Well, how about red when the fuse blows, and off when the fuse is good?
To do that, wire a resister, (1 to 10 Kohms depending on the led current
rating) to the side of the fuse that will be positive when the fuse blows.
Wire the resister to the led. Wire the other side of the led to the other
side of the fuse. Now, when the fuse is ok, there is almost no voltage
drop across the fuse, so the led is off. It the fuse blows, and its normal
load is connected, then the greatly reduced load current (1 to 12 milliamp
depending on the resister selected) will flow thru the led and light it up.
If you wire this circuit backward, you may destroy the led. To prevent that,
you can wire another led across that led but in the opposite direction.
Now, no matter how you wire it up, one led will be on, and the other will be
protected.
led
+-------->|---------+
| |
+---------|<--------+-------Resister-----+
| led |
| |
=========+===== FUSE =============================+========
OR
Battery ====+=====FUSE=============+===================Load===Ground
| |
+----->|-----Resister--+----->|-----Resister -----Ground
red green
led led
Green only, fuse ok
Red and Green, fuse bad
None, power off
Opinions expressed herein are my own and may not represent those of my employer.
Date: 19 Apr 1996 13:55:41 GMT
Original Subject: Re: HELP designing a simple switch circut!