Problem the 555 get triggered when i power up circuit

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The discussion revolves around a 555 timer circuit that triggers unexpectedly upon powering up due to a connection issue. The user is advised to remove capacitor C3 from pin 3 to prevent false triggering, but this solution did not resolve the issue. It is suggested that a pull-down resistor on the trigger pin could help, as the current setup may be causing the 555 to trigger when the power is applied. Additionally, a power-on reset circuit is recommended to hold the trigger low during power-up. The conversation highlights the importance of circuit design in preventing unintended activation of components.
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I am connecting a Not and And gate to an activation switch (S1 or S2) that trigger a 555 to turn on a motor using a relay , i am using a main power up toogle switch that power the 555(vcc of 555 is sensor1) , so when it is off the 555 can't be triggered ,my problem is that everytime i turn on the toogle switch ( connecting 5 V to Sensor1) , the 555 get triggered alone and one cycle is run , attached is the circuit , and gate and not gate are connected to 5 V before the toogle switch is in position of sensor1...

Any ideas of how to fix it ?

Thanks
 

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Are you using the 556 as a monostable? If so, I think I know what causes this.

Try removing the capacitor C3 on pin 3. This is not necessary and it causes a delay on the lower two 5K resistors and you get a false triggering, just on turn-on.
On a 555 this is pin 5 and you do the same thing.
 
Yes i am using the 556 as monostable, i will try what you said , i let you know , thank you for your quick response...

abril
 
unfortunatelly i just tried that and it did not work , i took off the C3 and keep auto triggering when i put the toogle switch in position of sensor 1 :frown:

any other idea ?

Thank you
 
Pull down resistor on TRIGGER_555

edit: currently you have a pull up on trigger_555, thus during power up it will turn HIGH first.
 
Looks to me like you are triggering the 555 when applying the 5volt Vcc. (which is what ShadowPho1 suggested) Ususally one would have a power-on reset circuit of some sort. In this case, I whould hold the trigger low for a time while the power supply comes up. Not quite sure why you are using the switch for test/sensor.
 
Your monostable circuit is fairly standard.
see:
http://www.eleinmec.com/article.asp?4

You could try removing the trigger input to the 556 (temporarily) to see if it still triggers on startup. It may be getting a pulse from earlier in the circuit when you turn on.

Leave C3 disconnected, though. It does cause this effect.
I had a camera being used for aerial photography which was being driven by a 555 monostable and it was taking a very expensive photo of the runway every time it was turned on. Removing this capacitor, which is always shown in circuit diagrams, fixed the problem.
 
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