dc motor encoder output signals (or lack of)

Discussion in 'The Projects Forum' started by kutalinelucas, Aug 17, 2011.

  1. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    Hey guys, I'm looking for a little advice...

    I have a faulhaber (micromo) 1624 s motor with built-in magnetic encoder. I've been trying to hook it up to my propeller chip but I'm having difficulty getting any results. The thing is, when all is wired up and the motor is spinning ( very slowly ) the voltage across the encoder outputs remains at a stable 1.6v...but I'm assuming this should be fluxuating. I don't have a scope, just a multimeter but at ~1.5 revs/sec and considering theres only 12 pulses per revolution I'm guessing there should be some activity.

    On the data sheet there is a schmatic of the output circuit for the encoder ...

    [​IMG]
    but theres somebody on another forum who's convinced it isn't nessesary and has used these encoders without the circuit

    So i'm here to ask those in the know if...without the circuit in the attached image, would the encoder lines show no dynamic output? I have no problem ordering the bits, but if there should be some activity on the encoder outputs without said circuit then something else must be wrong...

    Thanks for looking
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I can't find anything on the manufacturer's website about a 1624 s with an encoder attached. The only option is shows is for a DC tachogenerator. are you sure it doesn't have a DC tach on it? The image you posted I can't find in the literature; can you post a link to where you found that? I am accustomed to seeing that particular circuit inside of encoders. It's called an NPN open collector output. I don't think you need to construct it.

    when reading with your meter, you would see 18 pulses per second. that may be too fast for your meter to register. try turning it by hand and stopping at several positions until you find a position where the voltage goes to zero. Also, if its pulsing at 1.6V, that may be below the threshold of what your propeller chip recognizes as a digital input. I dont know anything about propeller.
     
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
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    on second look at your pic, the way they drew those lines dashed on the left makes me reconsider. maybe you do need to construct that circuit. I won't know until I see more data
     
  4. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    The data sheet was pretty tricky to track down...took me at least half a day but i've attached the document.

    I am almost certain its a hall effect quad encoder..I'm new to the concept of dc-motors, but it just makes sence that there would be a noticable change of voltage as the encoders pass. My multimeter is nothing fancy, but it will easily pick up a < 5mS pulse coming out of any mp, and i've held the scope across it for some time hoping to see some response, but not even a flicker...

    I don't mind if I need to order the bits, but it would be nice to know...since i'll have to wait a few days for delivery that it'll sort the problem.

    Thanks for your help

    Martyn.
     
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
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    do you have 3 & 4 tied together as the picture seems to show? if so, that could be the problem. what voltage are you putting into pin 2?
     
  6. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    well no...at the moment the two encoder outputs go directly into 2 consecutive ports of the propeller on the recomendation of somebody who has apparantly used this method effectively.

    If I did have transistors in my house, i'd put the transistor and resistor between the ground and vss on each output.
     
  7. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Good, that's how it should be.

    I really don't think that'll help. If the voltage going into the base of the transistors isn't changing then I doubt that the voltage coming from the collector will change.
    Can you verify that the ground (pin5) of the encoder is connected to the ground of your propeller and that the VCC (pin2) has at least 4.5V on it?
     
    kutalinelucas likes this.
  8. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    its sorted!!! thankyou so much...I had connected ground on the ground rail right next to the prop, but I have a Electrolytic cap between vcc & vdd on that side...not sure how that would effect grounding the encoder but I just plugged it directly into the prop ground and it sprung to life!

    thanks for the help...you've probably saved me days worth of head scratching...
     
  9. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    hate to be cheeky but could I just ask one not totally unrelated question...?

    I have a number of both steppers and Dc motors within close proximity...DC circuit theory isn't really my strong point so do you think noise may be an issue? and could this effect the operation of either the motors or encoders?
     
  10. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I wouldn't anticipate it being a big deal. you can always just hook it up and see. if you're talking about for a permanent installation, you can mitigate the problem by running the encoder signals through shielded cables.
     
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