Detect 120VAC

Thread Starter

Stupdiav

Joined Jul 29, 2011
10
I have seen multiple discussions on determining the presence of AC power. Most revert back to Current Monitoring for logical reasons. In my case I can not guarantee that there will be current flow. I have looked at relays, but I am concerned about the size of all the units that I am finding, the coil life and the heat generated from the coil. I have also been looking at Solid State Relays but am having trouble finding any that do 120VAC input smaller than a brick. The load is only 5VDC and is driving an input of my micro controller, minimal current.

I am at a loss on how to accomplish this. Any help is much appreciated.
 

TeeKay6

Joined Apr 20, 2019
567
I have seen multiple discussions on determining the presence of AC power. Most revert back to Current Monitoring for logical reasons. In my case I can not guarantee that there will be current flow. I have looked at relays, but I am concerned about the size of all the units that I am finding, the coil life and the heat generated from the coil. I have also been looking at Solid State Relays but am having trouble finding any that do 120VAC input smaller than a brick. The load is only 5VDC and is driving an input of my micro controller, minimal current.

I am at a loss on how to accomplish this. Any help is much appreciated.
@Stupdiav
If you have access to an isolated (i.e. from a transformer) AC voltage (e.g. part of your power supply), say 24vac, for most microcontrollers you can simply drive an input pin via a large resistance (to limit current into the pin). That is, most CMOS microcontrollers allow a small voltage/current overdrive on the I/O input pins (generally several mA); at the worst, you can use signal diodes (1N4148), or a low power zener (1/2W), to clamp/limit the voltage at the input to the range from ground to the microcontroller's positive power.
 
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