NE555: ON/OFF function with NE555

Hello,

I'm unable to see your schematic. Can you upload using the "Insert/Edit Media" button.

Best,

Katlynne Jones

oups here is the schematic. Sorry

Hello,

You can try adding a smaller (.1uF) supply bypass capacitor in parallel with the 47uF cap to help with high frequency noise. Is the button normally open, or normally closed? If normally closed, the capacitor C1 may be discharging when the metal case is touched which would put a low voltage on the Thr/Trig pins and trigger the timer. 

Best,

Katlynne Jones

Hello,

The problem remains despite the bypass capacitor in // with the 47uF. The push button is normally open.

Thanks for your feedback

Hello,

Please also try adding a 0.1uF cap between the Trig/Thr pins and ground. 

For clarification, is the timer circuit in the same metal case that the button is fixed to?

Is the metal case floating relative to the timer supplies?

Best,

Katlynne Jones

Hello,

The capacitor beetwen Trig/Thr do not improve the behavior. The timer is in the same metal case that the button is fixed to.The metal case is floating relative to the timer.

We do suspect that the parasitic capacitor beetwen the switch and his internal contact might be the issue.

Any recommendation there?

Thansk

Hello,

Did you add the capacitor between the Trig/Thr & ground as shown below? Not between Trig & Thr.

The added capacitor of  0.1uF should be much larger than the switch's parasitic capacitance.

You can try grounding the case to the Gnd in your circuit.

Best,

Katlynne Jones

Yes this was the try. Let's see the results grounding the case

Thanks

Hello,

Hopefully that will work for you. I look forward to hearting the results.

Best,

Katlynne Jones