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"Amplify" ground output?

Discussion in 'General Electronics Chat' started by Scruit, Jul 27, 2008.

  1. Scruit

    Scruit New Member

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    I have a home-made power controller that uses a "negative trigger" input (ie When the trigger input goes from +12v to ground the power controller turns on. The input has a pull-up resistor so that "open" is seen as +12v). I also have an off-the-shelf ultrasonic sensor that uses a negative trigger output (goes from Open to Ground when it senses motion).

    My problem is that the ultrasonic sensor either does not go fully to ground, or not long enough to reliably trigger the power controller. When I hook my multimeter to the ultrasonic sensor trigger output I can see that it the ouput does go towards ground, but it doesn't trigger the multimeter to beep in continuity mode.

    My question is: Is there an easy way to 'amplify' the ground output without having to make a new circuit? Would it make a difference if I changed to using a bigger or smaller pull-up resistor inside the power controller?


    There is a diode on the trigger input. Other negative-trigger devices work on the power controller input, and using a jumper wire to ground the input works also. Just seems that the negative trigger input (which uses a PNP transistor) needs to have the ground pulse be longer.
     
  2. saturn1bguy

    saturn1bguy New Member

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    What value pull-up are you using? You might be able to make it bigger (higher resistance) and thus make it less difficult for your triggering source to overcome.
     
    Last edited: Jul 27, 2008
  3. Mikebits

    Mikebits Well-Known Member

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    Do you have the spec sheet for your sensor, can you post it? Or a link.
     
  4. dave

    Dave New Member

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  5. Boncuk

    Boncuk New Member

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    use a pulse stretcher.
     
  6. Speakerguy

    Speakerguy Active Member

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    Ditto Boncuk. Lacking a scope to measure things with I would try a pulse stretcher to see if it's a timing thing.
     
  7. Mikebits

    Mikebits Well-Known Member

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    If the IOL of the sensor is weak, a zero level might not be achieved. In this case a pulse streacher will be of little use. Not to say that is not the problem, rather knowing the spec of the sensor would be the first thing I would want to check.
    I agree with Corey here, if he is using something like a 1K pullup, the sensor might not have the sinking needed to drive the line low.
     
  8. Speakerguy

    Speakerguy Active Member

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    If he uses a CMOS 555 as a pulse stretcher, wouldn't it take care of any timing and/or level and/or current issues?
     
  9. saturn1bguy

    saturn1bguy New Member

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    Well, certainly. But why add all that if peradventure he only has to increase the pull-up resistor?

    (It may not be a timing issue at all, really, if his triggering output is fighting an undersized pull-up, i.e. the smaller the pull-up the narrower the pulse will appear.)
     

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