Thoughts on indicator lights for a set of 12V fuses

RobotWorkshop

I am planning the main 12V power wiring for a rather large robot. There is going to be a fuse for each of the main drive wheels, on board computer, monitor, controllers (Propeller and others), etc. I'd like to add an indicator lights on each one of the fuses. I plan on using an LED and current limiting resistor to show the status of each fuse. There are two different approaches that I am considering. First, just use a GREEN LED tied to the load side of the fuse with the current limiting resistor to ground. With this all the GREEN LED's should light indicating a good fuse whenever the power is on. The other approach is to just install a RED LED with a current limiting resistor in parallel with the fuse. With this all the LED's should be off and if a fuse blows then there should be a RED LED on indicating the bad FUSE. If the circuit is toast it should act like a short and just pass a tiny amount of current 10-15ma at most to light the LED. I think that would look good since you'd only see an LED light if there is a problem. I'm just not sure how it would act if it was just a temporary overload that popped the fuse.

Has anyone done something similar when wiring up a project and what method did you choose?

Robert

kwinn

Generally I connect a green led on the load side of the fuse to indicate the fuse is good and the power is on. Convenient when you have several individually fused loads connected to a common power supply. You can tell at a glance if it is a power supply or load side problem.

erco

The "LED off unless the fuse is blown" option seems more useful. Your fuses go straight to B+, so why not route the load sides to a 339 comparator and let the reference voltage be a few volts under B+ (voltage divider). Comparator runs output LEDs directly. One 339 gives 4 comparators. You might need high-value pulldown resistors on your load sides, depending on what type of circuit is attached and what the failure mode might be.

RobotWorkshop

I do like the fuse lit when blown but I suppose there could be a scenario where something shorts out, blows the fuse, and ends up being an open as well. Then the LED won't lite. However, with the comparator as you mention that still work ok. I still have some time to think about it since I haven't started building the fuse panel yet. Just planning now and then gather the parts.

I think I have some 339 parts around and can try that out.

I'm still undecided. Green if ok or Red if bad.....

Robert

erco

How 'bout both? We robogeeks naturally love to see LEDs on. If you want to be tricky, get some 2-color LEDs that light green when the fuses are good, and red when they blow.

Now we're talking, Baby Boy!

RobotWorkshop

I'll try out each of the options on the protoboard to see what looks best. These are all hidden under a rear access panel normally they won't be seen unless the door is opened to check them or flip a couple of the switches. I just thought that adding the status LED's would be a nice touch to make it easy to spot problems.

And yes, I do enjoy seeing lots of LED's on robots for status and display. This one currently has 45+ of them. 20 on the body, 25 on the head and perhaps a few more scattered around. They originally had a simple 555 circuit w/cmos chip to sequence the lights but that is long gone. So, instead I am using a propeller and a bunch of tpic6c595 chips to control all the LED's. Instead of just cycling through them I can now display any pattern and fade them in and out. Should be a big improvement. The Propeller will also handle some of the other robot functions.

LED's rule.

Robert

erco

RobotWorkshop wrote: »

LED's rule.

Amen, brother! I drilled every hole to mount 400 LEDs in this little project that somehow ended up in my den:

http://www.youtube.com/watch?v=LvuZd0b9e_g