I need a simple way to build a circuit that would receive an input pulse and output a pulse after a period of time. A better way to describe it is like the lights on a cell phone, when you press a key the keypad lights up and after a period of inactivity the lights go off. Thanks for any help.

 

hi craigc,

what you need is a 555 timer ic operated in the monostable mode, or if not you can also use small signal transistors.

with a little patience try browsing thru this forum and you can find the circuit diagram of both suggestions.

i could not for the moment post diagrams, my scanner has gone kaput :cry:

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im doing a project regards 'auto fish feeder'...for tht i need a long period which can set such tht can turn ON feeder motor 5hrs once, or 4hrs once...please if anyone can guide me..its will be great.

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hi kumar,

what i can suggest to use for that long period of 4 to 5 hours is a programmable timer ic. its the CD4536. you can program that for as long as 37 hours.

Am sorry i cant post the schem without the permission of the author, besides my scanner has gone kaput. even if you will e-mail me privately, still i cant.

There maybe some guys in the forum who might have the schem for that ic.

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As Mozikluv suggested 555 could be connected as a monostable pulse generator as shown in my schematic. Here the monostable timing period is initiated by a falling edge (i.e.a high to low transition) applied to the trigger input (pin 2). When such an edge is received and the trigger input voltage falls to below 1/3 of the supply voltage, the 555 output (pin 3) goes high and the monostable pulse is generated for a period determined by the time constant C X R. The amplitide of the pulse will be approximately equal to the supply voltage. The period for which the out put is high is = 1.1 RC. Hope you understand

Cheers !

Attached Images

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