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Topic: Controller 12V outputs & indicating fuse state (Read 127 times) previous topic - next topic


Hi all,

I am designing an [Arduino] controller for the electrics on my motorcycle. I have done a lot of searching and have managed to find separate circuits for [1] controlling the 12V outputs, [2] indicating a blown fuse, and [3] creating a 5V signal from the 12V fuse indicator circuit. But I haven't come across a complete solution, so I would appreciate any comments on what I have pulled together.

Here is a test case circuit. I would essentially have this arrangement for each output. [turn signals, horn, starter, etc...

This may seem a bit 'belt and braces', but as a running motorcycle has potential to be a noisy environment, I wanted peace of mind for any troubleshooting going forward.




Feb 15, 2019, 07:29 pm Last Edit: Feb 15, 2019, 09:06 pm by alesam
Pin 2 connection is completely wrong. When transistor from upper part of 4N25  opens it will shorten +5v to ground. As a result either transistor or power supply will blow up.

You need to connect resistor (5K-10K) between +5V and pin 5 of  4N25. And remove 4K7 resistor.


Thanks alesam,

Ha, the Pin 1 circuit as the driver for the output, was the part I was most comfortable with.

Here is my thought process...

When pin 1 is set high, pins 5 & 6 of the 4N25 are closed, in turn connecting the collector and emitter of the TIP125, in turn connecting the load to ground. (sounding the horn, light, turn signal or whatever)

That is all fine until the fuse blows for some reason... in which case BC558A is pulled closed, connecting pins 5 &6 of the upper 4N25, which in turn pulls pin 2 high. (Indicating a blown fuse)

I realise mirroring the 2 4N25's in the diagram is probably going against draughting protocol, but does my theory make sense?


Sorry, its a typo. I was talking about Pin 2 .

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