Sensing 12V?

Hugh

Greetings,

I am looking at a potential new project based on a protoboard. Because it involves sensing the position of a switch or two on a vehicle, I need to be able to sense the presence (or not) of 12V DC.

Dare I go down some simple route involving resistors, or am I staring down the barrel of opto-isolators, etc.?

Advice, opinions and experiences (good or bad) gladly received,

Thanks in advance,

Hugh

Mike Green

There's a recent thread in the Sensors forum on reading a rain gauge's switch closures with a Propeller in a 12V or 24V environment. The same suggestions apply in your case.

Automobile electrical systems are very very noisy. Be sure to use adequate filtering and shielding if you want to run the Protoboard off the +13.8V power supply of the auto.

Rayman

I'd just use a resistive divider to bring that 12V down to something like 2.5 V... You could use big value resistors to prevent damage to the Prop...

Hugh

Thanks Gents,

Onward and upward!

Hugh

Mark_T

Rayman wrote: »

I'd just use a resistive divider to bring that 12V down to something like 2.5 V... You could use big value resistors to prevent damage to the Prop...

No, I don't reckon that's enough protection, expect big inductive spikes on the 12V line (I mean BIG) and use schottky diodes to prevent the pin going above 3V3 or below 0V Remember the 12V system is connected to many largish electric motors and inductors (the horn for instance). So perhaps 47k/10k divider and two schottky diodes per pin, then possibly a schmidt-trigger to condition the signal. And even then debouncing in software would be wise.

Cluso99

With the potential for spikes, a cheap opto and two resistors would be simpler and safer, IMHO.

kwinn

Cluso99 wrote: »

With the potential for spikes, a cheap opto and two resistors would be simpler and safer, IMHO.

Ditto. Also with Mike's comment. A good choke ahead of the filter and PS caps helps a lot as well.