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CD4017 counter

The CD4017 is a decade counter and there are a billion or so circuits based on a 555 timer feeding into the counter with the output being a lovely array of LEDs lighting up in response (think KnightRider). Halfway through breadboarding the circuit I came over all bored and went looking for something else to do with the IC. Scrolling down the list of possibilities on a search for alternatives I chanced on a "clap switch" which looked pretty cool.

After building the circuit it soon became evident that you had to be a champion clapper to make it work. I mean what's the point of a clapper circuit if you have to be right next to the microphone and clap like a demon to activate it - you might as well just lean over and flick a switch!

What followed was a few hours of happy transistor swapping. Firstly I tried four (!) SS8050 NPN transistors wired cascade style to increase the gain. It was (only slightly) better but I still got sore hands from clapping. Each SS8050 has a Hfe around 250-300 so I swapped out to a BC517 darlington which jumped up to a ridiculous Hfe around 25k - and it seemed no better as a clap switch.

It occurred to me based on a previous experience with electret microphones to swap out the 100k resistor recommended in the circuit diagram for a trimpot and fiddle with the resistance to affect the sensitivity or gain of the sensor.

At a resistance of around 20k the rig was working pretty well, but as a card carrying perfectionist I then changed out the standard electret microphone for a fancier model which includes it's own crude gain control and voilà, a stupid clap switch.