using motors with basic stamp homework board

timeblade0

I recently purchased a basic stamp homework board from radioshack. I have completed the chapter in the book about servo motors. Now I am trying to get it to work with a small motor from a toy car that ran on 2AA batteries. I can get the motor to spin if I use vin + vss or vdd + vss. My problem is that I can't get motors to work from any of the pins. My code:

do
high 14
low 7
debug "working"
loop

I run wires from 14 and 7 to the motor, but it doesn't spin. I have used a multimeter and there is 5v in the wires. Any idea why the motor won't spin when connected to pins 14 and 7? I am new to this, so please explain thoroughly.

Mike Green

Motors typically require much more current than the Stamp can supply. You need to use a transistor to switch the motor on and off. If you want to be able to reverse the motor, you need an H-bridge. Do a web search for "wiki h-bridge" for a discussion of this. Parallax sells several h-bridge based motor controllers. The StampWorks kit includes an h-bridge. You can download the StampWorks manual and look at the exercises on this. There's a Nuts and Volts Column that discusses the use of switching transistors with a Stamp. You can find these columns by going to the main Parallax webpage, selecting the Resources tab, then the Nuts and Volts Columns item. The tutorial is under Resources, then Downloads, then Stamps in Class Downloads. You'll see a whole list of tutorials that you can download.

timeblade0

What does a transistor do? I have searched many places, but I still don't understand what a transistor does.
I looked at the h-bridge for motors. I understand how it can control a motor, but what controls the opening and closing of switches?

eWizardII

A transistor can control were electricity travels i.e. stop it or let it go, basically functioning as an electronic switch. Another role they play is they can amplify an electric signal. Hope that helps you in understanding their role in electronics.