Oversensitive 555 monostable multivibrator

[batvink]

Ok, firstly I was daft enough to think I could jump back into electronics after 10 years! <p>I have the circuit mentioned above, it's being used on a "buzzing wire" game to make a long buzz every time the wire is touched.<p>The trigger (pin 2) is held high by way of a 100pF capacitor, the voltage is 9V. It's triggered by touching the wire and allowing the capacitor to discharge through you.<p> The problem is that is goes off all the time by bizarre acts such as walking past it - must be static.<p> The question - how can I desensitise this circuit? Any help is greatly accepted.<p>I have tried using a resistor (1K) in series with the trigger, but this stopped it working completely.

[Buford]

What are you doing with pin 5?

[batvink]

Pin 5 is sat there twiddling it's thumbs, doing nothing.<p>This is a kit I bought to simply solder together. You can see the full details here...<p>PDF document<p>Oh, how I wish I'd kept my hand in at electronics!<p>[ November 18, 2003: Message edited by: batvink ]</p>

[greg123]

Tie pin 5 to ground through a 1 nF cap.<p>greg

[russlk]

I suspect you are using the CMOS version of the 555, the bipolar one would not work. But, in either case, leaving the input open is to invite trouble. The 100 pF cap will not hold the trigger high, you need a resistor, 10 meg or 100 meg. Touching the trigger wire at this time of year (dry high static) could blow the 555 input.

[batvink]

Russ - is the resistor in place of the capacitor, or between pin 2 and my trigger? I'm hoping you're talking about replacing the capacitor, I tried a resistor on the trigger wire and it compltetly stopped it from working.