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Electronics => Projects, Designs, and Technical Stuff => Topic started by: themacman33 on March 03, 2014, 05:11:59 pm

Title: 555 timer circuit triggered by drill?
Post by: themacman33 on March 03, 2014, 05:11:59 pm
I have built a 555 based timer for my analog soldering iron. When I used my drill on the same power strip as the circuit and power through the relay to the outlet, the circuit triggered. I can't seem to figure out how this happened. Can anyone explain how this works, and how to fix it without changing the drill to another outlet?
Thanks, Mac
Title: Re: 555 timer circuit triggered by drill?
Post by: uwezi on March 03, 2014, 06:09:29 pm
Where does the Vcc of your NE555 come from? A power drill is a nasty device when it comes to introducing spikes on the mains - if your Vcc is not properly filtered it can do anything with your timer.

Place some decent electrolytic (probably 1000 µF or more) and some 100 nF or bigger ceramics capacitor between Vcc and Gnd. Additionally you might want to use a net filter on the primary side of your power supply.
Title: Re: 555 timer circuit triggered by drill?
Post by: themacman33 on March 03, 2014, 06:18:49 pm
The power comes from a 12v DC wall wart on the power strip. I will add the filter cap, thanks!
What is a net filter? I've never heard of that...

Thanks!
Title: Re: 555 timer circuit triggered by drill?
Post by: uwezi on March 03, 2014, 06:27:47 pm
Quote from: themacman33 on March 03, 2014, 06:18:49 pm
What is a net filter? I've never heard of that...

I probably used the wrong term, what I meant is a line filter (http://en.wikipedia.org/wiki/Line_filter)
Title: Re: 555 timer circuit triggered by drill?
Post by: themacman33 on April 07, 2014, 12:04:39 am
The resistor did in fact work. Thanks!
Title: Re: 555 timer circuit triggered by drill?
Post by: calexanian on April 07, 2014, 02:42:32 am
8 meg ohm resistor and a 470uf cap? Does it ever time out? I would thing the leakage of the cap alone wound keep the thing going for ever. Also are you using the CMOS version? Much more susceptible to noise.