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555 Timer to control motor?

  1. Sep 19, 2007 #1
    I need help buiding a circuit that would use a potentiometer to control power from a small battery (AA's, 9 volt, or similar) to a small electric motor. I would like to have the motor pulse on for @5 seconds and then go off. The 5 seconds "on" would remain constant, but I would like the pot to control the off time, variable between @ 1 minute to 3 minutes. Any help or guidance would be greatly appreciated as this area is a little out of my scope of knowledge.
  2. jcsd
  3. Sep 19, 2007 #2


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  4. Sep 21, 2007 #3

    I'll try to just give a little input, I'm not an expert. And it depends on how complex of a design you want.

    If you're going to do timing with a digital chip, and you're controlling the timing with your pot, then you're most likely going to need an A/D to represent the voltage as a digital number. Then you will need some logic to tell what times each voltages correspond to before you put it into a timer. This would be really easy to do in something like a pic or low cost microcontroller rather than with logic gates (correct me if i'm wrong). Also, you will have to consider what voltage you're putting across the pot. I'm not sure if you would really want to pull it off the voltage supply to the motor, since this could cause transients and loading effects possibly from the motor. Its just something to consider when you go to the actual design.

    Another way would be to design a timing circuit with passive components like a simple RC circuit with its time constant, so you would have to charge and discharge for your timing. You most likely want to use buffers or opamps for this approach.

    Either way you might need a switching transistor or amplifier to cut off the power supply to the DC motor.

    I think the digital route would be easier and more precise, but I have little experience with simple designs. I've only controlled motors with PWM signals using an 8051 to control all the function and timing of the motor, and then a switching BJT and an H-bridge amp. So most of what you would be trying to do would be written in software in that design.

    Another thing to consider is what the motor is being used for. If its going to have a variable load, you might need a control system to apply the right amount of voltage rather than going full on/off with the battery.
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