There was a time within the latest previous when many within the DIY electronics neighborhood regarded down their noses at microcontrollers and particularly at growth boards. “Why use an Arduino when you possibly can simply use a 555 timer?” they might ask. Virtually talking, the reply is fairly apparent: microcontroller growth boards are simpler, supply much more flexibility, and are sometimes cheaper besides. However we nonetheless love seeing what folks can obtain with discrete parts and easy ICs, corresponding to Urs Schmidt controlling an RGB LED gentle strip with previous CRT TV elements and 555 timers.
This undertaking started when Schmidt discovered a damaged CRT (Cathode-Ray Tube) TV in entrance of his home. It was principally unsalvageable, however it did have an attention-grabbing 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 regulate 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 colour channel on the LED strip. You will need to notice that it is 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 commonest option to management the brightness of LEDs digitally — as a result of it isn’t attainable to regulate voltage straight — 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 possibly can 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 colour 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 (particularly resistor and capacitor proportions). The 556 is identical factor, however with two timers on one chip. Collectively, they’ve three timers—one for every colour. 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 heart beat width and frequency, brightening or dimming the corresponding LED colour channel.
This can be a frequent option to management RGB LED strips, however we like Schmidt’s use of the previous TV sliders for enter. Now he has a novel option to set the colour and brightness of his workbench LEDs.