I have created a robotic gripper. However, I need help in the control circuit:

Control schematic

There are two buttons, the upper and lower one (connected to the timer):

  • the upper one is two states timer either up or down (will be replaced with an active low pin in PCB design).

  • the lower one is a push button that must be pushed and let back to its initial position to give a pulse to the monostable timer to make the servo rotate long enough to just close the gripper (calculate with the RC circuit).

My problem: I want to replace the down button with some component so as to give a quick pulse when the upper button change state.

For example, the button was 0 and went 1 -> Component -> a small pulse to drive the timer (not a pulse that will last until the state changes):

Timing diagram


  • Green: is button state
  • Red: trigger pulse needed.

1 Answer 1


This can be easily done with a 555 timer, or even a flip flop and a counter. Are you looking for design concepts or a detailed design?


Check out this site for a simple edge-triggered one-shot that uses two nor gates and an R-C (scroll down to the NOR Gate Monostable section). I can't draw the circuit on here using my phone so I apologize about just providing a link.

  • $\begingroup$ Detailed if possible. $\endgroup$ Jun 22, 2017 at 2:04
  • $\begingroup$ Thanks, actually I totally forgot about edge triggering. I am gonna use this sub.allaboutcircuits.com/images/04190.png I hope it can be simulated on proteus. $\endgroup$ Jun 22, 2017 at 10:38
  • $\begingroup$ How to implement both negative and positive edge triggering in the same circuit $\endgroup$ Jun 22, 2017 at 10:53
  • $\begingroup$ Use a NOT gate and replicate your one-shot. $\endgroup$
    – SteveO
    Jun 23, 2017 at 4:09
  • $\begingroup$ Thanks so much SteveO for your help. Wish you all the good luck. $\endgroup$ Jul 3, 2017 at 22:13

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