from a free USB port in the computer and I have to think how to access the data stored in the Pi (I have to upload it every minute to a database).Can you be kind enough to explain this to an ignorant like me? Thanks!JP

If you are measuring the input to your computer then I would assume that would be an AC power line. For measuring AC I would recommend using the iSnail current sensor which has an output of 0-5V. This can be connected to our ADC Pi Zero board to measure the voltage and convert this to the current being used. We have used the iSnail sensor on our own projects before and it is the simplest way of measuring AC power.

An alternative which would use lower-cost parts would be to use an Arduino board and a CT current sensor and with a few passive components you can use this to capture the data from the sensor and it would output as a serial device to your host computer via the USB interface. There is an example of this on https://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface