A diac in series with a cap, how does it work?

Discussion in 'General Electronics Chat' started by chunkmartinez, Jul 31, 2014.

  1. chunkmartinez

    Thread Starter Senior Member

    Jan 6, 2007
    I have been recently studying diacs(thyristors, triacs etc) because one(of the many projects) of the projects I am working on is a circuit breaker finder(a klein product I want to modify)You plug this small device in a 12v outlet and take another device and hover it over all the possible circuit breakers and a noise and beep triggers when you find it.

    Well I need help figuring out the simple outlet device which uses literally 2 components(not to mention a few resistors, led and diode for an led indicator).

    I checked the circuit and all it is, is a 470k film capacitor in series with a diac. That is all! I figured maybe the finder works by creating a certain current or current waveform and the finder detects it. I am not sure though and I am hoping someone can help me understand how the diac and cap in series works.

    My project here is to allow more then just 120v work(480v).

    So I have a 470k capacitor in series with diac k1200e07. Any ideas how this possibly works?
  2. MrAl

    Distinguished Member

    Jun 17, 2014

    I've seen and analyzed probably over a million circuits in my time, but there's always a new one. I'll take a guess at this one before looking more deeply...

    When the unit is plugged in the cap has zero volts across it making it a near short circuit. As the line voltage rises above the diac firing voltage, the diac resistance decreases suddenly and sharply. This sudden decrease causes a fast rising current wavefront that will be present in the entire circuit. A fast rising wavefront contains many harmonic frequencies of which some could radiate out from the wires in the house and even the breaker, and this would be in sync with the line frequency.
    The detector would have to be able to pick up either the RF energy that radiates out, or just the magnetic field. Once it detects this activity (which would be in sync with the line frequency) it turns on an indicator.
    If we could see the detector circuitry we could decide if it detects RF or the magnetic field.
    You could probably generate a similar signal in the line with a triac and control circuit which is known as a lamp dimmer, with the control set on some level like half dim, and a nice big 100 watt incandescent bulb.
  3. chunkmartinez

    Thread Starter Senior Member

    Jan 6, 2007
    Well according to specs the detector uses a micro controller which I'm a newb at but I will try and see what I can figure out.