Since I am planning on using mostly fuses instead of circuit breakers, I thought it would be a good project to design an enunciator panel that would show the status of each fuse.
Initially, I was going to just wire a fuse and resistor to each of the outputs from the fuse box and have them poke through the panel. This would tell me which fuses had power, and which did not. Then, I figured I'd better put the LEDs all in one place, and maybe it would be good to put them on a perf board. Next thing, I was thinking "Enunciator Panel" and started thinking about all of the features that I wanted. I had some ideas about blinking LEDs when a fuse went out, being able to stop the blinking, having switches to disable an LED, etc.
This started getting complex, and I finally decided to just do a simple board that showed fuses with power as green and fuses without power out as red. Since I had some available, I started experimenting with a CMOS NAND gate and some LEDs. The NAND gate becomes an inverter if you tie both inputs together. I put an LED on the input and one on the output. With the right resistors, this seemed to do just what I wanted.
What I came up with was a very simple circuit that uses three CMOS hex inverters, one dual-color led per fuse input, and a resistor for each led. Three hex inverters gives you 18 outputs, which seemed about right. I can always install two boards if I need more. The CMOS is good because it operates from 2 to 15 volts, which is just right for our 12v electrical system.
I did a board layout in a few days, placed my standard 3-board order with ExpressPCB for $51, and had boards back within a week. At the same time I bought 20 Red/Green LEDs and 10 CMOS 4039 hex inverters from Mouser, which showed-up within two days. Everything went together without any problems, and this is the loaded board: