Fuse block LED’s

alright here are a few diagrams that will work...

The first 3 all do the same thing in a different way. first one uses a relay, and a resistor, 2nd one uses some reistors and a diode, third uses some resistors and a transistor.

The next 2 diagrams are to shut it all off when the car is not running. This is only needed is the fuse has power when the car is off, if it doesnt have power when the car is off this is not needed. First one uses a transistor, second uses a good old automotive relay.

Also the circuits all derive power from the unfused side of the fuse, i only did this to make the diagrams much easier to read, but would recommend, that the lead that is attached to the unfused side actuallt be connected to a fused power source of its own.

The reason i drew 3 different diagrams is just to allow you to choose the one you want, I would reccoment the first one if you are only going to hook this up to one or two fuses and want the ability to use a dual color common cathode LED.

The second one i would recommend if you are using it for 1 or more, but do not plan on using a dual color LED.

The third i would recommend for 2 or more, a dual color LED can be used with this set up. I only say 2 or more because it uses a transistor, most people dont have transistors laying around (just about any PNP transistor will do). This setup uses much less current than the relay diagram and slightly less than the 2nd diagram.

The second last circuit (the relay used to shut this off), I would recommend this for any number of fuses because of the current this wll aloow.

The last circuit (same purpose as previous) i would use only for less than 10 fuses. although the resistor value can be changed to allow about 20 to be used.

Let me know if you guys use these or want more info.

ohh if you want to use a switch just use it to apply ground to any of the first 3 circuits.

Dont be afraid of the circuits, to some they may look complicated but they are really not, if you have any questions just let me know.

hah thanks wvsquirrel,

For 10 fuses i would definitly go with the third one, you want to hook it up so that the fuse in the diagram(looks like a sine wave labeled F1 or F2) is wired so that the right side is the ouput of the fuse, the side that has no power when the fuse is removed. The reason it has power from the other side also is so that the red can illuminate when the fuse is actually blown.

Yes you would have to use the circuit for each fuse, its really not as difficult as it looks, i could probably make the circuit for all 10 on a 2" x 2" board, you defintly want to use some perf-board or a circuit board or it will become a big mess, lol

haha cat-5, i use that stuff all the time for things, cat-5 would work just fine, although you only get 8 wires, but that no big deal.

Parts for fig. 3 diagram:

Q1 - 2N3906, PNP general purpose transistor (last time i saw these at radio shack they were in a package of 15 i think for like $2) very common transistor.

R3, R4 - 4.7 K Ohm resistor, Just get 1/4 watt, 5% or 10% tolerance, doent really matter that much, i think radio shack sells these in packages of 5 for like $0.50

R5 - 560 Ohm, same 1/4 W...

LED - well the circuit is designed for a 2V drop 20 mA LED, i would reccomend a dual color common cathode RED / green LED, just because it will look cooler. I have no idea if radio shack would sell these...?

I would also get a piece of perfboard, with the copper doughnuts, if you can solder.

Oh i thought of the second diagram, then as i was drawing it thought of the 3rd, then the first, then the last 2 haha, i actually had another too, but it ended up being too many parts to make it useful.

Let me know how it goes.

for the perf-board, if you think a different kind will make it easier go for it, im used to the stuff wit just the donuts.

If they dont have 560 i would go for 620 or 680 first, if they dont have that then go for 470, or you could get twice as many of 300 Ohms and put 2 in series for 600 ohms...

Dual color LEDs (RED / green) are very common you shouldnt have much trouble getting some.

resistors dont have polarity so just put then in anyway you want.

No thank you, nobody ever builds these circuits I draw up, im just glad someone is, maybe ill jam the parts in some perfboard and take a picture for you if you want, the way i think it would be easiest to do, it doesnt really matter though.

I assume you will but i would build just one and try it out to make sure it all works correctly before making them all, you can just touch the fuse wire to 12V to see if the LED changes...

Good Luck, ohh do they still sell the 2N3906 transistor in like packs of 15?

wel if thats all they have go with the 470. the transistor has to go in a special way,like so:

if you look at the transistor notice the one side is flat and the other is rounded, the view above would be looking directly down on the circuit from above, I also labeled the emitter, base, and collector (the three terminals of the transistor).

If you want the pin layout in a 3-D view check out the datasheet for the transistor: https://www.fairchildsemi.com/ds/2N/2N3906.pdf

here is the layout i did, its less helpful thta i thought it would be, i didnt solder anything.

Although if its the first time you build something on a board i would recommend not trying to jam everything in a small area, space it out a little and color code wires, i used blue for ground, red for constant power, and green for the fuse terminal.

Let me know how it goes, good luck.

Wow, first person to build a circuit i drew up hah.Yea take a picture when you are done i would love to see it. Other ideas, i have plenty what else do you have in mind? I have a small circuit here that will use a momentary switch to toggle a relay on and off and change LED from red to green and back and such, nice for fog lights and other things that usually require a toggle switch, thats one i remember because i just built it, a little more complicated than this but nothing you can't handle

I think most people are turned off when they see the diagrams, it wasn't that hard was it?