DC to AC inverter with the 555

[iambrus]

Hello there, I found an interesting DC/AC converter design for 50HZ 220V.
http://www.uoguelph.ca/~antoon/circ/555dcac.html<p>I was almost very happy until I read the description. There is R4 potmeter which is supposed to regulate frequency. Without an oscilloscope how can figure out what frequesncy I have? I guess there is no way.

[bridgen]

You could power a record turntable, assuming it has a synchronous motor, and adjust the frequency until the reproduced audio sounds right.

[iambrus]

Thank you David, I went through the circuit and realised that I only need to leave out R4 in order to get a fix 50Hz frequency.