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connecting two monostable 555 timers..

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normad

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hey guys.. i want to connect two monostable 555 timers so that the pulse out of one would trigger the other..

as suggested by you guys in my last thread i tried connecting them through capacitor which is set at vcc.. it works on simulation but somehow when i made the circuit it didnt trigger :(

so is there any alternate method of doing it?

would bringing the capacitor voltage closer to the trigger voltage using a voltage devider help?

i used a 1nf capacitor.. must i use a smaller capacitor?
 
This should work. Post your circuit. You likely have something else misconnected.
 
hmm.. ok i spent bit more time on it..

View attachment timer..asc
heres the circuit..

ok this is what happens.. when i trigger the first 555 the first led goes on but on its timeout the second one doesnt trigger..

but when i take off the first led the second one triggers in the right time.. and the same happens for the third..

is this because the leds diode beaviour? would using an op-amp instead of a transistor fix this? how must the gain of the op-amp be set in such a case?

and if your wondering why i didnt check with some other load i culd only find leds in the lab :S
 
hmm.. ok i spent bit more time on it..

View attachment 41272
heres the circuit..

ok this is what happens.. when i trigger the first 555 the first led goes on but on its timeout the second one doesnt trigger..

but when i take off the first led the second one triggers in the right time.. and the same happens for the third..

is this because the leds diode beaviour? would using an op-amp instead of a transistor fix this? how must the gain of the op-amp be set in such a case?

and if your wondering why i didnt check with some other load i culd only find leds in the lab :S

hi nomad,
You MUST have a current limiting resistor in series with the LED's, limit the LED current approx 10 to 15mA.
 
hey eric :)

i see.. i tried putting a 100k resistor in series with the base but it didnt work.. you're saying i should put the resistor between the emitter and the led yeah? hmm.. but if you're using this circuit to drive a motor.. wouldnt the resistor effect the motors power?
wouldnt an unity gain op amp work? because it has very high input impedance? and if i used an op-amp the negative power supply is not necessary is it?
 
and how would a darlington couple work for this?

hi,
I will modify your asc file so that one 555 triggers the next [ with an LED]

Back in a few minutes.

EDIT:
Run this Sim in LTS. I have modified the circuit.
I have shortened the 555 delays for testing only, put them back to what suits you.

timer01..gifView attachment timer...asc
 
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