Can I return a 12v to the endstop signal?

I have a capacitive NPN sensor I want to use as a bed probe, it needs a 12v supply voltage and returns a 12v signal. I'm wondering if I can just power the sensor directly from 12v instead of from the pin headers and return a 12v signal to the board but I'm worried this might fry the Arduino. If that's the case I will make up a zener diode voltage regulator for the signal.
Any thoughts?

Arduino mega input pins are 5v max, definitely do not put 12v into it

Yes, applying 12V is one of the few possible ways to fry an ATmega. A resistor-based voltage divider would be another way to get voltage down.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

Also, make sure that wherever your 5 volts is coming from has a common ground with the Arduino.

Thanks for the answers.
Jbernardis I'm not entirely sure what you mean common ground, the 12v will be coming from a source outwith the arduino but will be connected to the ramps board. I've attached a little circuit diagram of what I'm planning.endstop.pdf The dotted line would connect the ground for the ground pin on the Ramps board to the ground on my power supply, but I'm not sure if that is safe.

Edited 1 time(s). Last edit at 07/18/2014 06:10PM by blabberjack.

I'm not sure I fully follow the diagram, but you can't pick up a single piece of wire and say it is at 12 volts. Voltage is a difference in potential - you can hold up two pieces of wire and say there are 12 volts of difference between them. Normally when you use voltage on a single wire, you are implying a difference to ground. However if you have two separate circuits, their grounds are not necessarily at the same level, so if you interconnect them with a single wire, the voltage on that wire is undefined. Normally this is overcome by physically tying the grounds together so now the voltages are all relative to the same standard.

I'm not sure I fully follow the diagram, but you can't pick up a single piece of wire and say it is at 12 volts. Voltage is a difference in potential - you can hold up two pieces of wire and say there are 12 volts of difference between them. Normally when you use voltage on a single wire, you are implying a difference to ground. However if you have two separate circuits, their grounds are not necessarily at the same level, so if you interconnect them with a single wire, the voltage on that wire is undefined. Normally this is overcome by physically tying the grounds together so now the voltages are all relative to the same standard.

It's been a long time since I did circuit diagrams in school but we were always taught to draw voltage rails with the potential difference and ground, that's what I've got here, the top bar is my 12v rail and the bottom is the ground, the potential difference between them is 12v.
The pin headers for endstops on the ramps board have a +v and a ground pin as well as a signal, what I am proposing is tieing the ground pin to the ground on my 12v psu.

That's what I thought you were showing, but I wasn't certain. That should be OK as long as, as the others have mentioned, you limit your voltage to 5 volts.

I've got all the mechanical stuff done now so I'm looking at the electronics and I've found that the signal output from the capacitive sensor is 5.7v is this too high to feed into the ramps endstop pin?