Ned Kelly Lamp

I didn't make the whole lamp, just the stuff stuck to the bottom. And just because it's neatly hidden away underneath doesn't mean it's importaint. It's not! The lamp worked fine without it... but it wasn't used much...until now. Now it has been made vibration sensetive - the status of the lamp is changed whenever it detects vibration above a threshold. In laymen's terms, to turn it on or off you simply chuck something at it. Almost anything will do - a book, a coin, a mobile phone. Anyone (with reasonably accurate aim) can turn off the lamp without even getting up.

It uses a speaker mouned to the base as a low frequency microphone. Signal form the speaker is amplified by an op-amp  in a positive, low pass config. The pot (next to the transformer) is part of the feedback circuit and is used to control the op-amp circuit's gain and hence the sensitivity threshold. The output of the opamp goes to a transistor + RC (time constant of about half a second) circuit to 'debounce' the signal. Then on to a schmitt trigger to clean up the rise/fall times and then to the clock input of a D type flip-flop (with /Q tied to D to provide a toggle) and finaly to an opto-coupler which drives a triac to do the AC switching.

27/12/05