Detecting activation of a low-side switch using a microcontroller

[danners430]

Afternoon ladies and gents,

I'm trying to work out a way to connect a microcontroller to a DCC decoder's accessory outputs. The problem is, decoders use low-side switching of accessories, with a common positive rail. Is there a way to detect the activation of the low-side switch using the micro, or is external circuitry required?

Cheers!

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[fourtytwo42]

Your expecting everybody here to be a railway enthusiast then, if you want answers best not to post TLA's nobody knows! Fortunatly I know as I am a railway enthusiast!, I would imagine you will need external circuitry as the load being switched is probably supplied by a reletevly (in mpu terms) high voltage so if connected directly will blow up your mpu. For example if the load is supplied by +12V then you will need a series resistor and zener diode to limit the voltage swing to within the rateing of your mpu/micro.

[danners430]

Your expecting everybody here to be a railway enthusiast then, if you want answers best not to post TLA's nobody knows! Fortunatly I know as I am a railway enthusiast!, I would imagine you will need external circuitry as the load being switched is probably supplied by a reletevly (in mpu terms) high voltage so if connected directly will blow up your mpu. For example if the load is supplied by +12V then you will need a series resistor and zener diode to limit the voltage swing to within the rateing of your mpu/micro.

The main question is actually nothing to do with railways, I just added that for context.

The main question is how to detect the switching of a low-side switch using a microcontroller, as a low-side switch obviously doesn't supply a nice +5V logic signal.

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[james_s]

You could use an opto-coupler, anything that can be made to light an LED can then be interfaced to an IO pin on a microcontroller.

[danners430]

You could use an opto-coupler, anything that can be made to light an LED can then be interfaced to an IO pin on a microcontroller.

That seems logical...
Seems logical enough that I'm now kicking myself for not thinking of that [emoji23][emoji23][emoji23]

Many thanks!!!

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