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Thread: Senior Project

  1. Senior Project

    My name is Jacob and I am a senior at DeVry University. I am just getting started on my senior project, I am building a robotic or R/C snow plow. I am using a taylor dunn stock chaser for the frame, drive motor, and the other electronics already on the cart. What I need to do is to setup a micro to control them rather than the manual foot pedal and switches. This is where I am struggling a bit. I am not sure how to design the circuitry around the micro to make it do this. O priginally forgot to mention that this is based around the atmega32.
    I need it to
    • control 4 24v inputs low current basically used as on/off for 3 relays and the main motor controller
    • control a variable voltage input 6-10.5v
    • pwm input to control a jaguar motor controller
    • other small various sensors that I am not to worried about yet
    The only thing I could think of was using a smaller set of relays to control the big ones.

    Any thoughts or concerns are greatly appreciated
    Last edited by modder man; 11-02-2011 at 10:12 PM.

  2. #2

    Re: Senior Project

    Depending on how much current the 24V inputs require you can use a transisor, solid state relays or regular relays powered via a transistor.

    The analog signal could be produced via PWM and a filter, it depends on how precise and fast the control needs to be.

    Assuming you have a datasheet for the motor controller or some kind of info the PWM should be easy.

    Never control a relay with another relay, thats sacrilege.

  3. Re: Senior Project

    That's what I figured, but I also didn't figure the micro could switch the 24v itself. I didn't know of any other way

  4. #4
    Join Date
    Jul 2008
    Rep Power

    Re: Senior Project

    A opto isolator circuit would work to control the relays.

    Just find one that fits your spec/needs and it should be available in a dip package as well.

  5. Re: Senior Project

    Ok update, the relay controller is built, I used an LTV-846 opto-islolater driving a fet to control the relays. THANKS for the advice

    I am now working on tackling the variable voltage input for my motor controller

    I need 6-10.5V at about 500mA current draw. I am a bit stumped on how to to this. I was looking at the possibility of using one of the PWM channels of the atmega to generate an analog output. I am not sure of what external hardware is needed to make this function though.

  6. #6

    Re: Senior Project

    What are you driving? Depending on how clean the voltage needs to be this could be a simple as an opto-isolater + fet attached to the pwm pin.

    Unfiltered PWM tends to do well with motors and the like but if you need a smooth voltage you might need to use an rc filter or some kind of complicated digital to analog + amplifier circuit.

  7. Re: Senior Project

    Its a golf cart motor controller, I would imagine it is not overly picky
    Last edited by modder man; 11-30-2011 at 01:41 PM.

  8. #8

    Re: Senior Project

    The 6-10.5V at 500mA is kinda a weird number because 500mA is a lot of current. That 500mA can't be directly driving the motor itself, but 500mA is way way more current than a control signal would require.

    It seems that most golf cart controllers use a pedal to control speed. Such an input should draw very little current.

    If you need to replicate a foot pedal your most "correct" option would be replacing the potentiometer (pedal) with a digital potentiometer that can be controlled from the micro-controller, possibly with an amplifier if the current draw is high.

    The easiest solution would be to replace the pedal with PWM going through an rc filter to smooth it out. You will need to poke around and see how much current the input actually draws though, anything much above 10mA will probably need a transistor since the micro-controller shouldn't source too much current and after a point the rc filter will be handling too much power to be practical.

    If you actually need 500mA you might be able to get away with only a transistor attached to the PWM pin. It looks like your easiest option for generating smooth voltage would be a digital potentiometer, lm317 and op-amp. Something like this: .

    Sending unfiltered PWM to the controller might or might not work depending on how it has been designed. I doubt any damage will be caused by trying though.

  9. Re: Senior Project

    my professor is sugesting I use an 0808 dac and an op amp, but he wont tell me how I should be hooking this up or which op amp to use. Do any of you have any input to that?

  10. #10

    Re: Senior Project

    I would probably start with a high current op-amp ( ) and do a basic amplifier circuit:

    Vin should be controlled by the dac.

    I don't know much about analog circuits but if you play around with a breadboard it shouldn't be too hard.

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