WOW~! Thanks to everyone for these answers, this is great. I graduated in Electronics many years ago, but really never worked in the field, just as a hobbiest.
Anyways, a couple of answers. The relay is a standard Bosch automotive relay. I can measure the coil tonight, but I'd imagine it to be pretty low.
I want to basically "trigger" this relay when the onboard car computer signal voltage jumps to 5V. That is the signal that tells the fuel pump to kick it up to a full 12V.
The voltage on the (-) side of the comparator just needs to be above 2.5 and below 5.0v. I originally was going to use a 3.5V regulator, but this is what I had. Are you saying that I could eliminate the regualtor, and just use the car's 12V supply through some resistors? If so, please help me figure those values, or draw what your saying 4.7KO in series to 1.8KO.
Also, what value Diode should I use for this "flyback" diode.
Also, are you saying that I could eliminate the NPN alltogether by upgrading the comparator?? I really like that Idea, less components, less costs. And yes, the NPN was inserted because of the higher current that the relay might need.
So in summary, I could possibly just use a larger capacity comparator for this and be done?
(PS what is a snubber?)
Thanks Again,
Stu
Sorry, the non-inverting symbol doesn't show up very well on your schematic. Your good there. What if you went with a different comparator, say an LM339 that can deliver more current? You could then eliminate the transistor and pull-up resistor on the output. You would have to swap your inputs and use the inverting side.