measure 24V AC with emonTx V2 Shield

I want to detect 24V AC with the EmonTX V2 Arduino shield. I have no plan to use the 9V AC adapter to measure voltage, so I could use the existing voltage divider for the 24V input. Should I replace one of the resistor with a different value in the voltage divider, or can I just feed 24V into the 9V AC input ? I only need to detect ON/OFF 24V, so I don't need to have a full range of analog values between 0 and 24.


Robert Wall's picture

Re: measure 24V AC with emonTx V2 Shield

If you feed the "9 V" (actually it's around 11 V) with 24 V, you will clip the inputs and you will not get an accurate measure of voltage. By far the best is to increase the 120 kΩ to 150 kΩ, then the input won't be overloaded and relying on the protection diodes; and you can if you want later get an accurate measure of it.

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.