Science Buddies: "Ask an Expert"

Hello Mom of a 5th grader doing the "Light Tracking Robot" project.
Our Science Fair is Wednesday and this is a last ditch effort to save our project...

We have quadruple checked everything and...we can't get it to work.

Once we have the power source connected (batteries) and the switch is ON the motors run with light or without. The Potentiometer doesn't seem to make a difference.

We have searched the boards and found nothing.

PLEASE HELP before we label this science fair project a FAIL.

Thank you

Ps. Please find the photo attached

Hi - your photo is showing up as a broken link for me. Can you try attaching the photos again using the "attachments" feature below the main text box when you reply? If that still doesn't work you can email the photos to us at [email protected].

Bfinio: sorry about that!

I have tried again.

Thank you!

Hi - it's a little hard for me to see because that part of the breadboard is so crowded, but I think you have two jumper wires in the wrong place. The white jumper wire that's in hole J19 should move to row 18, and the blue jumper wire in hole J12 should move to row 11. The way you have it wired now, those jumper wires are in the same rows as the wires coming from the motors, connecting the motors directly to the ground (-) bus on the breadboard and effectively bypassing the transistor. This would explain why the motors are just always on instead of having the transistor act like a control valve that should control the motor speed based on the light level and potentiometer setting.

Another thing to watch out for - which again I can't see clearly in the picture - is to make sure that none of the exposed metal leads for long parts like the diodes and photoresistors are touching each other. Than can create a short circuit and prevent the robot from working properly.

I realize it may be too late if you don't see this post tonight or first thing tomorrow morning, but please let us know if you get it working!