transformer tester

I was reminded that a simple 555 timer can create an astable oscillator that can be used with a DVM to measure a transformer windings when at a rally or when there are no markings.

The values for R1, R2 and C1 will give you the frequency and the duty (charge/discharge).

t1 = 0.693 (R1 + R2) x C

and

t2 = 0.693 x R2 x C

Where, R is in Ω's and C in Farads.

You might then follow that with a simple op amp integrator to turn the square wave into a sine wave.

Or another option without the op amp so a similar small component count is a saw toothed oscillator.

The frequency of the circuit is:

f = (Vcc-2.7)/(RxCXVpp)

Vcc is the supply voltage and Vpp is the Vpp of the output voltage.

 

The transistor can be almost any GP PNP.