Hi all
I'm working on a design for a 12V power distribution board, my criteria being
There are plenty of "fuse blown" indicator circuits out there but I haven't seen any with a schmitt trigger like this, so as I haven't used one before I thought I'd run my design past you, dear reader. See attached - note led is red/green bipolar, ie current flows from A to B for green, B to Ground for red. I didn't have the right part in eagle.
The switch and relay are wired together as a multiway switch, and I don't see any issues here (standard 87/87A automotive relay). R2 and R3 are both 0.5W, SENS1 goes to a microcontroller and is high for "circuit on", and TRIG1 comes from a ULN2803A darlington controlled by the microcontoller and is high at 12V. D1 is to guard against power spikes by dumping anything above 15V to GND.
The theory is this:
My questions are - well, will it work I suppose, but more specifically can I use the 74HC14N to both source and sink current (20ma) like this, and do I need a diode between the fuse and the input to the trigger? I've seen a some similar circuits with this in, but I can't see why it's required.
Thank you for your consideration...
Cheers... Mike
I'm working on a design for a 12V power distribution board, my criteria being
- circuit can be switched on manually or via a relay, as in a multiway switch in a hallway.
- green LED on shows circuit is on, red LED shows fuse is blown.
- can set the relay from a microcontroller and read status of the circuit at the same.
- if the microcontroller or relay fails, I can still turn the switch on or off by hand.
- 24 circuits, so minimal parts and complexity.
There are plenty of "fuse blown" indicator circuits out there but I haven't seen any with a schmitt trigger like this, so as I haven't used one before I thought I'd run my design past you, dear reader. See attached - note led is red/green bipolar, ie current flows from A to B for green, B to Ground for red. I didn't have the right part in eagle.
The switch and relay are wired together as a multiway switch, and I don't see any issues here (standard 87/87A automotive relay). R2 and R3 are both 0.5W, SENS1 goes to a microcontroller and is high for "circuit on", and TRIG1 comes from a ULN2803A darlington controlled by the microcontoller and is high at 12V. D1 is to guard against power spikes by dumping anything above 15V to GND.
The theory is this:
- If the fuse is good and the circuit is live, the input to the trigger is high and output at point B is ground; the LED has current flowing from A to B so lights green, and SENS1 is 3.9V
- If the fuse is good and the circuit is open, the output of the trigger at B is low and point A is pulled low via R4. LED is off and SENS1 is 0V
- If the fuse is bad, the output of the trigger at B is high (5V) and A is pulled low via R4. LED is red and SENS1 is 0V.
My questions are - well, will it work I suppose, but more specifically can I use the 74HC14N to both source and sink current (20ma) like this, and do I need a diode between the fuse and the input to the trigger? I've seen a some similar circuits with this in, but I can't see why it's required.
Thank you for your consideration...
Cheers... Mike
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