Picture of Simple light seeking robot with 555 timing IC
In this Instructable I will show you how to make a robot that will be able to move towards a near by light source. This project uses a very simple circuit, so just about anyone can make it. I still have several improvements to make on this robot, but this is a good design for people who are new to this kind of thing. I made this robot using the 555 ic, because it is a very common, and easy to use component good for beginners, and does not require using programming or very complicated set up.
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Step 1: Materials and tools

Materials for the circuit:
-NE555N IC chip
-two identical photoresistors (often called light dependent resistors or LDR) (I had to order these from mouser electronics)
-two identical motors
-battery case for 4 AAA batteries (or AAs. depends on how much weight your motors can take)
-50k potentiometer
- printed circuit board
-bread board (for prototyping)

Materials for base:
-one piece of 1/8 inch plywood roughly 6" x 3"
-two other small pieces of scrap wood
-screws of various sizes.
-wheels (I used lego wheels)
-if you use lego wheels you will need a lego axle for two of the wheels.
-glue (gorilla glue is good if you have the patience otherwise hot glue will work.)

-soldering iron
-hot glue gun
-drill (and bits)
-screw driver

Step 2: Prototyping

Picture of prototyping
I guess this is technically an optional step, but I like to know something is going to work before I use it. this is where the bread board comes in. I will go into more detail on building the circuit in the next step.

Step 3: Building the circuit: installing the IC

Picture of Building the circuit: installing the IC
I bought an Experimenter Printed Circuit Board from radio shack. This is useful because it has the exact same connections as my bread board does. I also purchased the IC chip at radio shack. I will describe how to make the circuit in the captions.  

Step 4: Building the circuit: adding the Photoresistors

Picture of Building the circuit: adding the Photoresistors
When you buy the photoresistors, they will have long leads for mounting on circuit boards. You are going to need to solder longer wires on them so that they can extend out to detect the light. One resistor is going to be connected to ground and the other the power supply, but both are going to be connected to the thresh hold of the IC (pin 6).

Step 5: Building the circuit: installing the motors

Picture of Building the circuit: installing the motors
When buying motors, you want to make sure that they do not spin to terribly fast. try to get something between 3000 and 5000 rpm (if you get a motor that goes too fast, your robot will turn very slowly relative to its speed, so will not work) with more than 5.5g/cm of torque. You will also want to look for motors that have flat parts on the outside to make mounting a lot easier. Lastly make sure they have soldering tabs. Once you know that these motors work on the bread board, you may not want to solder them on to the P.C.B. right away. I drilled a hole in the base to put the wires through, and then soldered them. one motor will go to ground the other will go to the power supply, but both are connected to the output (pin 3 on the IC).

Step 6: Building the circuit: the switch, batteries and potentiometer

Picture of Building the circuit: the switch, batteries and potentiometer
To power your robot you are going to need a 6 volt power supply. You can use a battery case for either 4 AAs or 4 AAAs. while AAs last longer, the AAAs take up less space and are lighter. you will need a switch for obvious reasons, but be sure you use one that has no more than 3 leads on it. the pontentiometer is to keep the robot going straight when it is facing the light source, or to make sure other light sources or ambient light do not interfere. Try to get a 50k pot, but go you can go higher if you think you will need to.

Step 7: Building the base: mounting

Picture of Building the base: mounting
Cut off the part of the circuit board that is not being used. take the small piece of ply wood, and plan out where you are going to put everything. You do not have to make it the way I did, but it seems to work well. drill two holes near where your motors are going to go. feed the wires for the motors through this these holes, and attach them to the circuit. Draw a line about two inches from the back end of your bard, that is perpendicular to the sides of the board. line up the two motors on this line and glue them down. screw in a piece of scrap wood above the motors, and attach your battery case here. Put the circuit board on the other side of the wood than the battery case is on. glue the potentiometer and switch to the front of the board.

Step 8: Building the base: the wheels

Picture of Building the base: the wheels
What I have found in building this robot, is that almost every problem you have can be traced back to the wheels, so you need to be very careful to line up every thing perfectly, and that no wheel has more traction or anything. Although I did not do this, I strongly recommend that you use gears on the wheels. I had some lego wheels laying around, so I decided I would use them. Use bigger wheels in the back than the front, but try to make the front wheels sit lower than the back wheels so the whole base is angled up. keep the front wheels very close together, and not too far from the back wheels (this improves handling). for the front wheels attach them to a lego axle, and then screw that onto a small piece of scrap wood. screw the would onto the base tightly using only one screw so that you can adjust it.

Step 9: Using your robot: trouble shooting

Picture of Using your robot: trouble shooting
Once you attach the wheels, your robot is complete, but it may not seem to work at first. This is not because you did something wrong, but more likely because you need to makes some adjustments. If your robot seems to only turn in one direction check to make sure that both of the back wheels have the same amount of contact with the ground, and make sure that your front wheels are perfectly straight. If your robot turns in the opposite direction that it is supposed to, switch around the direction the LDRs face. If one motor seems to be more sensitive to the light, adjust the potentiometer. Every time you use your robot you are going to have to play around with the positioning of the LDRs, and the potentiometer until it starts working, so don't give up if it does not work right away. Take it from me, it is very rewarding once you get this robot to work.

Step 10: The End

Picture of The End
Here are some more pictures of the finished bot.
swiftquail29 days ago

you can make a simple one with 2 555 timers, 2 photo resistor ,and 2 stepper motors

AQibM10 months ago


kirankd AQibM1 month ago

did u get the circuit diagram of the project

Higgs Boson (author)  AQibM9 months ago

It's the last picture on step three, I think.

kirankd1 month ago

can u send the circuit diagram of this project

jEnNrhANz057 months ago
do somone have the circuit of the project??
jEnNrhANz057 months ago
I dont understand tge shem... plz do someone has a good quality drawing?? plz I really want to make this Project.. thankz
it is not working . when the light is off then it should not work but is working with out light also then what is perpose
Higgs Boson (author)  theshivakumar0433 years ago
Yes this is true. in the dark the robot still runs. this may seem to defeat the purpose of having a light seeking robot, however the robot is designed to seek a state of equilibrium with the light. in other words it moves until the amount of light on both LDRs is the same. That being said, in the dark with identical amounts of light on the sensors it will move straight. My suggestion to you if you don't want it to run in the dark, is to add two NPN transistors to the motors so that no power will go to them unless the light exceeds a certain level. I am going to experiment with this circuit a little bit, but if it works I will be sure to post it.

how to add two npn transistors at motors.. show the schema please? and what kind of the NPN transistors that can use, what type of it?

annekristania9 months ago

hi Higgs Boson!

this robot always be running nonstop,although a little light or a lot of light.

What should i do, to make this robot stop at brightless and it running when there are some bright lights?? please help me for my school project.. please give me that modified schema, thanks before :)

avenged7x1 year ago

Can I use a 9V battery for the robot, or is it strictly 6V?

schel1 year ago

UGH! I really REALLY wanna build this but, from the drawing (because the photos aint helpin') It looks as though power+ is going into the 555 on pin 8 AND at the end of pin 4 (reset) which is connected to a motor.....is that correct? the same thing at an end of the LDRs with a 2nd ground running from it...in addition to pin 1 having a ground from/to power...correct? Great, idea, superb on the simplicity of the parts but, sure frustrating with out clear instructions..ie step by step and/or useful circuit images. Thanks for postin' tho!

Higgs Boson (author)  schel1 year ago

Yes. That's right.

It would be good to see your contraption in action. Any possibility Boson?
Higgs Boson (author)  terrible tinkerer2 years ago
Regretfully it is no longer in one piece.
chelle.cee2 years ago
Hello im interested with your project but i'd like to know specifically what type/kind of identical motors that your pertaining to? Because i need the specs. your reply will help a lot and will be highly appreciated Thanks ! :)
Higgs Boson (author)  chelle.cee2 years ago
Unfortunately I no longer have the exact specs on the motors, but they aren't very critical. As long as the motors that you use have identical specs so that one doesn't pull harder than the other, etc. A problem that I ran into was that the motors I used spun too fast and didn't have much torque. I fixed the problem by using a Tamiya gear box.
pboylan2 years ago
It's difficult to see what's above the ic when you are installing the motors, could you post a clearer picture of that?
Higgs Boson (author)  pboylan2 years ago
I would...but alas this robot is no longer in my possession. Looking at the schematic should tell you everything you need to know though.
rishi19933 years ago
how much voltage motor should i buy for this project that is?
Higgs Boson (author)  rishi19933 years ago
1.5-3v. The 6v power supply should divide the voltage well between them, but look for a slower rpm, or the motors will turn so fast that the change in speeds which is supposed to make it turn will have no affect, not to mention the issue with torque.
rishi19933 years ago
how much voltage motor is used
i have used 1.5 v motor it run very fast freely but when i put it on ground it does not run .please help me
Higgs Boson (author)  rishi19933 years ago
The motors just do not have enough torque. You could look for a slower motor, but I recommend buying a tamiya gear box. they are only about $10 off of amazon and should solve your problem, giving your motors a lot more torque.
Derek Vigil3 years ago
A good idea would be to use a solar panel so that way it could charge itself.
Higgs Boson (author)  Derek Vigil3 years ago
If you did this then you would need to get a solar panel that can produce 6v.
Or four mini solar panels that produce 1.5v each.
Higgs Boson (author)  Derek Vigil3 years ago
Yeah that would be cool. it would find the light to charge its batteries, and then keep going. Just like a living organism looking for food.
great idea, it seems like living technology is not far off.
Mwahahahahaha! I am making that.
avi553 years ago
Could you tell me how to modify the circuit so that the robot out to a source of infrared light instead of a normal light?

Higgs Boson (author)  avi553 years ago
If you replaced the LDRs with phototransistors and put a visible light filter over them that should work, maybe even just putting a visible light filter over the LDRs so that more or less only IR light can get to it.
SUBYRIDA253 years ago
So I'm trying to build this robot and I'm kind of unsure as to what specific parts I should buy.

For the motors: Radio Shack sells motors that run about the speed you describe. (a little faster actually) but they say they are 1.5-3 volts. Can I use them because the voltage is split between two motors or will the 4 AAA batteries making 6V be too much for them.

Also, can you send a link for the specific photoresistors you used in this project? Thanks for the help.
Higgs Boson (author)  SUBYRIDA253 years ago
The radio shack motors should work. (I think that is where I got my motors) but you should try to find slower, or even get a gear box. If you choose to use a gear box, I recommend using the tamiya twin motor and gear box which you can get on amazon for about $9 plus shipping. You could use any photoresistor, photo cell, cds cell and so on for this, and unless I'm mistaken I'm pretty sure radio shack sells some photo cells that would work fine for this. either way here is the link address from where I got my sensors:

if copying pasting the address doesn't work tell me and I will include a link in the instructable.

P. S. the 1.5-3v motors should work fine.
Ok, Thanks, I went to Radio Shack and picked up the parts. I am using a chip that read 555p and not 555cn. The package said 555cn but the chip is different i'm guessing. I thought maybe it was a manufacturer difference. Do you think it will still work?
Higgs Boson (author)  SUBYRIDA253 years ago
So long as it has 555 on it it will work.
charlez953 years ago
Modified circuit.jpg
how can i increase a motor's torque
Higgs Boson (author)  spankeerrrrrrr3 years ago
you could add gears, but usually you just need to buy it with more torque.
i also want a drawn circuit in jpeg format
he wont. he is a very secretive guy (or gal???)
so please post it
He is not going to post it.
Higgs Boson (author)  Master anuroop3 years ago
I don't understand how doing it in ms paint will make it any better
cambigfoot3 years ago
Really??? for the past week ive been trying to find a light seeking robot circuit and i finally found one 2 days ago XD
R.A.T.M3 years ago
agambhir3 years ago
is awsome but please give me a photo of a drawing of circuit drawn in ms paint
Kiteman3 years ago
How bright does a light need to be for the robot to follow it?

For instance, in that last step, it seems to be following reflected torch-light.
Higgs Boson (author)  Kiteman3 years ago
It is not so much the brightness as the angle it strikes the LDR. Although it does need to overpower any ambient light, or other light sources in the area. Otherwise anything should work.
tycoon123 years ago
Higgs Boson (author)  tycoon123 years ago
Did you read through it?
Higgs Boson (author) 3 years ago
I have a hand drawn schematic, but I based the schematic off of something else I saw on instructables.
Do you have a full schematic? Even hand-drawn is fine.