Velleman VM188 or MK188

Discussion in 'The Projects Forum' started by Leckyneil, Oct 19, 2014.

  1. Leckyneil

    Thread Starter New Member

    Sep 25, 2013
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    Does anyone know if it would be possible to substitute the jumper for a switch for the start with 'pulse' or 'pause' on a Velleman VM188 (or MK188), without it causing harm to the circuitry?
     
  2. KMoffett

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    Dec 19, 2007
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  3. Leckyneil

    Thread Starter New Member

    Sep 25, 2013
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    Thank you Ken, I will give it a try.
    The problem at the moment is that the VM-188 is not consistent with it's timings, probably because it is not crystal controlled. I don't suppose there is a solution for that.
     
  4. KMoffett

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    Dec 19, 2007
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    What amount of "not constant with it's timings" are we talking about ?

    Ken
     
  5. Leckyneil

    Thread Starter New Member

    Sep 25, 2013
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    That was quick!!
    I am just going to test timings with my Android app, will get back to you soon.
     
  6. Leckyneil

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    Sep 25, 2013
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    I discovered that for the first ten (approx.) pulse/pause cycles it was wildly inaccurate, sometimes adding as much as ten seconds to the time, but after that it was spot on with the timings. Am I right in thinking that this is due to temperature?
     
  7. KMoffett

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    Dec 19, 2007
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    Is that the first ~10 cycles after power-up, then timing is correct? If so that's not too uncommon for R/C oscillators.

    Ken
     
    Last edited: Oct 27, 2014
  8. djsfantasi

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    Apr 11, 2010
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    So is it possible to take ten timings, discard the result and then use it for timing thereafter? Sometimes, the equipment needs to warm up. I've seen it with PIR sensors.
     
  9. KMoffett

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    Dec 19, 2007
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    I guess we're down to what are you trying to time.
    Sometimes it'd easier for us to help solve you problem, than help solve your solution! ;)

    Ken
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
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    a crystal costs about ten cents, while this Velleman circuit for sure costs at least $10.
     
  11. Leckyneil

    Thread Starter New Member

    Sep 25, 2013
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    My project is an automatic tracking camera dolly. The VM188 controls the voltage to a Celestron NexStar SLT Telescope Mount which is pre-programmed (using Camera Wizard) to pan endlessly between two positions. The first position uses the pulse low voltage for slow speed pan (6.23v), and the second uses the pause high voltage for high speed pan (11.3v). I have a voltage regulator to ensure it never goes over 12v.
    The dolly travels along a track endlessly using a motor, relay, micro switches and 3D printer timing belt.
    You will notice that none of this setup has a common sync, and is open to a lot of variables, but I'm vainly hoping that I can get some sort of synchronicity.
    My original question is for when the dolly changes direction along the track so that the VM starts in the opposite mode to what it has been doing.
    I hope this makes sense, please let me know if you need more info.
     
  12. KMoffett

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    Dec 19, 2007
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    I have no idea what Camera Wizard is or how it works. How do you see theVM188 controlling the voltages?

    Ken
     
  13. Leckyneil

    Thread Starter New Member

    Sep 25, 2013
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    Sorry Ken for not explaining better.
    Camera Wizard is a function on the NexStar hand control for setting the pan/tilt positions (or GoTo positions when used as a telescope mount).
    In addition to the voltage regulator I have a variable controlled power supply with LED display. When the VM is in pulse this is in circuit providing the 6.23v, and when the VM is in pause it is out of circuit providing the 11.3v. These voltages can be seen on the LED display.
    I will send a photo of the setup soon.
     
  14. Leckyneil

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    Sep 25, 2013
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  15. Leckyneil

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    Sep 25, 2013
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    Here are 4 photos of the rig.
    In yesterday's description I said 'The dolly travels along a track endlessly', what I meant was 'The dolly travels forwards and backwards along a track endlessly'.
    I have managed to get it to run for 5 cycles before going out of sync. It then takes 2 cycles to catch up on itself, but of course it is then going in reverse ie. the slow pan has become the fast pan.
     
  16. KMoffett

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    Dec 19, 2007
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    Losses sync with what? And I still have no idea what the "slow speed pan (6.23v), and the second uses the pause high voltage for high speed pan (11.3v)".
    You are assuming that we know what and how this whole assemblage does.

    Ken
     
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