pigy back multi signal on one channel

Discussion in 'The Projects Forum' started by samjesse, Jan 20, 2011.

  1. samjesse

    Thread Starter Active Member

    Sep 14, 2008
    202
    0
    Hi
    I need help with a circuit I am making for work. I need to be able to view on one channel on the scope a multiple solenoid driver signal. They are activated sequentially. They are supplied with a common 12V and driven by separate drivers in a computer which grounds each at a given time.
    So the signal from one of the solenoids driver side would be 12v to ground and when the ground opened, it gives an inductive kick “hick” to say 80v. I want to view all the drivers signals on one scope channel.
    Many thanks
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    Can you simply "isolate" each signal with a diode, one for each solenoid, so that the signal going low on one solenoid does not affect the others?
     
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    80V sounds like a very big back-emf. It may be considerably stressing the driver device - are you sure this is OK?
     
  4. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    I just measured it. the BEMF is 40v and the amp is 3A.
    The reason I said 80v is to be more on the save side.

    The reason a diode on each sol. connection will not work is that when the 12v for one is pulled to ground, the others 12v will still show on the scope.
     
  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    you could use some triggered electronic switch with different DC level for each signal and place the 4 singals above each other. Don´t know what your frequency is, but probably you could do with just a one counter like 4017 and a 4060 switch. Of course the inputs have to be divided and clipped to fit the input range of the chips.
     
  6. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    The frequency is variable and not predictable.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Can you post your existing circuit without causing problems at your company?

    How fast does the sequence occur?

    You might simply connect an array of high-value resistors (say, 20K) to a common point as a voltage adder, but on the 1st relay in the sequence, use a 10k resistor (or two 20k's in parallel) to use as the trigger.
     
  8. samjesse

    Thread Starter Active Member

    Sep 14, 2008
    202
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    I do not have any circuts yet. the solenoids fire up as slow as 200 times per min. or as fast as 28000 times per min.
     
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