Timer. What's wrong

[Karl Gega]

I have projected this timer and built it.

But the output stays always High, i don't know what's wrong with it?

The cap is 2200uF and the resistor is 10k. I have also tried with a 100uF cap but still no change.

Any help?

View attachment 37081

 

[David Bridgen]

Pin 2 needs to be "pulled up", so connect a resistor from it to the positive supply.

 

[Karl Gega]

Still the output stays high.

 

[David Bridgen]

Hmmm .....

The switch on the trigger pin is a momentary action one?

The circuit looks fine otherwise (with a pull up on pin 2).

 

[Karl Gega]

Yes  the switch is a momentary action one.

It is possible that the IC has gone bad because in the beggining i changed  the power
wires by mistake (connected ground to Vcc snd Vcc to ground ) and IC heat up so much that it couldn't be touched with hand (it might have remaind in that state for two minutes).

Should i replace it? Or it is ok.

Thank you for your time.

 

[David Bridgen]

Ah.  Yes Karl, replace it.

 

[Karl Gega]

I have done all the changes suggested here and came to this one.

I will build later.

View attachment 37096

 

[audioguru2]

Hi Karl,
With the diode across the relay coil backwards, the 555 IC will burn again. I mentioned other necessary changes in your other topic. ;D

 

[Karl Gega]

What about this one?

View attachment 37110

 

[audioguru2]

The diode across the relay coil (in parallel) is still backwards.

 

[Alun]

I've corrected it for you.

 

[Karl Gega]

Thank you Alun