RGB LED Strip Dimmer With 555 Timer





Introduction: RGB LED Strip Dimmer With 555 Timer

About: I'm a mechanical and mechatronics engineer currently working towards a PhD in robotics. In my spare time I love playing soccer and tinkering with electronics!

Hi guys!

In this Instructable, I'll be showing you how to make a cool RGB LED strip dimmer using a few potentiometers and a couple of 555 timers.

I'm currently working on a larger project which involves using this circuit, but I thought it would be good to share this circuit since it's really cool to play with just by itself. The larger project I'm working on is comprised of two circuits: the RGB dimmer and a colour organ which makes the LEDs dance to the music when an audio source is plugged into the circuit. I was inspired to work on this project after posting this Instructable here which used a single colour LED strip with a dimmer and an audio pulsing circuit. After posting this, I received many comments and messages requesting to work on an RGB version of the circuit, so here is part of it, with the rest to follow very shortly.

Since I am posting this Instructable while in the process of finishing off the other project, a few of the pictures I have included here actually show parts and components from my other project build. I can assure you all however that the parts I have listed in the following step are all that you need to complete this project and I explain later when you can ignore other components that appear in my pictures.

Anyhow, I hope you all enjoy this Instructable and I'll be posting the larger project very soon! See the attached video to see what you're going to make in this project, hope you like it!!

Step 1: Gather Your Parts and Materials

You'll need a few things for this build...

Electrical Components:

1 * NE555 http://core-electronics.com.au/555-timer.html/?acc...

1 * NE556 Dual 555 timer linear IC

3 * TIP31 transistor

6 * 100nF capacitor

6 * 1N4148 diode

3 * 4.7k resistors

3 * 10k variable resistor https://www.jaycar.com.au/10k-ohm-linear-b-single... or http://core-electronics.com.au/rotary-potentiomete...

1 * variable resistor knob (red) https://www.jaycar.com.au/10k-ohm-linear-b-single... or http://core-electronics.com.au/black-plastic-knob-...

1 * variable resistor knob (green) https://www.jaycar.com.au/10k-ohm-linear-b-single... or http://core-electronics.com.au/black-plastic-knob-...=

1 * variable resistor knob (blue) https://www.jaycar.com.au/10k-ohm-linear-b-single... or http://core-electronics.com.au/black-plastic-knob-...

1 * RGB LED Strip of your chosen length. Here's what I bought (5m): http://www.ebay.com.au/itm/252554507922?_trksid=p... or http://core-electronics.com.au/led-rgb-strip-bare-...

1 * 12V 6A power supply to go with the LED Strip

Various sizes of JST connectors http://core-electronics.com.au/jst-connector-kit-2...

A bunch of wire




Soldering iron

Side cutters



Bench top vice

Hobby knife

Step 2: Prepare the Potentiometers

Solder three wires to each of the potentiometers and at the free end, add a 3 pin JST connector. I've colour coded mine: left pin black, middle pin white and right pin red. Solder them all up the same, since you want to be able to connect and disconnect to any output of the timer ICs.

Slip the coloured knobs on the ends of the pots and you're ready to start soldering the veroboard circuit.

Step 3: Solder Up the Veroboard

Take the provided circuit diagram and pin outs for the 555 and 556 timers and solder the veroboard. Remember to include three 3 pin JST connectors in your layout somewhere so you can easily plug and unplug the potentiometers.

You'll also need to include a 2 pin JST connector for the power input and a 4 pin JST connector for the LED strip. In the pictures you will notice I have a 3 pin JST at the top right of the board and a 2 pin JST on the top left of the board and some large diodes running down both sides. You won't need the diodes for this circuit and you only need a 2 pin connector for the power input. You also don't need the smaller diodes that run from the discharge pins of the 555/556 timers to the transistors. So just follow my circuit diagram which doesn't include these other components and you should be okay.

For the LED strip connector, the white wire which comes off the LED strip should be connected to 12 V, while the red, green and blue wires should be connected to the TIP31C transistors as shown in the diagram.

Step 4: Plug Everything In, Power Up and Test

Plug in your 3 potentiometers, the RGB LED strip and your 12 V power source. If everything is wired up correctly, you should be able to control the red, green and blue lines of the LED strip individually, making many different colours through different red, green and blue colour intensities!

Hope you guys liked this build and please follow me so you get to see the next stage to this circuit- adding a colour organ so the lights can also dance to the music!



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    15 Discussions

    A 4th pot "upstream" of the 3 maybe? It would limit the juice to the 3 and they couldn't get any brighter than the limit pot allowed. It's not *exactly* brightness control but it's something.

    Is it possible to add a 4th potentiometer to control overall brightness as well as color?

    1 reply

    The overall brightness is effectively controlled through those 3 potentiometers; I can't see an easy way to add in another potentiometer to control the overall brightness. If you figure out a way to do that, please let me know!

    Hi there, I've compared the two datasheets and nothing is jumping out at me which indicates you can't use the TIP120 instead of the TIP31. Please let me know if you try it out and it works the same, they seem very similar.

    Hi, I just tried and works the same, but, when i set the potentiometer to the minimum, the led still have a minimum bright. (With the 2 transistors) Why?

    Is it possible you have used a logarithmic potentiometer and not a linear one? The LEDs should be completely off at the minimum potentiometer position.

    Hi. I'm planning on using your project to make a lamp. Thanks for posting this! For clarification: so you are feeding 12V through the LEDs and the rest of the circuit is the PWM that controls the amount of current flowing through the transistor, correct?

    Thanks again, I will post photos when I finish my project. I was using cheap individual LEDs but they were nowhere near as bright and colorful as the strip is.

    4 replies

    Hi, thanks for your comment, I'm looking forward to seeing your end product!

    The 555 timers put out a PWM signal which drives the transistor here. So for your LED strip, the white wire is connected to +12V and the other wires corresponding to each of the R G B colours are connected to the collector of each of the TIP31C transistors. Basically, the PWM is triggering the transistor here and the LED strip for each colour is grounded at the frequency of the PWM signal.

    Hope that clears things up! Best of luck with your project :)

    Yes it does, thank you! I was thrown off because of the orientation of the LED in the diagram, but I understand now. One more question, what exactly are the diodes (for example D4 & D5) protecting? The potentiometer doesn't require "directional protection", but I fail to see what exactly the diodes do connected to the pot like so (I understand what diodes do in general). I greatly appreciate your time! (You explain very well).

    I've looked into this a bit and can't find any real explanation, this seems to just be a standard way to connect the potentiometer to the 555 timer. It appears in many circuits on the internet e.g. http://www.555-timer-circuits.com/led-dimmer.html

    Okay, if I figure out a possible answer I'll let you know. Thanks again, good luck with future instructables!:)

    First off, great instructable!

    Second off,I know for all purposes and means the 555 timer with all the other components should be used. However, I have been able to accomplish this before without anything but some resistors and a couple potentiometers. So I guess my true question is, what is the point of using the circuits if you can simply use 2 different pots? I have some projects coming up and I am deciding if I should use more than just some pots or not.

    2 replies

    Hi, thanks for your comment!

    I've checked out your Color Changing Wooden Lamp and it's really neat, I just added a comment there FYI :)

    If you do a bit of background research on LED strip controllers, pretty much all of them use PWM to control the brightness/colour mixing of the LEDs. Sure, you can do this with potentiometers too, but using PWM is much more efficient, since when you use a potentiometer, it's just a resistor and the excess power that the LEDs aren't using is dissipated as heat. If you're using long LED strips, you'll need more power, and thus you need to make sure that the potentiometer you use is rated for whatever power needs you have (consider that higher power requirement = larger component size = higher cost!!). If you don't design this correctly with the right components, you risk blowing out your potentiometer. Do your potentiometers in your lamp get really hot? Perhaps not, since your LED strips are quite short, but this is something to consider in your design.

    Also, with PWM you can more precisely control the dimming. You may have noticed with the lamp you made that controlling the brightness with the potentiometer was a bit touchy, in that it could go from really really dim to really really bright with just a small nudge of the potentiometer (this guy shows it in his video: https://www.youtube.com/watch?v=CmWOdjyQGNM). This is to do with the human eye having a logarithmic response to brightness. You probably need to turn the potentiometer to about 50% before your eyes can sense a considerable change in the brightness which means that you're effectively wasting about 50% of the potentiometers range. I guess you could get around this by using a logarithmic potentiometer but I haven't seen that done before so I'm not sure how it would work in practice.

    There's loads more information about this out on the net, so if you're interested in reading a bit more about this I recommend some further google searching!

    Thanks a lot! It makes a lot more sense now! I think in my next project I am going to use your designs for the dimmer! :)