Question: I have DMM which is producing pulse with duration of around few microseconds. The pulse need to be sampled in PLC, which has sampling rate of 1ms. In other words the cycle loop can't be reduced to microsecond resolution. So it's impossible to reliably detect the pulse from DMM.

Could somebody recommend a simple TTL based circuit solution, which will be able to capture that microsecond resolution pulse and convert it into millisecond resolution pulse?

[![I](https://i.stack.imgur.com/orsZq.png)](https://i.stack.imgur.com/orsZq.png)

Answer: 
TTL solution with active low input and output. R and C are calculated for 2ms output pulse width.

![schematic](https://i.stack.imgur.com/BL5ef.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fBL5ef.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)
Instead of pulse extension, I suggest using a 1-bit counter (i.e., a toggle flip-flop, which you could make with a D flip flop and an inverter if you have to) that changes state every time it is clocked by a DMM pulse.

You can then use your PLC to detect when it's state is different from the previous sample.