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.

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
-solder
-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.)

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

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.

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.  

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).

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).

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.

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.

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.

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.

Here are some more pictures of the finished bot.