A very simple device. I've never really considered that LCDs have an accurate threshold voltage at which a segment will change state. I get the feeling this display has a higher voltage than average.
The use of printed resistors is an interesting evolution from the traditional surface mount ones. I suppose that a variation in carbon ink thickness isn't too critical as it still results in an equally scaled voltage divider.
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11 thoughts on “Inside an lcd voltage tester with schematic”
  1. Avataaar/Circle Created with python_avatars Peter Hughes says:

    I like that if the unit fails you could still use it as a screwdriver.

  2. Avataaar/Circle Created with python_avatars Shaun Stephens says:

    Merci mon ami.

  3. Avataaar/Circle Created with python_avatars Cats Meow Outside HBD says:

    I wouldn’t ever test anything greater than 12v with these things.

    I’ve been bitten before, once bitten twice shy

  4. Avataaar/Circle Created with python_avatars jp040759 says:

    WOW. Simple but complicated. Very cool idea. Sure are some smart/creative folks out there.

  5. Avataaar/Circle Created with python_avatars DjResR says:

    Stalwart brand from Maxima in Estonia has same device._

  6. Avataaar/Circle Created with python_avatars Pirelli says:

    You make good videos Clive and your warm voice is very pleasant!!

  7. Avataaar/Circle Created with python_avatars Jussi Kuusela says:

    I got laughed at in vocational school when I told people that everything that is conductive and has a surface area, including humans, has a capacitance, and that is how the neon screwdriver thingy (as well as this) is coupled to ground by the user to complete the circuit… and the reason why you will likely feel a small buzz in your fingers if you accidentally touch a live circuit, even if you are standing on a dry wooden floor wearing wellies and touching nothing else… and why if you touch the radio antenna the reception may be greatly improved in certain circumstances, and why touching the core of an audio input cable will cause a buzz on the speakers. Among other things. Likely many of them still think there's just some obscure magic to how these things work.

  8. Avataaar/Circle Created with python_avatars Tiago Ferreira says:

    That device is shockingly⚡basic! yet very clever design from the circuit point of view, but i wouldn't trust it for direct mains testing by any means.

  9. Avataaar/Circle Created with python_avatars carlu bambi says:

    Great device for killing its users .Never ever use a pen tester !Don't care what brand,Ideal Klein ,Fluke ,GB or Greenlee .Many an apprentice or journeyman have got themselves shocked or killed .Don't trust them in any way .

  10. Avataaar/Circle Created with python_avatars TheManLab7 says:

    Please DON'T buy one of these. Get yourself a multimeter which are around £10

  11. Avataaar/Circle Created with python_avatars TheRailroad99 says:

    Crazy how little components these are in this. 100% optimized to be economical

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