Photocell circuit help

[Burgerz]

I am trying to build a small robot that will turn left and right depending on which side you shine a flash light on (think of a photovor) and I am having problems with the photocells I am using. In my circuit I am hooking up a NPN transistor to ground, and a photocell (photo resistor) to the NPN transistor's base, so when the photocell receives more light, enough voltage will be able to go through and ground out the circuit. By doing this, I am hoping that the motor that is hooked up in a parallel path will stop, as the energy will take the path through the NPN transistor as it is the easiest path to the ground. My problem that occurs is that when I hook up everything in this way, the Photocell uses up large and irregular amounts of voltage, causing there to be not enough voltage to trigger the NPN transistor. For example, on a 3v circuit it will use up a total of 2.3 volts, and .7 v will flow out, and on a 6v circuit it will use up 5.4 volts and .6 volts will flow out (this is all under the same light conditions). Moreover, if I try to make a series circuit in which the photocell is placed before the motor, the photocell will use up almost all 6 v, and barely any voltage will flow out. What am I doing wrong in this circuit and how can I fix it?

 

[Grossel]

Do some testing first

Hi.

First of all I'll tell you what I would do in your place:

• I would have run an easy test to the photo cells to ensure I was able to make them trip a bjt properly.
• Then I vould have done yet a simple test on the circuit. I would placed variable resitors in place of the photo cells to ensure the circuit actually behaved as expected.

Further on I would shared schematics with the guys on the forum. You might just have assembled it wrong, but can't tell unless you show us the schematic.

Ps: If upload, please don't use word files (ending with doc, dot, dotx or docx) as current version of Libreoffice doesn't reproduces ms office graphics properly.