A remote-controlled ON-OFF switch with just 3 components

A few months ago, I was building circuits with the 555 timer. It has a mode where you can get a long pulse out (for example 1 minute) from a very short pulse (for example 1 microsecond). So you can for example build a light switch that automatically turns off the light after a certain time, to save energy. ​ Anyway, I wanted to create a remote-controlled ON-OFF switch for an electronic candle I have. And since I was into the 555 timer, it made perfect sense to use it to convert all those tiny pulses from a remote control into one long pulse that would toggle my candle, via a flip flop. It worked nicely and I was happy. Today, however, I came across a circuit that used only one chip, a decade counter (CD4017), to do the same thing. Looking a bit closer, I realized the decade counter was used as a flip flop that toggles. But no 555 timer. Instead, there was a capacitor and resistor to convert all the tiny pulses into one long pulse. And a transistor to invert the pulse. Huh, I thought to myself. That was smart. But why not use a flip flop? And why not use a negative-edge triggered flip flop to not have to invert the pulse? So I simplified the design to just a capacitor and a flip flop: ​ I hooked it up on a breadboard. Connected the output up to my relay module, and it worked! ​ ​ Keep On Soldering! Oyvind @ build-electronic-circuits.com PS! Wherever you are on your journey, if you want to improve your electronics skills - here are two ways I can help you learn electronics: ​Ohmify​ is for people like you who are interested in electronics and want to learn skills like soldering, circuit design, Arduino, and circuit board design - while also building practical projects along the way. ​ ​Get the eBook ​Getting Started With Electronics​: A short and beginner-friendly eBook I wrote to help people get started. It contains clear and simple instructions to get started building electronics. If you're new, this is the perfect place to start.

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