## 555 Pulse Generator Circuit

This is a pulse generator with adjustable duty cycle made with the 555 timer IC. The circuit is an astable multivibrator with a 50% pulse duty cycle. The difference from the standard design of a 555 timer is the resistance between pins 6 and 7 of the IC composed of P1, P2, R2, D1 and D2.

The diodes D1 and D2 set a definite charging time for C1 which produces a 50% duty cycle in a normal case. The duty cycle (n) is dependent on P1 and P2 in the following manner:

n = 1 + P2/P1

If P2 = 0 (n = 100%) then the frequency can be approximately calculated with the following formula:

f = 0.69/((2*P1 + P2 + 4.7kΩ)*C1)

## Pulse generator circuit diagram

**Printed circuit layout of the pulse generator**

**Components List**

C2 = 10µF

C3 = 0.1µF

R1 = R2 = 4.7K

D1 = D2 = 1N4148

IC = 555

C1, P1 and P2 must be calculated