Zener Diode question

Discussion in 'General Electronics Chat' started by omega1974, Jun 18, 2014.

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  1. omega1974

    Thread Starter New Member

    Dec 3, 2012
    Hi All.
    I have an unusual request. I'm fitting a GPS Tracking device to a vehicle and as part of the installation I need to monitor when a switch (PTO) in the truck is activated. When the switch is off the output is +12v dc and when the switch is on the output is +24v dc.
    The digital input on the tracking device that I will use to monitor the switch goes to logic high when the voltage on it is in the range of 5v to 30v dc.
    My problem here is even when the switch in the truck is off, it at 12v, enough to trigger the digital input as high.

    I figure I need to use a zener diode so that only when the voltage passes through 18v up to 24v, it will switch on the digital input.

    The resistance of the digital input of the Tracking device is 15k ohms.

    Can anyone help with a simple circuit to solve my problem?

    Much appreciated.

    Best Regards,

  2. crutschow


    Mar 14, 2008
    Place a 15-16V zener diode in series with the switch output (cathode towards switch). Place a 10kΩ resistor from the zener output to ground. The junction of the zener and resistor is your output to the tracking device.
  3. Wendy


    Mar 24, 2008
    The owners of All About Circuits has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

    Please try to understand the reasons behind this action, and feel free to browse and use the forums.

    You might find answers to your questions in one of these forums:


    Another good forum that shares many of the same membership is http://www.electro-tech-online.com/ . Good luck.
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