1
\$\begingroup\$

I want to detect with a microcontroller if a fuse has blown. The circuit with the fuse is 12V when on (it is not always on, so I need to distinguish between a blown fuse and the circuit not running). The microcontroller can only handle max. 3.3V.

I thought about using two optocouplers like this: enter image description here

Is there a better solution you would use?

\$\endgroup\$
  • \$\begingroup\$ Nvm. I presume 3.3V- is essentially the ground (0V) for the MCU? And that 12V- is the ground for the +12V supply? \$\endgroup\$ – Tom Carpenter May 23 '18 at 23:07
  • \$\begingroup\$ Yes. Sorry, could've used a better syntax for that \$\endgroup\$ – Henry May 23 '18 at 23:10
  • 1
    \$\begingroup\$ measure the voltage across the fuse \$\endgroup\$ – jsotola May 23 '18 at 23:31
  • \$\begingroup\$ I think the preferred method is to use a raspberry pi, and a camera and image the fuse, and upload to a cloud AI platform for recognition. Cost Down: Put both fuses where a single camera can see them \$\endgroup\$ – Henry Crun May 24 '18 at 0:30
5
\$\begingroup\$

If you can live with a bit of leakage through a blown fuse, and there is always a reasonably low value load, put one optoisolator LED across the fuse (with a resistor in series, of course, and an inverse diode across the LED wouldn't hurt).

Otherwise you could do something like this:

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
2
\$\begingroup\$

You need a way to differentiate between 3 current levels:

  • 0 when +12 is faulty
  • I/10 when fuse is blown
  • I when fuse is OK

eg use two different pullup resistors, or use an ADC input

The key design issue is that there has to be a large ratio between the two currents as you have to allow for variation in +12V, Opto Current Transfer ratio from unit to unit, and over temperature, and port pin threshold.

schematic

simulate this circuit – Schematic created using CircuitLab

Of course this is assuming you need isolation. If they have a common ground then its trivial...

schematic

simulate this circuit

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.