555 Timer Based Light Seeking Robot


Introduction: 555 Timer Based Light Seeking Robot

About: Just a tech enthusiast.

I have always been fascinated by robots especially one with the wheels because they are cheap, easy and fun to make and play around with. Recently I came across a circuit in one of the books. It was a light sensitive led circuit based on 555 timer ic. I modified the circuit just a little to make a cheap light seeking robot. Let's see how i did it.

Step 1: Materials

To build the bot you will need the below mentioned components.
1. 2x 555 timer ics
2. 4x 10k resistors
3. 2x LDRs (Light Dependent Resistors)
4. A breadboard if necessary
5. Some wires
6. 2x motors (with wheels)
7. 2x 0.01n capacitor
8. 9v portable power supply

And you may also need a messy workbench.

Step 2: The Schemetics

The schematic diagram of this robot is very simple to understand. As I had mentioned earlier I just modified a circuit from on of the books to create this one. Make sure that the motor you use DOES NOT draw a lot of current. 

Step 3: Chips on the Board!

Insert the ICs as shown in the figure. There will be a small notch or dot on every 555 timer ic. Make sure that the dots on both the chips should face upwards if you are going to build the robot as per the breadboard layout given in this instructables. Connect pins 8 and 4 together. Then connect pins 6 and 2 together.

Step 4: Power Source Layout

Connect pin1 to the negative rail on the breadboard. Connect pin8 to the positive rail on the breadboard. Do the same with the second chip.

Step 5: Resistors!

Now the most important part. Connect a 10k(brown, black and orange)resistor between the pins 8 and 6. Connect one more 10k resistor between the pins 7 and 6. Do the same with the next chip.

Step 6: Capacitors

Now connect a 0.01uf capacitor between the pins 1 and 5 of both the chips.

Step 7: Sensors

The sensors used in this robot are nothing but simple LDRs. LDR is a kind of resistor whose  resistance varies according to the intensity of the light falling on it. Connect the LDRs between pins 1 and 2 of both the chips. You can connect LDR either way as it does not have polarity.

Step 8: Conclusion

Now,  last but not the least. Connect your motor between pin3 of the chip and negative rail of your breaboard. Do the same with the second chip. Its all done! You have built a light seeking robot yourself! Connect a 9v battery and shine a torch over the LDRs. You will notice that the motors run! Place the motors in such a way that the LDR controlling it is in the opposite side. The LDR controlling the right motor must placed to the left

Step 9: Troubleshooting

If this project is your first electronics project then you may have some problems. Here are some tips to ensure that your robot works best.
1. Make sure that your connections are correct before applying power. (Use the schematic diagram because as this is my first instructables I was very excited and took the photos in a hurry and there might be some errors in the connection.)
2. Confirm whether your components are working properly before using them.
3. Use a low power consuming motor.


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57 Discussions

sir I want schematic diagram for making lfr using NE555.plzz help me.

2 replies

sir this robot follows which coloured line dark (black) or bright (white)

and how to adjust sensitivity of LDR

I am sure the answer to this is pretty simple since no one asked, but why is there a resistor instead of a capacitor? I have checked the astable mode circuit diagram and there is a C where the LDR is. I find that odd, shouldn't it be a Light Dependent Capacitor instead of a resistor (if such thing exists)?


2 years ago


1 reply

You can use some resistor in parallel with the LDR. Try experimenting.

i am a new starter at the robotics and i am really confused between which capacitor to buy because there are a lot of capacitors with different voltage values so plz can anyone send me a link of required the capacitors for this project on ebay.you can mail me the link on the below given id


Can you post a video of the robot in action? It would improve your I'ble and besides that, I' curious to see how it reacts to light... :-)

1 reply

Sorry! I have already used the parts in this robot to build others. I will try my best.

Hi, could u plz tell us how how did you get the values of the capacitors and why did you connect them in that why and plz show any calculations u did.

Thanks alot

3 replies

There was not much math involved in this build as I used an existing circuit with some very little modifications. It was a light activated led circuit where in place of led I attached the motors. The motors that I used needed very little power. If not then I would have added a transistor.

Sir i am using a 12V dc motor at 300 rpm. Problem is that there is not enough torque to push the robot. Can i use a transistor(til31c) to amplify the voltage

1 reply

Try using a lower power consuming motor. If you want to use a high power motor, check the datasheet of the transistor that you want before using it or simply use a motor driver.

SIR, thanks a lot. Will you please give me a working PCB layout for me ?? I have done it for my midterm project, and For final term, it is required to implement the robot with pcb. thanks :)

2 replies

I never designed a PCB for this robot. It will take some time. I will try my best and contact you soon.