Hello,

I've got an old motor that I salvaged from a busted CD-ROM drive. If I hook up the battery one way, it spins forward. If I reverse the battery, it spins the other way.

I figured that I could use 4 transistors to flip the direction of the current but I was wondering is there a simpler way?

Thanks,

mj

 

You could use a DPDT (double-pole, double-throw) switch, like this:

You'd be best served to get a switch that has a center-off position. Suddenly reversing a motor by flipping it's polarity is very hard on it.

 

I forgot one additional detail

I plan on buying a gumstix computer on module that I want controlling this thing. Aren't DPDT switches flipped by hand?

Thanks,

mj

 

Yep - so much for that idea.

You'll need an H-bridge then - or a couple of SPDT relays (which will suck up power).

Have a look at this web page: http://www.solarbotics.net/library/circuits/driver_4varHbridge.html

 

You could use these they are motor H drives from old VCRs very easy to use & cost nothing if you salvage them from old machines. Daryl

 

I forgot about the L2722 power opamp for a bit; they can be used as well.
Datasheet: http://www.st.com/stonline/books/pdf/docs/1321.pdf

Look at Figure 8, on page 5. These power opamps are under $1 at many distributors. Digikey carries them.

 

Thanks!

Two questions though.

Why are the resistors necessary as inputs into the transistors?

Also, what are those symbols at the top that look like a stylized "S"?

mj

 

Thanks!

Two questions though.

You're referring to the schematic on this page: http://www.solarbotics.net/library/circuits/driver_4varHbridge.html

Why are the resistors necessary as inputs into the transistors?

Did you read the text?
Current to the base of a transistor almost always has to be limited via some means when the transistor is used as a saturated switch.
Without the resistors, it won't work at all.

Also, what are those symbols at the top that look like a stylized "S"?

Those are symbols representing hysteresis, or a Schmitt trigger. A 74HC14 is a hex Schmitt-trigger inverter.