555 Timer Photovore Robot

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This is a simple robot that I made for my cousin, it only uses 2 LDRs, 2 geared motors, and a 555 timer IC.

I reused a Tamiya Tank tread kit and gearbox for locomotion. All powered by 4 AA batteries. The batteries, IC, and switch are all housed in an Altoids tin.

Not much more to say about this robot (Sorry OddBot) 

Requested pictures: 

Schematic I found from the internet.

There's not much to see on the inside because i DeadBugged the 555 Timer.


EDIT: As of July 25, 2012 this robot no longer belongs to me. It has been shipped off to Chicago to give company to my cousin.

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I think Fly (great creature of God Allah) with ne555 not same or death Fly actualy not same

The original circuit with the LDRs will work fine on 2 conditions.

  1. you must use the TTL version of the 555 timer which can sink or source 200mA on pin 3. The CMOS version cannot drive motors.
  2. Your motors must draw less than 200mA.

Looking at your tracked robot I am certain that even if you are using the TTL version of the 555 timer your motors are trying to draw much more than 200mA! Treads haver a lot of friction and need a lot of current to drive them.

To get your robot moving you need to boost the current capabilities of the 555 timer. This circuit below will work with 1A motors.


Can BD139 be replaced with a 2n2222A and can BD140 be replaced using a 2n2907A?

I saw that you posted this on Shout Box.  OddBot answered this already.  Since you are still asking, let me try again.

Can you use the other transistors?  YES, —but...

As OddBot pointed out, if you use your transistors, you will NOT have 1 amp (or so) available to the motors. [1.5 amp max. peak for "Philips" brand]

I would put the current available using your transistors at maybe half an amp, and you should use these with heat sinks if you are pulling current towards the upper limits available through those transistors. Quoting Phillips, their 2N2222 is capable of 800 mA max, but their 2N2907 can only carry 600 mA.

 (Different companies turn out their own versions of 2N2222 & 2N2907 transistors and show different average and max currents and power dissipations for their individual versions, so go by the maximum available according to the brandname you are using. Do not assume they are all the same just because they were given the same number.  :-)

Other than that, yes, they may be substituted.


You can use other transistors but you must allow for the current draw of the motors. In the original circuit, because the 555 timer can only divert about 200mA of current, the robot turned in big circles. If your motors drew less than 200mA the robot would turn very sharply.

Adding transistors simply boost the maximum amount of current that can be diverted from a motor. Your transistor have a maximum rating of about 800mA. My transistors have a maximum rating of about 1.4A. In both cases they will get hot and the robot will turn in a much smaller circle.

You could put a resistor in series with the transistor to control how much current is being diverted and therefore how sharply the robot turns. Make sure to use 5W resistors of about 22Ω or less. It will take some experimentation to find what works best. A lot depends on the motors being used and the voltage of the battery.

D1 and D2 will be replaced with LDRs

Never heard of the term deadbugging before....and I've been doing this a long time.....

Is it soldering the components directly to the chip? I don't know,,,,



This usually refers to the way you look at a chip.




I guess I should have guessed that,doh! I do chips like that all the time, I just never had a description of the technique..

Thank, Maxhirez !