I need to make a circuit even when the push button pushed and released very fast, the final output will stay ON at 12V for roughly a second. %10 accuracy for the timing is fine. An LED will indicate the ON and OFF time. I tried to combine couple of circuits to obtain the goal.
Below circuit uses C1 and R4 for adjusting the pulse ON time. LM2903 is used as a comparator. The output of the comparator is buffered by a transistor buffer to obtain enough current to the load and the LED. The need for buffer is to obtain better results for different loads:
And here is the voltage and current waveforms from the simulation for the nodes marked as n, p, op, out, LED current I(D1) and switch current I(S1):
My problem in this circuit I cannot add hysteresis. Because if I add positive feedback it will be connected to the RC timing circuit. I might overcome this by changing R4 but I cannot even create hysteresis by adding a resistor between the nodes out and p.
How can I add some hysteresis to this comparator without affecting the function of this circuit? Is there anything fundamentally wrong or missing with this design?