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LED working during only 3 seconds after pressure

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SamTech12

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Hi,

I have a switch that work the same way the carpet of Dance Dance Revolution work. So when there's a pressure on the switch, it's working and without pressure, it doesn't work. I need to have a little LED working during approximatively 3 seconds after the pressure has been released on the switch and the LED isn't working the rest of the time. Someone know how I could do that?? :-?

Thanks a lot
 

Yeah I've effectively used a 555 Timer, but I need a very short pulse to have my LED working during 3 seconds after pressure, if not, the LED stay alight. My purpose is to have the lowest consommation.
 

It doesn't matter how long you will push the button switch as long as the switch is opened before the 3sec elapse (in your example)

Alex
 

Another simple way to add turn-off delay to an LED circuit is to use a RC delay.
This RC circuit is placed in the base of a BJT transistor.
The transistor has control of the LED. First we use the switch to charge the capacitor and to maintain the capacitor charged for all the time it’s closed.
Later it takes some time for a capacitor to discharge through a resistor. The time is determined by T = R x C, where R is the resistance in ohms, C is the capacitance in Farads and T is time in seconds. The value of RC is actually the time it takes for the capacitor to be discharged to 63 percent of the supply voltage. More details here:
Capacitor Discharging

If we use a transistor the time increase as the voltage on capacitor need to be lower than the minimum Vbe=0.6V
 

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