Beginner Project

Discussion in 'The Projects Forum' started by Manmeet Singh, May 26, 2009.

  1. Manmeet Singh

    Thread Starter Active Member

    May 21, 2008
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    Hey guys I wanted to make an automatic feeder for an aquarium of mine ive got the logic down but not exactly sure how to implement it on the elctronics side of things. Idea is that I want to make a device that plugs into a power timer which turns on once a day, this will then activate a DC motor or servo (servos can rotate 360 degrees right?) so that a disc rotates a certain amount (not spinning) rotates a fixed distance and then stops and that is all until the next day. It sounds extremely simple compared to all these intense projects everyone has but gotta start somewhere! Im in second year computer engineering and have dealt with some electronics but application wise my experience is very limited!

    I have taken a course on microcontrollers but it mostely taught us about the nitty gritty aspects and we didnt really have to many labs that were to informative. So im thinking that I use some sort of programmable device (using a microcontroller would be overkill for something this simple right?) that checks the input at a certain port which is the AC power supply and once its gone high then it sends a PWM signal to the servo or motor to rotate the desired distance and then ends the program.

    Please advise
    Thanks!
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    1,305
    You could put a little switch (like a microswitch) and a bump/notch on the disk that operates the switch.

    When you get the voltage pulse from the timer, the disk starts to turn with a slow cheap DC gearmotor, and keeps turning by itself until the notch comes around once again and the switch goes open circuit again. I've seen exactly the same thing done in some electric toys, it should be reliable enough for a fish feeder?
     
  3. Manmeet Singh

    Thread Starter Active Member

    May 21, 2008
    37
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    Its more compicated then a fish feeder it has multiple compartments so the microswitch idea i doubt would work without adding alot more complexity. I think Ive realized more of the specifics of what I need for this project. So if Im driving a servo using a PWM signal and lets say the servo starts at position A and then i send a PWM signal and it moves to posotion B after I stop sending the PWM signal does the servo positioon reset to position A the neutral position? I need to know this in order to make my choice between using a servo or dc motor to have a fixed amount of rotation per day.
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    A stepper motor can rotate a specific number of degrees to a high degree of accuracy. This is probably simpler mechanically...but a bit more complex electrically...but worth it for the education. :)
    eric
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    If you are talking about a "RC servo" like used in model aeroplanes, then when you stop sending the PWM signal the servo goes into "low power" mode and just stays at the last position. However the motor can still freewheel due to not being powered, so it will hold the position only IF there is no load on the shaft.
     
  6. Manmeet Singh

    Thread Starter Active Member

    May 21, 2008
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    0
    Awesome I went ahead and did some research on these devices and it looks like they would be perfect for what I would need. However I have some questions on how the commands work.
    http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/sequence.html#single-coil

    The last example on that page with the half steps is exactly what I need for my project a motor that rotates 8 positions. So how do the commands actually work? Like would I send a 4 bit code to the motors driver to indicate which coils I want energized? Or since I have 200 steps until a full rotation would I need to issue 200/8 single step commands to get to the first desired spot of rotation?

    Thanks!
     
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