Trigger/Gate Generation

Discussion in 'The Projects Forum' started by IceZero, Nov 21, 2011.

  1. IceZero

    Thread Starter New Member

    Nov 18, 2011
    Hi everyone,

    This is my first post on this forum and I was wondering if anyone would be willing to help me with a project I am currently working on.

    What the included schematic is "supposed" to do is to generate a gate of adjustable width once a trigger signal has been detected by the comparator.

    The input signal to be expect is a positive going signal with 100 nsec rise time, and 140 usec decay. The pulse amplitude will be around 400 mV and I plan to set the Vref around 100 mV.

    Would there be a problem with having the GATE output also controlling a transistor which turns on an LED as an indication? Or should I use the other unused monostable to generate the control signal for the LED?

    The other questions, is more of a request to have someone look over the schematic for me for some obvious errors.

  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    I don't see obvious errors.;)

    I would not leave the unused inputs of the SN74x open.
    Since the voltage you want the input signal compare to is very low you may consider using a resistor in series with the 5k potentiometer (pot to Gnd) This make better use of the potentiometer range.

    For the LED resistor you could use 270 to 330 Ohm which will give you a little less than 10mA.

    I don't see a problem in having the gate signal at the same output as the LED.
    IceZero likes this.
  3. IceZero

    Thread Starter New Member

    Nov 18, 2011
    Should I just ground the unused inputs then?

    Also I was thinking about the suggestion of adding an extra series resistor with the 5k Pot. I was thinking of just adding a fixed 5k resistor, which would allow the pot to adjust the lower range of the signal.

    Also, what would I need to change on the output in order to drive the signal through a 93 Ohm cable to a source which has an impedance > 1 kOhm

    Thanks for the help :)
    Last edited: Nov 21, 2011