I would like to follow fluctuations of the mains frequency (50 Hz, yes, I know they are very low) in the lab, without a connection to the wall socket. I suppose it should be some kind of antenna (capacitive one?), amplifier and comparator to create and output a TTL signal corresponding with the mains frequency.

Did someone try this? Will it work? My concern is that moving in the room will affect the shape of the signal.

  • 3
    \$\begingroup\$ What is the reason for dismissing a more direct coupling to mains? \$\endgroup\$
    – jippie
    Commented Dec 1, 2013 at 22:20
  • \$\begingroup\$ Interesting thought. Your power supplier will correct their frequency against a standard and have a record. Maybe you can access it online. \$\endgroup\$ Commented Dec 1, 2013 at 22:50
  • \$\begingroup\$ Equipment that should be synched with the mains is a battery powered one. \$\endgroup\$
    – user33510
    Commented Dec 1, 2013 at 23:04
  • \$\begingroup\$ I wonder did you ever figure out how to do this? I would like to do something similar for a different reason. I have some old master slave clocks and I was thinking of converting them to battery power and using the EM from the mains as a reference frequency. (I know I could use a crystal oscillator but I thought this might be more fun!) \$\endgroup\$ Commented Mar 25, 2020 at 10:24

2 Answers 2


The only worthwhile component of the EM wave created by AC power is the magnetic component and this is really easy to pick-up. Use a coil of wire - maybe ten turns or more with a diameter of say 10cm and then an op-amp amplifier configured as a sallen key low pass filter set at 50Hz. For added high-frequency noise immunity, put a 10uF non-polarized capacitor across the coil. If you added more turns you might even be able to get it to tune at 50Hz (or 60Hz) but you'll need an inductance of about 10 henry to do so but, using ferrite isn't out of the question.

You should be able to pick up ac power at a few centimetres.

  • \$\begingroup\$ Thanks for the answer, but I asked about measurement in the lab which is 12-15 sq.m. and I do not know where the antenna will be positioned. I agree that placing a coil near the wire will resolve the problem. Leo \$\endgroup\$
    – user33510
    Commented Dec 1, 2013 at 23:14

I do this with a length of wire going to left or right channel and on the microphone jack on a sound card or mic jack on laptop. Picks up the 50 hz no problem. Read the port with python, write a .wav file. Plot, Fourier transform. I can see that the power company adjust the frequency every half hour,

  • 1
    \$\begingroup\$ Frequency adjustment would normally be continuous and depending on the load / generation balance. It would not be changed every half-hour. What country? (You didn't fill in your location in the user profile and that information is useful in these circumstances.) \$\endgroup\$
    – Transistor
    Commented May 4, 2021 at 20:09
  • \$\begingroup\$ An alternate, related method that I have used to unintentionally monitor the mains frequency: Play an electric guitar with single-coil pickups through a high-gain amplifier. \$\endgroup\$
    – Theodore
    Commented May 4, 2021 at 21:22
  • \$\begingroup\$ I’m in Denmark. Did not know how to edit my location. Got this message: “Sorry, your request could not be completed because it looked suspicious. If you meant to perform an action on Electrical Engineering Stack Exchange, please return to the previous page and try again.” \$\endgroup\$ Commented May 5, 2021 at 21:21
  • \$\begingroup\$ Keep it simple, use a small transformer. You get the advantage of isolation and a high rejection of local noise. \$\endgroup\$
    – Gil
    Commented May 14, 2021 at 3:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.