I need to detect the presence (with a TTL logic level output) of two separate power supply voltages, +7V and -7V. Is there a dual comparator IC I can use that will give me a TTL output for a negative/positive comparison?
What would the input circuit look like for this? Would a LM311 be a good choice? Would you pull up the output of the comparator to +5V?
The only thing I know about analog is: "Ground is where you grow Roses!"
The LM311 can be cranky and difficult to stabilize. I would suggest the LM393 Dual or the LM339 Quad. Make sure that any circuit you design observes the requirement that the input signals be within the common mode range of the device. You can satisfy the requirement by powering the comparators from +9V and -9V to measure values in the range [-7V .. +7V]
Thanks for the quick reply, I noticed in Ron's schematic that the power to the LM339 is single ended to +5V, am I reading that correctly, or do I need to power it with +/- 9V as "PapaBravo" suggests? Again, thanks for the circuit, I'll try it today.
Thanks for the quick reply, I noticed in Ron's schematic that the power to the LM339 is single ended to +5V, am I reading that correctly, or do I need to power it with +/- 9V as "PapaBravo" suggests? Again, thanks for the circuit, I'll try it today.
You are correct of course, I was not looking at it properly. I understand the circuit now, and I indeed need it only to detect the presense (or absense) of +/-7 volts.