12v5varduinodigital-logictransistors
I have an inductance sensor on a CNC machine that goes 12V high when triggered (open collector when not) . I want to read that input on my arduino who uses 5V logic.
I was thinking I could just use a simple NPN transistor to do the logic level shifting. Would this work? I dont want to test it incase it could fry the arduino.
3.3 volts > 1.4 volts. So 3.3 volts should keep it shut off.
But for more confusion see also note 5. The two sentences seem contradictory to me.
EDIT: Here's a pic of what I'm talking about. Push-pull totem output is internal to the microprocessor. You should reduce \$R_{FA}\$ by the output resistance of the totem pole, which is in the vicinity of 25 ohms. It's in the micro's datasheet.
I think what you're really after is an IO expander: http://www.digikey.com/product-detail/en/SX1505I087TRT/SX1505I087CT-ND/2272323
It's a relatively simple digital device. The Arduino would communicate with the IO expander over some standard communication protocol (typically I2C or SPI), and the IO expander wiggles pins on behalf of the controller.
Instead of using 12 pins on the Arduino to directly control the H bridges, the Arduino uses 2 pins (in the case of I2C) to communicate with the IO expander, and the IO expander directly controls the pins. The Arduino would say "Okay Mr. IO Expander. Turn on your pin2 and switch off your pin8", and the IO expander would set those pins accordingly.
Best Answer
It will work. This circuit should be at logic 1 if there is no signal and at logic 0 if there is 12V signal present.
P.S. 10K resistors are just there as a generic value. For this purpose you can use almost anything. Base-ground resistor is 100K as recommended by @Russell.