Trigger Delay

Discussion in 'General Electronics Chat' started by mehak, Jul 30, 2010.

  1. mehak

    Thread Starter New Member

    Jul 30, 2010
    I have connected sensor to 555 timer and that behaves like schmitt trigger but my problem is how i can find trigger delay?
  2. tom66

    Senior Member

    May 9, 2009
    Hate to take the obvious method, but have you tried a stopwatch or an oscilloscope?
  3. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    If it is too fast and you don't have an oscilloscope I would suggest long time constant RC filtering to get a DC level that you can turn into a duty cyle rating based on its comparison to the on voltage.

    If it is near 50% that will let you try the next step.

    Set up a known range variable frequency 555 timer that you think will include the frequency from your sensor and mix it with your sensor 555 signal. Again use the long time constant RC filter on the mixed output while you slowly vary the frequency on your variable oscillator. Either side of matching frequencies you will get beat frequencies that will cause the mixed outputs to pulse between 50% an max as if they were 100% duty cycles. This is the beat frequency as the frequencies move in and out of sync.

    Once you find the center frequency with your variable 555 oscillator you should be able to take a measurement of resistance where you had set the Potentiomenter to match frequencys and reverse calculate that frequency from the 555 frequency calculation formulas.

    Or you could set up a digital counter and tare it and stop it at a fixed intervals and calculate frequency in a PIC based on those sample counts.

    Or I would try using a multimeter with a frequency counting function.
  4. Wendy


    Mar 24, 2008
    Are you wanting to find out what it is, or to program a set delay in?
  5. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    If it is a single pulse then use it to turn on a constant current source and measure how much charge = Voltage that the constant current source will deliver into a capacitor of suitable size with one on pulse.

    Then you can reverse calculate the total charge/ constant current supply will equal your on time.

    You can measure femtoseconds with this method so it should be fine for calibrating your sensor pulse.