time delay relay alternative?

If the reset pin isn't asserted on 555, a signal below 1/3 Vcc on Trig sets the F/F and a signal greater than 2/3 Vcc on Thresh resets it.  It seems Trig dominates Thresh.  If this doesn't make sense, read about set/reset dominated flip-flops on google.  The combination of two comparators, a three-resistor string and a flip-flop is a very common occurrence in analog, the 555 is a great idea!  John is a great spirit and always accepts my chiding with good humor.  I try to twit him, but it never avails.

http://www.ti.com/lit/ds/symlink/lm111-n.pdf

The 311 comparator works up to 36V, if we use it, we won't need the VR, not that it a bad idea.  Look at example #50.  The output stage of the comparator is open-collector NPN.  So they are using it to drive a PNP output transistor, forming a http://en.wikipedia.org/wiki/Sziklai_pair.

The input stage works to slam the output stage based on the differential input - the offset voltage.  Gain is very high, but there is a small zone of metastability.  To repeat, if the + input is slightly higher than the - input the output slams high, if the - input is slightly higher than the + input it slams low.  Input range is a consideration with comparators.

We can make a string of a resistor (the 'ballast') and a backwards Zener and hook them across the supply to provide a reference, or we can just use a 2R string.  This would go to one input of our comparator, the other input would be attached to the tap of the timing RC across the supply.  When C charges past the threshold-we switch.  We might hook up a very large resistor (small conductor) from the output of the comparator to the + input (for example) to keep our circuit from chattering.  This is a form of a 'Schmidt trigger,' which removes the metastability.

If the reset pin isn't asserted on 555, a signal below 1/3 Vcc on Trig sets the F/F and a signal greater than 2/3 Vcc on Thresh resets it.  It seems Trig dominates Thresh.  If this doesn't make sense, read about set/reset dominated flip-flops on google.  The combination of two comparators, a three-resistor string and a flip-flop is a very common occurrence in analog, the 555 is a great idea!  John is a great spirit and always accepts my chiding with good humor.  I try to twit him, but it never avails.

http://www.ti.com/lit/ds/symlink/lm111-n.pdf

The 311 comparator works up to 36V, if we use it, we won't need the VR, not that it a bad idea.  Look at example #50.  The output stage of the comparator is open-collector NPN.  So they are using it to drive a PNP output transistor, forming a http://en.wikipedia.org/wiki/Sziklai_pair.

The input stage works to slam the output stage based on the differential input - the offset voltage.  Gain is very high, but there is a small zone of metastability.  To repeat, if the + input is slightly higher than the - input the output slams high, if the - input is slightly higher than the + input it slams low.  Input range is a consideration with comparators.

We can make a string of a resistor (the 'ballast') and a backwards Zener and hook them across the supply to provide a reference, or we can just use a 2R string.  This would go to one input of our comparator, the other input would be attached to the tap of the timing RC across the supply.  When C charges past the threshold-we switch.  We might hook up a very large resistor (small conductor) from the output of the comparator to the + input (for example) to keep our circuit from chattering.  This is a form of a 'Schmidt trigger,' which removes the metastability.