Converting a 10v FSD meter to 5v FSD?

Discussion in 'General Electronics Chat' started by Lotus-e-Clan, Dec 31, 2014.

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  1. Lotus-e-Clan

    Thread Starter New Member

    Dec 31, 2014
    I'm a classic car enthusiast but not a purist so have done a few electronic upgrades over the years to my 1973 Clan Crusader track day car.

    I want to use an old 52mm analog Autometer Air Fuel Ratio (AFR) gauge to work with my Techedge WBO2 ECU's analogue linear AFR output. The problem is that FSD for the Autometer AFR gauge requires 10v and the ECU outputs ONLY 5v FSD. So how can I make the 10v analogue guage read FSD with only 5v max from the ECU?

    The autometer gauge has a three wires: black (GND), red (12v) and violet (10v AFR signal). I connected the ECU 5v output to the violet signal wire and 5v max gave just 1/2 FSD as one would expect! I measured the resistance between GND and the violet signal wire on the Autometer AFR gauge and it reads 158.4 k ohms.

    I guess I need to wire a resistance in parallel across the gauge signal input but I'm not over confident about doing this! I was thinking about using a 100k resistor + a serial 100k potentiometer together (200k total) then wiring these in parallel with the gauge so I could turn down the pot to dial-in about 160 K to get the 5v output to show FSD ... is this the right way to do it?

    The Techedge ECU already has an accurate digital serial readout for AFR so I can check the analogue result against the digital output - the analogue gauge is easier read than the digital output btw, so that's why I want to use it.

    Any help -suggestions appreciated!

    thanks in anticipation.

    Peter Knibbs
  2. wmodavis

    Well-Known Member

    Oct 23, 2010
    An opamp with gain of 2
  3. Lotus-e-Clan

    Thread Starter New Member

    Dec 31, 2014
    Thanks for prompt reply! :)

    I should have said that I'm a biomedical educationalist by profession with only a little 'self-taught' electronics experience, so whilst I've met an op amp before in the dim distant past, I only have fuzzy recall of its (many IIRC) application(s). Do you have any particular OP AMP circuit design in mind that I could try/copy? :D
  4. 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 . Good luck.
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