Motor control without Hbridge

I've seen some commercial motor controllers on the net that use two transistors to control the direction of a DC motor. I'd like to build
this circuit myself and save some cost on the transistors. Does this require the use of a dual power supply? Anyone have schematics? I want to use as few I/o lines as possible. I am thinking 1 i/o line for On/OFF and 1 line for Forward/REVERSE.
R
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I have seen this done with a dual supply. One motor lead is connected to the middle of two batteries (for instance) one each transistor (or switch) from the other ends of the two batteries to the other end of the motor.
But if you want the least number of control lines, you should look at Locked AnitPhase configuration. (LAP does require an hbridge.) Takes one wire to stop, or go forwards, or go backwards, based on 50-50PWM, or 100-0PWM, or 0-100PWM respectively. http://www.geocities.com/robodave2000/circuits.htm
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On 31 Dec 2003 12:07:39 -0800, snipped-for-privacy@hotmail.com (Rich J.) wrote:

You can do this with two double pole single throw relays. Use the common line from the relays to attach to the motor leads. Connect the normally closed relay contacts to the the the + power supply. Connect the normally open relay contacts to the - power supply. When one relay is energized via an output line, the motor runs one way. When the other relay is energized via the other output line, the motor runs the other way. If no relays are energized, or both relays are energized, the motor does not run.
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On Thu, 01 Jan 2004 00:09:24 GMT, shb*NO*SPAM*@comporium.net (Si Ballenger) wrote:

Oops, I think that should be single pole, double throw relay.
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Rich J. wrote:

------------------------- Use a Totem-Pole with a dual +/- supply, that's the only way besides an H-Bridge. Model it after a TTL gate with a HI pulling, a LO pulling and an arbitrator transistor behind them to prevent both being on at once, and look at using an arrangement like a tristate totem-pole such as used with early TTL as well.
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Rich J. wrote:

You may want to rethink using an h-bridge. These units are real cheap about 65 cents.
http://www.fairchildsemi.com/pf/FA%2FFAN8200.html
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Or you could use 1 line by using an 8 pin microcontroller as a slave that handles the h bridge - it could have acceleration, deceleration, etc built in. The one line would just send control codes. The chip would cost a buck or two.
Mark

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