Let's Make Robots!

Transistor based line follower

follows a black line on a white surface

Hi guys....



Finally today arrived the last order for this robot... the wheels and the caster....


I took me 2 night of CAD-ing...


This is  my first entry and I hope that you'll like this... I made this robot based on ermicro schematic and tutorial...  http://www.ermicro.com/blog/?p=1097


I used near the same things excepting the transistor... I'm using two 2N2222 transistor which allows 800mA on its collector... So the basic ideea is to follow a black line on a white surface... The principle of working is simple... I used a white LED to illuminate the surface... and one LDR as reciever/sensor.... when the white light contacts a white surface it will be reflected so the LDR lower his voltage opening the transistor... as the transistor is opening, the gearmotor gets more curent and will spin faster making it to turn...





unfortunatly I get tired with setting the trimpots every time when the illuminance changed... this way I was going to use QRD1114 fairchild sensor... and finally it's working... no more white light... :D just IR...


the only problem is that when my trimpots are at 0 Ohm, my LED isn't glowing :( the blue flashing LED :(

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could you provide a circuit Diagram/schematic using the 4 sensors?


just add two new qrd... the emitter hook up as i is here... the sensor should be hooked to a two new transistors... just the two transistor from the left should be hooked like base -> emitter on from another an the right one too... I'll do a simple schematic later...

I think A simple shcematic diagram would help alot. THANKS

only thing as I said... replace LED/LDR with QRD1114


a more complex robot could be made with KA339 or similar :D this is a quadruple comparator a double comparator could do the trick

ok right :D


here it is

Thanks alot! I really appreciate this. thanks for your time.

sure :) hope you will make something as cool as mine :) you need a low powered gear motor anyway :D and slow RPM

Regarding you 4 sensor schematics, did you create a robot with 4 sensors? I don't see how wiring the transistors like that would work. The voltage would always be the same. wouldn't it?

and what is the sensor alignment is it example A or Example B?


Example A



Example B




Was it versing robots with microcontrolers or not. If so that's very impressive!

After installing the Fairchild QRD11114 optical sensor, is it necissary to add the 2 10k variable resistors?