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Building the Arduino energy monitor - measuring mains voltage and current Example


(Simon Hill) #1

I am buying the parts to build the example from this page https://learn.openenergymonitor.org/electricity-monitoring/ctac/how-to-build-an-arduino-energy-monitor

The build calls for 2x 10uF capacitors, but I’m not sure which ones to buy as they have a voltage rating as well, what voltage do I need or doesnt that matter, also, Electrolytic or Tantalum Bead?

Also, there is the 33 Ohms resistor, as I will be running at 5v arduino. I have one, but was interested to know why the The EmonPi uses 22Ω burden resistors as that is also a 5v setup?


(Robert Wall) #2

If you look at the circuit diagram, those capacitors are decoupling the 2.5 V midpoint voltage bias supply. The voltage rating needs to be greater than the voltage which the capacitor can possibly be subjected to, which is 5 V, and it’s good practise to go higher by a suitable safety margin. So 10 V (the lowest you’re likely to get) will be fine. We use electrolytic in the emonPi, emonTx and emonTx Shield.

No it isn’t - the Atmel 328P front end runs at 3.3 V.


(Simon Hill) #3

Thanks for the quick reply Robert.

So with the 10uF capacitors would some rated at 25v for example still be ok? just that I actually have a few of those already from an old project.


(Robert Wall) #4

Yes, no problem at all (as you’re presumably not constrained by size).