Powering a relay/capacitor circuit

[Guest]

I have been reading about keyboard emulation, and have a question. Is it safe to power this type of circuit with any ordinary 5 volt power supply that comes out of the wall? I'm not an electronic genius. After wall power has been converted to 5V DC and .3A, can this present a fire hazard or danger of electricution?Thanks, any info is appreciated.Ken

[Guest LeoL]

OK, I'll try and answer this one. I've done some dangerous things electronically in my life and I can safely say you won't be starting any fires this way unless you wire up with the polarities reversed...and even then, I've done worse.;)The only thing you need to worry about is filtering the output voltage of your wall adapter. Since the keyboard uses the voltage supplied by the PC and is already filtered, so it won't have any filtering circuitry onboard.Try it out on an old KB if you have one. It's worth a try. If it doesn't work then wire up a couple of large value caps (1000uF 15-25V) for rough filtering. This might do the trick.If not then you'll need a voltage regulator and an RC filter as per the VR spec sheet.Hope this helps.-Leo