Need support to create a detecting sircuit

Hi all, it have been to many years since i played with the real stuff, cant remember much to save my life so i depend on you :-)

Need help to create a signal detecting circuit. Detect Signal 5V 1ms pulse but dont trigger on diagnostic 100mv 1ms pulse. Need to measure over 2.2ohm existing resistor without disturbing measured circuit to much. When detecting signal, turn on diode and keep it on until retested by user button.

by Joshen74
May 04, 2019

You can use Schmitt trigger to make it work. When detect signal is higher than triggering voltage, Schmitt trigger turns on the diode. You can reset the circuit by connecting input of Schmitt trigger to 0V. You can put a diode between input of Schmitt trigger and the 100mV signal to block any feedback from Schmitt trigger.

by wangwg88
May 04, 2019

Added some information. I dont have a common ground as R1 is in a black box. Can a Schmitt trigger be used in that case?

by Joshen74
May 05, 2019

in your schematic, bottom pin of R1 is common ground.

by wangwg88
May 05, 2019

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