I have two Sensors S1 and S2, S1 is a 24v inductive proximity sensor which i isolated using octocoupler to work at 5v and S2 is a transmissive type phototransistor sensor, both are placed at a fixed distance , signal from S1 will is always triggered periodically and used for reference but if the product is defective S2 will not be triggered.
I have to catch if S2 does'nt trigger within 0.9 seconds S1 is triggered.
My initial idea is to use XOR but there is a time difference delay i.e S1 and S2 might not be simultanious. How should i acheive this without a microcontroller.
Instead of XOR if i use a 555 timer with the required time interval and trigger the pin 2 of 555 with S1 and use S2 to retrigger to keep 555 output always high and when S2 fails will the output from pin 3 goes low? but i think retrigger from S2 will be considered same as debounce of S1
S1 ____| |________________| |_____________
S2 _________| |___________________________
Error ___________________________| |____
Figure 1 by @Transistor for OP to edit.