This should be an easy one...I think I am making it too hard.
I have a DC power pack that is used for model railroading. It outputs a variable voltage from -14 to 14 v DC. I am building some other digital control circuitry and I want to be able to detect whether there is any voltage coming out of the controller.
I have a LM339 that I was going to use but, that might be overkill. I am running my logic at +5 but, the LM339 has an open collector so, that shouldn't be a problem. And, it seems to have over voltage tolerance on the inputs up to 36V.
So, here are my concerns:
1. There is no discernible ground on the power pack output so, what are the consequences of making tying one of those leads to my circuit ground? I don't want to risk driving current into my digital circuits.
2. Can I have negative voltages on the inputs if I really only have a single supply +5V circuit? (i.e., I have looked at dual supply circuits but, I couldn't figure out how to accomplish it without having a second +/-36V power supply.
Maybe there is something even more simple that just uses a high-impedence transistor? (If so, I would have to make order and pay more for shipping than the chip).
Any help would be appreciated.
I have a DC power pack that is used for model railroading. It outputs a variable voltage from -14 to 14 v DC. I am building some other digital control circuitry and I want to be able to detect whether there is any voltage coming out of the controller.
I have a LM339 that I was going to use but, that might be overkill. I am running my logic at +5 but, the LM339 has an open collector so, that shouldn't be a problem. And, it seems to have over voltage tolerance on the inputs up to 36V.
So, here are my concerns:
1. There is no discernible ground on the power pack output so, what are the consequences of making tying one of those leads to my circuit ground? I don't want to risk driving current into my digital circuits.
2. Can I have negative voltages on the inputs if I really only have a single supply +5V circuit? (i.e., I have looked at dual supply circuits but, I couldn't figure out how to accomplish it without having a second +/-36V power supply.
Maybe there is something even more simple that just uses a high-impedence transistor? (If so, I would have to make order and pay more for shipping than the chip).
Any help would be appreciated.