MOD NOTE: Split from a hijacked necropost:

http://forum.allaboutcircuits.com/threads/false-trigger-in-a-555-based-on-off-circuit.67016/page-2

Hi all,

Apologies for opening the issue again but I still have false triggering problem even I've tried your suggestions. It seem better after connecting a cap between 2&6 to ground and changing voltage from 5V to 12V but I still have problems. I have 250 circuits in my hand already assembled

Now have a big headache! They will be used in a hospital with a wired hand terminal but sometimes lighting or even a hand touch triggers. I am sure its somewhere from switch input side.

I dont care start-ups but false triggers making me crazy.

Your help will be much appreciated!!!

 

Hi all,

Apologies for opening the issue again but I still have false triggering problem even I've tried your suggestions. It seem better after connecting a cap between 2&6 to ground and changing voltage from 5V to 12V but I still have problems. I have 250 circuits in my hand already assembled

Now have a big headache! They will be used in a hospital with a wired hand terminal but sometimes lighting or even a hand touch triggers. I am sure its somewhere from switch input side.

I dont care start-ups but false triggers making me crazy.

Your help will be much appreciated!!!

Used in hospitals? For what, electroshock therapy?

 

Used in hospitals? For what, electroshock therapy?

No i dont want to kill people . Its just for lighting controlled from hand terminal (button).

 

Post a schematic and a picture of one of the boards. Is there a pattern to the false triggering?

 

Hi,

Attached you will find X0001.jpg (original produced) and X0001_revised (which I made revisions shown in Green color).

It seems it is working much more better now.

False triggerring was in different ways before:

- once switch wires not connected (open)
- once touching to wires by hand
- once an electrical appliance are turned on/off

Revised circuit seems much better now but I am still afraid

 

And I removed R5 resistor and LED

 

You aren't using a timing capacitor. What is the purpose of the timer?

 

Toogling relay on each button press

 

You're probably getting a spike in your voltage divider when the relay switches and it became less sensitive when you increased the supply voltage to 12V.

Do you have a decoupling cap on the timer power pin? You might also try one on the control pin.

Is the connection to B1/B2 a mechanical switch?

I built a timer circuit that controlled a mechanical relay and I couldn't get it to work because switching the relay affected the timer. I switched to a SSR and put the circuit with the mechanical relay aside...

 

How far are switch contacts from the ckt.? Are you using shielded twisted pair cable? Might reduce R2 & R3 to 2k or even 1K.

 

Thanks to all, it seems problems solved with the updates shown above.

Customer is happy with the changes.