# Any ideas to measure Frequency of a AC source?

Anyone there have any idea or webpage that could guide me on measuring frequency of a ac source of Vpp 5v?

Here's a circuit designed to measure 12VAC and also power the Arduino from it:

http://ruggedcircuits.com/html/circuit__21.html

It won't work for powering the Arduino in your case if all you have is 5VAC (unless it's 5Vrms in which case the peak voltage is 7V and may work if you don't draw a lot of current and C1 is appropriately sized).

The idea is you use pulseIn() on the digital input to measure the wave-to-wave period and from that you compute the frequency.

-- The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected

Could always just look at it with an oscilloscope. www.dpscope.com

Or a soundcard 'scope, depending on the frequency. Visual Analyser 2010 http://www.sillanumsoft.org/

Was there something you wanted to do with that measurement?

What range of frequencies are you wanting to look at. If it's quite a narrow band, say +-50% around a centre frequency and the waveform is sinusoidal then you could simply use an RC series circuit and measure the voltages developed across the R (Vr) and the C (Vc). Since you are using a series circuit, the current Irc through both components is the same. Vr = IrcR Vc = IrcXc Note however that Vr and Vc are out of phase with each other. Google RC series circuit and you'll find the necessary explanations of how to compute C.

Jack