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FEZ Hydra - Best Way Measure DC and AC Voltages


Hi All,

I was wondering about the best and safest way to measure Voltages on the Hydra? Say from 0 to 30V.

I have seen a few ways to do it but really thought it best to ask the experts first.

All the Best



I am not an expert, but voltage divider + ADC is the first thing that comes to my mind.


Thanks Iamin!

I like this idea also… I cant find the ADC Pins on the schematic or any reference to them, do you know what Pins I may be looking for?

Thanks again! +1

All the Best



ADC pins on all mainboards are on an A socket. Pins 3, 4, and 5. On Hydra that is socket 13 or 14.


Thanks Brett! +1

Appreciate your quick response!

All the Best



Voltage divider will work fine for DC voltages. It will also work for AC but you will need to take into account the peak to peak voltages and the negative swings.

I assume you are measuring a DC voltage?

Handy little app if you have an Android phone or tablet is ElectroDroid. Got a nice voltage divider calculator that can even take into account the ADC input load.

Lots of over nice little handy calculators and pinouts etc.


Thanks Dave, will have a look at this.

DC but it may have ac component to it in some cases.

All the Best



Hi all

I’m trying to monitor the charging voltage of the lipo rider pro with a fez hydra. In the circuit above the 5,1V zener will protect the mainbord in case of excessive tension on the measured pin, right? Shouldn’t this value be something like 3,3v? At the specs the hydra analog inputs are rated 3,3V max. Will they accept 5,1V without damaging the board?



That schematic was just an illustration, you need to adjust all values. And yes, you should use <3.3V zener diode.



Another question… Do i need do connect ground pin of the voltage divider to the ground pin of the A-socket that will monitor the voltage? or is internally grounded so there is no need for that? In other words… do i need to connect 2 wires (V+, V-) to the A-socket or just 1 wire (V+)?



It depends on where do you get V+, if it is from the same motherboard - then one wire is enough, if from different source - then two wires (V+ and GND) are required because you need to have a common ground.