Here is a paper that I found on the subject of demodulating the time signal from the WWV broadcast by the U.S.. I am also doing some experimentation with using the WWV as a time source to synchronize a couple of devices.
http://www.eecis.udel.edu/~mills/database/reports/wwv/wwva.pdf
Here is what I would like to do.
1. create a system that will project an image onto a normal pair of sunglasses or regular glasses.
2. information will be transmitted from a normal RCA output.
3. must be small enough to conceal (don't want to look like a cyborg).
4. Image must be transparent do...
Lewish is absolutely correct that is about the cheapest that can be done. You say you are using a LM7805 but you only want to be alerted after the voltage goes below 6V, to error on the side of caution when using regulators (LM7805) if should be 2V above regulated voltage I suggest a 7V warning...
The only way I can see to solve this problem without redoing the entire circuit would be to put in place a relay system that trips when you have the negative voltage input. Sorry if this of little help to you.
you could always build an IR relay and place it in a window that did have LOS with the object and then use your scope and remote to control it then very easy to do with a IR sensor, a 2N2222, a 2N3904, a couple of resistors, and another IR LED.
Try a PT6302 this will take a 12v input and produces a fairly stable 5V output ripple is only like 20mV(p-p) if I remember correctly. It has a 3A output max. It is made by Power Trends I use them alot. I get everything from 5V-9V out of these chips with a few mods. It comes with its' own...