Ready, Set, Go! Light




About: I like to build things... except for wiring.. wiring sucks.
This is a project I'm currently working on for my local combat robotics club. It is an LED light system that will signal the drivers when the match will start. Here are the goals I was aiming for:

- Physically appear similar to an older style traffic light that suspends in the middle of the intersection.
- Be controlled without a microprocessor (i.e. no Arduino)
- Internal power supply that can run the system for several days.
- Be protected from shrapnel and flying robots.
- Incorporate sounds as well as lights.
- Be very bright and look cool!

Testing at home:

A video of it in action (with brightness toned down):

Step 1: Circuit Design

Like I said earlier I wanted to accomplish the timing control without the use of a microprocessor. I'm using the 555 timer IC as it is simple to use and also very inexpensive as well.

The circuit is designed to have a momentary switch trigger the first light, and the next light is triggered when the first light shuts off. Repeat as necessary.

The schematic I've hacked together here (props to shows how I've wired the red and yellow portions of the circuit. You have to add an additional 555 timer 'section' for each light.

I used 100k resistors to get an approximate time of 1.1 seconds for each cycle. If you replace R1/R2 with a 1 megaohm pot you can easily vary the timing of your circuit.

A typical 555 timer can sink up to 200mA of current which is more than enough for a handful of LEDs. In my case I am using 36 LEDs per 555 timer which draw approximately 120mA.

Step 2: Building the Circuit.

To solder my circuit I picked up a proto board from the local electronic supply store. Cost me about $5 and I could probably fit about 3 of these circuits onto it. I cut out the chunk that I needed with a dremel.

I tested the PCB with some single LEDs and it works quite well. The measured the circuit drawing about 30mA as it 'idles' with no lights on.

Step 3: The Control Box

To house the circuit board, switches, and battery I picked up a plastic project box from the local electronic supply store for about $5 as well. The various parts you see inside:

The large red "start" button switch that is meant for arcade/pinball machines. Got it from the Electronic Goldmine.

11.1V 1000mAh Li-poly battery which I got from Hobby King.

15A toggle switch that will be the master power switch, got it from a local auto parts store.

5kohm pot that was supposed to act as a brightness adjustor. I included it as I had a few laying around but it ended up being pretty useless as the value was much too high.

12V beeper module from local electronic supply store.

Step 4: The LEDs

The LEDs I'm using are a little special. An older project of mine was building LED interior lights for my car. I'm using 5mm 'super flux' LEDs and even had custom PCBs made up for them. I special ordered some green and yellow LEDs for this project and soldered up all the light boards I needed.

Each board has 9 LEDs. (3 strands of 3 wired in series)

The run off 11-15V and have an input diode (reverse voltage protection) and 3 surface mount resistors.

Step 5: The LED Housing

To mount the LED boards I'm using a chunk of 2.5" aluminum tubing which is the same stuff I used in my RC Nerf Tank project. I drilled and tapped holes for 4-40 screws. The larger holes are for running the wires through.

Step 6: Protective Case

To keep the LEDs safe from damage I'm encasing them in a clear polycarbonate box. Some of it is 1/8" and some is 1/4" thick. Tapped and screwed together with countersunk screws.

Step 7: Assembly and Wiring and Trying It Out

I wired the LEDs to the control box temporarily, I will need to make a much longer cable when it is hooked up the arena. It seems to work well except I had to remove the beeper. I think perhaps it may draw too much current as the last 55 timer died when I first tried it out. I replaced it and disconnected the beeper and now it works quite well.



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    35 Discussions

    Robot Lover

    7 years ago on Introduction

    You could probably make a smaller circuit board if you use a 556 dual timer. :)


    8 years ago on Step 7



    8 years ago on Introduction

     What actually happened to the one robot in the video? It just span around and then died, but why!?

    1 reply

    Reply 8 years ago on Introduction

    It landed upside down and it wheels couldn't touch the ground. It looked like something broke off of it too so it might have lost power as well.


    9 years ago on Step 1

    you could also use a the 4017 IC (decade counter) and a NOT logic gate to supply the power to the 555
    (4017 pins
    light1 = output0
    light2 = output1
    reset on 4017 = output2
    not gate(in) = output2)
    (NOT gate chip
    the output of the not gate is to the power of the 555 and the input is connected to output2 on 4017(if using 2 lights))
    to output up to 8 lights then you only need 3 IC's


    9 years ago on Introduction

    I'm going to build a sprint starter light tree based on this idea. Any ideas how I can get it to work with four lights; 3 amber lights and a green "go" light? I need them to go on in 0.5 second intervals sequentially like this: 1 1+2 1+2+3 then stay on the green light #4 (or 1+2+3+4, doesn't matter) for at least a second or more. Any way how this can be accomplished? Thanks in advance for your help! Kevin.

    6 replies

    Reply 9 years ago on Introduction

    a 555 with a decade counter (each pulse from the 555 increments the light on the decade counter)

    Have output 1 light up 1 led through a diode
    have 2 output 1 and 2 led through another diode
    have output 4, 5, 6, 7, 8, 9 output to the 'green' led only, through a diode each.
    That follows the same idea, but uses a few transistors and runs a standard setup.


    Sure, add some basic logic to a four-timer cascade. I've attached a simple block diagram, however Instructables handles images. (Never done this before - adventure!) Anyway, T1-T4 are travis7s' timer circuits, the diodes provide the logic for T1 to turn on only light 1, T2 lights 1 & 2, etc. T4 only turns on the GO light. (I left out power & ground connections.) Keep in mind you may want to add a driver stage for the LEDs - you'll lose about .8V in each logic diode (using basic signal diodes like 1n914 or even 1n4001s), so your LED's won't be as bright. It may work fine as-is, but keep that in mind if you have trouble. You should also be able to find info to calculate resistor/capacitor values for your .5 & 1 second delays without too much trouble, I think it's on the 555 data sheet, which you can find online fairly easily.


    That looks good to me. You could account for the diode voltage drop by adjusting the LEDs current limiting resistor no? I had the time calc formula on my schematic. using a 10uF cap and a 47k resistor gets you pretty darn close to .5 seconds. Find one close to double or just put two 47k is series for 1 second.

    Ha, so busy with great ideas I didn't see the formula! And yes, the voltage drop could be helped by adjusting the LED resistor in this application. Hadn't thought that through completely. Other scenarios may present difficulties/oddities, though - Case 1: You end up with enough diodes to drop you below the forward voltage of the LED modules. Not likely with a 12V circuit, but could very well happen at 5V. Case 2: even with R adjustments, the way my logic is set up there could be either one or two diodes in there, which could make different lights run at slightly higher/lesser intensity. In this application I think that would look cool, but it might not be desirable. Also need to make sure the 555 has the power to drive all the LEDs/modules that need to be on at once. That's probably the bigger problem/reason to use a driver transistor, actually. Depends on the LED current draw.


    Reply 9 years ago on Introduction

    Hmm.. I'm not sure if there is a way to keep mulitple lights on. I'm really busy right now but after this weekend I'll see if I can figure something out.


    9 years ago on Step 1

    I like your idea.I know there is a circuit also doing the traffic light effect but which uses three transistors.


    9 years ago on Step 1

    The 555 is not a perfect source. Check out Thevenin's theorem for details; the actual source has a non-zero output impedance. In the simplest case, it acts as if it has a built-in resistance. Your selected current limiting resistor allows for plenty of source fluctuation. Good design there. In this case you don't have to worry about the output stage, but keep it in mind for future projects. If you really want to crank up the flash, consider adding an overdrive circuit (another 555 and transistor). Check out the data sheet for your LEDs, but you can pump a lot of juice into an LED for a very short amount of time without doing any damage...


    9 years ago on Step 1

    Just because the 555 can source 200 mA doesn't mean you should draw that much. The 555 wasn't designed as a stable current source, and LEDs need a stable source if you want to drive them safely and efficiently. How are you to choose a current-limiting resistor if you don't know the source voltage? Consider the case when one of the LEDs in your array dies. As the current put out by the 555 decreases, the output voltage will increase, sending more current to the other LEDs. This may lead to a cascade failure if you're driving the array near its limit. You don't need much more than a transistor and a couple resistors to make a suitable current source... why not put it in your design?

    1 reply

    Reply 9 years ago on Step 1

    I'm not sure I understand. I was under the impression the 555 outputs its input voltage, which is a fixed 11V battery. The current limiting resistors were selected for a source voltage of 15V (car alternator). Rest assured driving transistors was already supposed to be in the design, I just didn't have time for this version of the lights.


    Reply 9 years ago on Introduction

    The main reason is there had to be that mounting hole in that spot for the original project. No real benefit.