I used to have a machine where an action could be triggered on a pontential free contact with a simple micro switch (that worked pretty easy and well for me). That machine got replaced and the new machine needs a TTL input as trigger signal. Unfortunately for me the TTL interface of that machine is almost not documented (all I know is the pin assignment).

Now I am a bit lost how to achieve that. As far as I understood I need to pull that TTL input to something between 2V and 5V right? Now I guess that I cannot just use that micro switch to connect some 5V power source to that TTL input. I'm also concerned about the switch bouncing and triggering multiple signals on the new machine (the old machine didn't accept any new signals until the previous action was completed so bouncing wasn't an issue as actions took >1 second).

So my idea was to use some Arduino to handle the micro switch signal (maybe debounce it if needed) and pull that TTL input to 5V for some defined time to trigger the machine.
Would that work, or is that a way too complicated and can be achieved much easier?

Would it work with a simple 5V power source and the micro switch between the TTL input of the machine (if it doesn't need debouncing).

I'm a bit stuck here and I'm prett much a noob in electronics but not afraid using a soldering iron if that's going to solve my problem.

  • \$\begingroup\$ Testing to create a TTL pulse <=0.8 to <=2V is pretty easy. Then define the function if it is edge triggered or level to sustain function or something else? \$\endgroup\$ Aug 16, 2021 at 15:02

1 Answer 1


This is very simple. You'll need a 74LS00, a DPST switch, and two resistors. The circuit looks like


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Thx for your response, I think I get the logic idea with those 2 nands, but I have 3 more questions: For application reasons the switch needs actually to be a pushbutton not a switch (sorry my bad) does that work too? • What 5V source could I use (I'm afraid of giving the TTL to much mA)? • Does this pull high as long as the switch is closed or just one pulse? • Sorry for asking those noob questions, but some explanations would really help me. \$\endgroup\$
    – Pᴇʜ
    Aug 16, 2021 at 15:27
  • \$\begingroup\$ @Pᴇʜ - 1, It will not not work with a simple, 2-contact switch. However, it is possible to get DPST pushbuttons. 2, Use the same 5 V as you provided the Arduino. 3, It pulls high as long as the switch is pushed, then cleanly releases when you stop pushing. No fixed-width pulse. \$\endgroup\$ Aug 16, 2021 at 16:04

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