Let's Make Robots!

Trace - E

Follows lights

So after lots of hard-work, frustation, time, spending money on wrong parts; I built a robot. Its a Photovore based on NPN transistors. when its LDRs are pointed towards the floor, it becomes a line follower.

i used the following parts-

1.)  2 X 2N3904 NPN transistors

2.)  2 X Solarbotics GM9s

3.)  2 X Cds LDRs

3.)  2 X Wheels

4.) Battery holder

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Any updates on the diagram?? I am very itnerested on this kind of robots

Hi networkzombie,

Your circuit diagram need to be improved: Missing base resistors for the transistors, bases directly connected to 0V. I am wondering how the transistors shall drive the motors.

LDR = Light Dependant Resistor, so that takes care of the base resistors. I agree that the base of the transistors are probably not really connected to ground.

Hi ignoblegnome,

No. Please measure the resistance of a LDR under bright light. The resistance is nearly zero. This will damage the transistor. Two base resistors with around 2kΩ should be added and the transistors are safe --- even under bright sun light :)

Instead of connecting the bases with 0V (ground), two poti's can be added, then you can also adjust the sensitivity.


Nice robot,I like the transistors setups. Can you post the schematic please? Thanks and great job.

thanks! yes i will do that right now :)

i uploaded the video. And no i didnt forget the LMR logo. i will do that as sooon as i get a nice video editing software.

Thanks for the video. It looks like you have a very effective little light follower. Is the line tracing mode working as well?

I havent tried the line tracing mode yet although the motors do slow down when there's a black piece of paper in front of their LDRs and the speed remains the same when the piece of paper is white. I will try that as soon as i think of a modification :)



oh and a quick update - I added a power on indicator circuit.

Looks interesting....now lets see some vid of it moving!