My first robot..........

So I've decided to build my first robot which not the LMR "start here" one (that one is going to be my second one) and im using this circuit- . I've tried about 10 different designs for the body but its just not working. When i cover the left photocell with my hand and the other one is exposed to light the speed of the motors is the same and same with the right photocell. has anyone tried the circuit? did it work? or is it because the 555 timer can't handle motors that fast?( they are 11000 RPM at no load and 1.5 to 3V) Or is it because 1.5V is not enough for a 555 timer?

as the datasheet says: Min

as the datasheet says: Min 4.5V


after that there is no problem with this…



but still can’t understand how can a timer chip work as an MCU… :expressionless:


right :smiley: got the principle of this :smiley:


didn’t noticed the trigger-threshold connection :smiley:


as the upper LDR close the value of the treshhold will be closer to the ground (value 0) so the right motor having more current…

as the lower LDR close the value of the threshold will rise to 4.5V so the left motor will have more current :smiley:


I was rubbing my head that omg thats a timer where are the resistors for the signal :smiley: then I saw what and how it works :smiley: hm simple

ive tried using 9V but its

ive tried using 9V but its still not working. do you think its because the motors are too fast? i mean motors in most beginner robots are like 50 RPM and mine are like 11000 RPM. should i consider buying new slower motors?

Forget the speed of your motors

Motor speed is not the problem. However, you said that you have used 1.5v and 9v and it didn’t work. 1.5 and 9v are much less and much greater, respectivly, than the 4.5v required. Fix this. --Always start with what you know is wrong.

To be honest, that is about as far as I can go with an answer. If you can give a link to the post that goes with the schematic you have here, that would help a lot. Also, a clear picture of your robot showing all your connections and components would allow us to take a look and see if you connected anything wrong.

This could be a lot of stuff: Wrong voltage, motors too big for the 555 to handle, the LDR’s being the wrong values, the chip upside down, etc. etc.  --Get us that link and the clear picture of your set up and we will see what we can do.

heres the picture of the

heres the picture of the setup…

the motors are 1.5 to 3V.

the motors that i was using before these were 9-18V…

Pin 1 and 4

You have nothing going to pin 1 and 4 as shown in the schematic.

I’m not sure if the 2 LDRs are connected to both pin 2 and pin 6 or only pin 2 --Might want to try it both ways.


I just checked the specs. on the 555 and found it will only output 200mA. Your motors look kinda big --If they are drawing more than 200mA together, you may have fried your 555. Check the specs on your motors for current draw. Most of these little light seekers use very tiny motors (whatever the circuit) and no wheels. Because there is no gearing on your motors, most people simply allow the shafts of the motors to drag on the ground --the tiny diameter of the motor shafts becomes your “gearing”. I have also seen people use shrink tubing around the shafts for a little grip.

555 is definitely fried.

555 is definitely fried.