[LM2917+JK flip-flop] = touch switch?

Discussion in 'General Electronics Chat' started by Tuppe, Oct 4, 2013.

  1. Tuppe

    Thread Starter New Member

    Dec 30, 2011
    Hello! I want to create a touch sensor plate switch using F/V converter method: http://www.pcbheaven.com/wikipages/How_a_Touch_Button_works/?p=1

    I tried to create constant frequency using 555 timer, and convert it to voltage, but I couldn't get it to work for some reason. Maybe the voltage had to be in the negative range and/or sine wave. Too bad I don't have oscilloscope.

    I saw a "Finger touch/Contact switch" circuit in the LM2917 datasheet, with JK flip-flop. Image attached of the circuit.

    What are those inputs coming for the JK flip-flop? J and K? Where do I connect remaining ¯CP, ¯R and ¯Q?
    What R values should I use? I don't understand the internal components at all, so I tried to guess some values with 3 potentiometers. After few minutes of fiddling I didn't get any resoults.

    I made the circuit assuming those 2 inputs are J and K and measured voltage, but I only get from 0-0.1v fom Q no matter what.

    Datasheed schematic attached.
    Last edited: Oct 4, 2013
  2. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    Here's a much simpler solution from Don Lancaster's CMOS Cookbook:

  3. Tuppe

    Thread Starter New Member

    Dec 30, 2011
    Thanks, I'll look onto that. Too bad that I ordered that JK flip flop and have to order antoher flip-flop ic again and wait another month for it to arrive...
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Be aware that CMOS circuits are damaged by static. Although the 4013 inputs have some limited inbuilt protection, the touch plate is wired directly to an input so you may zap the IC if you're wearing nylon knickers or trudging about on a synthetic-fibre carpet.