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Simple Pulse Generator

This circuit is used to provide positive going pulses. The pulse width varies from 10µs to 100 ms at the rate of 20 pulses per second to 1 pulse per second and adjusted by a 1 MΩ potentiometer. Transistor T1 and T2 form a relaxation oscillatory circuitry. The frequency of oscillation depends on C1 and VR1. The pulse width is varied by a 47KΩ (VR2) potentiometer. Any required pulse width range is selected by the switch SW1 below

circuit diagram of pulse generator

Position of switch SW1 Pulse width
1 10 µs to 100 µs
2 100 µs to 1 ms
3 1 ms to 10 ms
4 10ms to 100 ms
PARTS LIST
Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)
R1 = 33 Ω
R2 = 47 K Ω
R3 = 47 Ω
R4 = 33 Ω
R5 = 2.7 KΩ
VR1 = 1 MΩ LOG
VR2 = 47 KΩ LIN POT.
Capacitors
C1 = 1 µF/16V
C2 = 0.0022 µF
C3 = 0.022 µF
C4 = 0.22 µF
C5 = 2.2 µF/16v
Semiconductors
T1 = SL100
T2 = SK100
IC1 = 74121
Miscellaneous
SW1 = 1 pole 4 way switch

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