This is a toggle switch to momentary (latch to push button) switch converter. Most of the time we need momentary to toggle switch. But sometime we need to convert some latch signal to momentary signal. This circuit base on 555 timer IC and it uses monostable mode.

Parts List C1 0.1µF Ceramic C2 10µF 25V Electrolytic C3 0.1µF Ceramic C4 10µF 25V Electrolytic C5 0.1µF Ceramic R1 47kΩ R2 47kΩ R3 10kΩ R4 1kΩ D1 1N4148 D2 1N4148 Q1 2N3904 RL1 Relay (voltage same as supply voltage) IC1 555 Timer IC

The Monostable 555 Timer circuit triggers when negative pulse applied to pin 2.This negative pulse need to go down 1/3Vcc. Once triggered, the 555 Monostable will remain pin 3 output on until the time period (T) set up by the R1 × C2 network has elapsed.

T= 1.1 ×R1 × C2

T in seconds, R in Ω and C in Farads

T=1.1 × (47× 1000) × (10/1000000)

=0.517 ≅ 0.5 seconds

When the switch is closed C3 capacitor will charge through the SW1 and R2, Because the voltage at pin 2 move below 1/3Vcc. Then 555 triggers and start timing cycle. The output at pin 3 immediately moves up to near the supply voltage and remains at that level until the C2 timing capacitor charges to about 2/3 of the supply voltage. When the switch is open, the C3 capacitor discharges through the R2 and R3 resistors. The D1 across the R2 prevents the voltage at pin 2 from rising above the supply voltage when the capacitor discharges.

Update: Toggle to Momentary Switch Youtube Video

Update 2: Toggle to momentary switch PCB









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