Controlling RGB LEDs with Outdated CRT TV Components and 555 Timers



There was a time within the current previous when many within the DIY electronics neighborhood regarded down their noses at microcontrollers and particularly at improvement boards. “Why use an Arduino when you may simply use a 555 timer?” they might ask. Virtually talking, the reply is fairly apparent: microcontroller improvement boards are simpler, provide much more flexibility, and are sometimes cheaper in addition. However we nonetheless love seeing what folks can obtain with discrete parts and easy ICs, equivalent to Urs Schmidt controlling an RGB LED light strip with old CRT TV parts and 555 timers.

This venture started when Schmidt discovered a damaged CRT (Cathode-Ray Tube) TV in entrance of his home. It was largely unsalvageable, nevertheless it did have an fascinating management panel consisting of a number of sliders for adjusting quantity, brightness, distinction, and extra. Schmidt beloved the look of these sliders and determined to make use of them to manage RGB LEDs that illuminate his workbench.

Schmidt’s plan was to make use of three of these sliders, with every one controlling the brightness of a single coloration channel on the LED strip. You will need to word that this can be a standard RGB LED strip and not an individually addressable RGB LED strip like NeoPixels. One slider would alter pink brightness, the opposite inexperienced, and the ultimate would management blue.

The most typical option to management the brightness of LEDs digitally — as a result of it isn’t attainable to regulate voltage instantly — is to modulate energy in a short time to decrease the common voltage. That is known as PWM (pulse-width modulation) and is why you may usually see LEDs flashing in movies. A microcontroller can produce an arbitrary PWM sign based mostly on firmware utilizing an inner clock. However Schmidt didn’t wish to use a microcontroller, so he wanted one other option to generate a variable PWM sign for every LED coloration channel.

To realize that, Schmidt used a 555 IC and a 556 IC. The 555 is a timer with an output frequency and size decided by enter traits (specifically resistor and capacitor proportions). The 556 is similar factor, however with two timers on one chip. Collectively, they’ve three timers—one for every coloration. The management sliders are actually simply linear potentiometers, so adjusting these adjustments the worth of the brink and set off resistors (they’re equal on this case). That concurrently alters the heartbeat width and frequency, brightening or dimming the corresponding LED coloration channel.

It is a widespread option to management RGB LED strips, however we like Schmidt’s use of the outdated TV sliders for enter. Now he has a novel option to set the colour and brightness of his workbench LEDs.

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