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I am trying to design an analog direction driver circuit for an H-bridge configuration on a small DC motor. I have a pretty tight space constraint, and a simple requirement for my design, hence why I am trying to avoid microcontrollers. What I want to happen is for the motor to travel in one direction for 2.5 seconds, then to switch directions and travel for another 2.5 seconds. That's it for right now. In my design so far I have a 555 timer driving the timing side of things, and it is giving the desired output (HI for 2.5, OFF for 2.5 seconds). I also have the motor driver circuit built and functioning such that:

Input A = LO, Input B = HI - Output=Clockwise

Input A = HI, Input B = LO - Output=Counter-Clockwise

If In A = In B, Output = Stopped

My question is: How can I use the output of the 555 timer to drive the inputs of the H-bridge in the manner mentioned above? I am missing the link between the two sides of the circuit, and was wondering what suggestions you might have.

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You can use an inverter chip connected to your 555 timer output. That way you will get two signals, your normal 555 timer output and an inverted version. It sounds like you can use these two signals for your H-bridge.

555 timer output connected to H-bridge input A and inverter input, inverter output connected to H-bridge input B.

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    \$\begingroup\$ Wow, this just makes sense. Once I drew it out I realized how simple it would be. Thanks for your help, sometimes the simplest of things escape me! \$\endgroup\$ – CaffeineZombie Nov 13 '10 at 17:47
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    \$\begingroup\$ You can also use a single transistor and resistor pull-up as an inverter if a whole inverter chip is overkill. \$\endgroup\$ – W5VO Nov 16 '10 at 15:35

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