Voltage

Voltage
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Posted by: ericeb3 ^®

06/15/2006, 14:56:52

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I am useing a Pic 16f84a microcontroller to control a small 12volt dc motor. My problem is that the pic only runs on 5 volts. I have a 12v transformer power supply but with only 5 volts coming out of the microcontroller, and by the time it goes through a diode and my H-bridge I'm down to under 4 volts. When 4 volts is applied to the transistors on my H-bridge it only allows 4 volts to pass through the transistor to the motor. So how do I up my voltage comming out of the microcontroller so that I can have 12 volts for the motor. I have some relays but I would rather use trsnsistors for the H-bridge, and my relays take 5 volts anyway to run.

Thanks for any help

Eric

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Re: Voltage

Re: Voltage -- ericeb3 Post Reply Top of thread Forum

Posted by: randykimball ^®
Barney
06/15/2006, 18:42:38

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Are you looking for a varaible voltage or just to turn the motor on and off?
To just turn it on and off fire a solid state relay with the 16f84a output. Put a 1 meg ohm resistor across the input to kill any noise caused firing of the relay. Fire a standard relay with the out put of the solid state relay. The standard relay can be rated for the same voltage as your motor to keep it KISS, but should be rated for the current draw of the motor.
For variable motor speed you need to feed a motor speed controler rated for the voltage and current draw of the motor with the variable output of your 16f84a.
Use a separate power supply in the motor circuit for both applications.

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Re: Re: Voltage

Re: Re: Voltage -- randykimball Post Reply Top of thread Forum

Posted by: zekeman ^®

06/16/2006, 13:03:10

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What are you trying to do?
If you want to control direcion and speed in an H configuration, you could use the controller to drive the "bottom" transistors, substituting solid state relays for the top ones. Then you use a 12V drive across the H and allow the top relays to direct the motion while the controller modulates the appropriate "bottomn transistor. Make sure that the 5 Volt and 12 volt source have a common ground.

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