Convert a Servo to Switch on and Off LED's




Introduction: Convert a Servo to Switch on and Off LED's

One of the most common parts in remote control electronics is the servo. They offer proportional movement using a potentiometer, gears, a motor and an H Bridge Circuit. What we will be doing is taking apart a tiny servo to remove the circuit and potentiometer. We will then de-solder the motor and solder wires in it's place. These wires will then go to LEDs to light them up.

One interesting part about LEDs is that they are diodes (Light emitting diodes) so electricity will only flow through them one way. Based on this principle when we attach them to where the motor was, when the motor would be spinning one way, the electricity flows one way and will light up the LED. When you flip a switch on your transmitter it would make the motor spin the other way which makes electricity flow the other way but it can't becasue the LED won't allow it through the other direction. This essentially turns off the light. When paired up (the + of one LED to the - of the other and vice versa) when the motor spins one way, one LED lights up, flip the switch and that one turns off and the other turns on. This is what we will be making

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Step 1: Take Apart the Servo

First you need to extract the necessary pieces. Remove the 2-4 screws to pull the bottom of the casing off, then pull the top off. Remove the gears as we will not need them. Then remove the potentiometer (It will have 3 pins and likely be what the main shaft of the servo rotates on. I had to cut my case to get it out without de-soldering the leads. You will then de-solder the motor and put it in your junk pile for some other project. 

Step 2: Prepare and Solder Your Interface Wires

I chose to put breadboarding leads on so I can experiment, however you can put on wires straight to the LEDs if you know your exact layout ahead of time. I cut the breadboard hookup wire in half so I was only killing 1 lead. Then I soldered each half on where the motor leads were. This will allow easy interfacing and prototyping. The Diagram below shows how the circuit works, note the position of the dial on the red servo tester. When centered (if the potentiometer is centered) neither light should come on. When turned one way, one color should turn on, when turned the other way the other color turns on. 

Step 3: Heat Shrink Time

You could easily use hot glue but it is harder to get back into the circuit if a wire comes out. I prefer heat shrink tubing. I put two layers around the circuit (so that when I put the potentiometer on it wouldn't poke through to the circuit). I then placed the potentiometer on top and slid a piece of heat shrink with a hole for the potentiometer shaft, shrinking each piece before putting on the next. 

Step 4: Done!

Now you have a remote controllable switch for lighting up LEDs, just plug it into your receiver. You will need to set up a switch and the process for doing this is different for every transmitter, follow your manual and figure it out. Also, you don't need to use a switch, you can use one of the sticks or you can do a mixing. One of the main reasons I thought up this design is so that I could mix it into the trainer switch. Then when I had control the craft would light up one color, then when I pressed the trainer button it will change the lights over and the trainee would know instantly when they had been given control. Give it a try and let me know what you think. 


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Showing it on auto (sweeping) with the servo to show what the commands going to the circuit look like.

This shows it plugged into a receiver and I am switching it on and off with the transmitter. 

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6 Discussions


Question 1 year ago

Dear @Ben The Builder,
Could you please help me, How to change led instead with relay 5v.
I mean that, using rc control relay.
Thanks and Best Regards

Ben The Builder
Ben The Builder

Answer 1 year ago

Hi @ReedN2,
I tried using this principle with a diode to drive a relay. The issue is that the power fed to the motor is pulsed, and at least with the servo I had the pulsing was slow enough that the relay would click on and off (something like 50 times a second I'd guess) which is really hard on the mechanical part of relays.

If you want to control a relay with a PWM signal (Same control signal used to drive a servo) Servocity sells an "RC Switch with Relay" that should work and it's currently only $10. It's a 10 amp relay. If you need more current than that, I'd still recommend you get the 10amp one and then just use that to drive the coil of a larger relay. They have a board that runs a higher current relay but it's like 6x the cost of the 10 amp one and thus more expensive than a 10amp relay and a larger one from an automotive parts store. Alternatively if you need a cleaner solution you might be able to de-solder the 10A relay it comes with and solder in a new one, but make sure the coil current isn't too high or you'll run the risk of burning out the component that drives the coil in the existing layout.

I know it's not as cool as making your own, but it'll probably work much better.


5 years ago on Introduction

If you add a gyro to the circuit after the servo driver and before the servo amp it will sense rotational motion


6 years ago on Introduction

Just curious how you ended up wiring your final project. How many total leds did you run? Wired in series or parallel? I am kicking around the idea of doing something similar on the 6v system on my 1/5 scale truck. I would like to run 12 5mm red leds in the rear and Y this into the throttle/brake servo to end up with functioning brake lights. I haven't actually purchased any leds yet, just tinkered around with some leds I have from previous projects, so I still need to figure up what specs I need on the leds. I would love to avoid having to run any resistors, which I am assuming with a 6v supply running 12 leds, I will have to wire in parallel and use at least one resistor. Will this end up draining my pack a lot sooner? (6v 4800mah)

I know I really need to start prototyping, but any advice you can give to start me in the right direction would be greatly appreciated.

Ben The Builder
Ben The Builder

Reply 6 years ago on Introduction

In the demo I did 9 total, it's 5 in parallel one way and 4 in parallel the other way. You will have to use resistors, try an LED resistor calculator, they're all over the web. I might also suggest that you try using a small brushed ESC (3-10amps) but the downside is running it with a Y you will have trouble getting everything to line up. You could very likely run 12 standard 5mm LEDs off of the H-Bridge from one servo and then by turning the potentiometer you adjust the point where the lights come on. As far as draining your pack, you won't even be able to tell with one that big, 12LEDs only draw a couple hundred miliamps so if all you had connected was the LEDs it would take 24 hours of full on to drain your pack