ABS sensor tester circuit

Discussion in 'The Projects Forum' started by IJKR16, Jan 24, 2016.

  1. IJKR16

    Thread Starter New Member

    Jan 24, 2016
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    So I've been given this circuit (attached) that needs to be built due to urgent need and I'm the only maintenance guy here with enough (although not much) knowledge to throw it together. My main problem is that I don't have access to the zener diode and I only have a 9v battery attachment. I have all the other components, as well as some 1N4148 diodes (75v/10ma). Is it possible to lower the resistance to compensate for the 9v battery and somehow use the regular diodes to achieve the same effect as the zener diode? Also, I'm pretty sure they made a typo on the LED and it can actually be 5v or whatever. Anyway, I just have to throw something together that will do a good enough job until I can get the actual parts online. I appreciate any help.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    The zener is dropping 5.1v the led probably is a 2v forward drop, so thats 7V across the switch the resistors total 570 ohms dropping 5V thats approx 9mA led current,
     
  3. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    That circuit really doesn't make any sense; It appears to use a 12V LED in series with a 5V1 zener fed from a 12V supply and, thererfore, it will never illuminate. Why put a 470Ω and a 100Ω resistor in series and not just use a "near-enough" 560Ω?
     
  4. IJKR16

    Thread Starter New Member

    Jan 24, 2016
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    Yeah, that's why I'm thinking the LED is a typo. As far as I know they LED just needs to illuminate, nothing special. For the resistors, I think they just used what they had on hand.

    Anyway, aside from the voltage drop, would there be any reason they used a zener diode instead of a regular diode? And would my diodes even be usable here since they are 75v/10A?

    **Also, I guess I should have mentioned, somebody who has no idea about circuits just forwarded this to me to figure out and they got it from somebody else who had it forwarded to them, etc. So as much as I wish I could just ask, I'm kind of stuck here. As long as the circuit behaves the same, I can design it however I want.
     
  5. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    The zener diode really does nothing in this circuit, it is even shown fitted the wrong way round so it will behave just like a normal diode. You need to know the spec of the ABS sensor, it's impossible to deduce anything from this worthless circuit.
     
  6. IJKR16

    Thread Starter New Member

    Jan 24, 2016
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    Alright, I'll see if I can dig anything up. Thanks for the input.
     
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