Arduino Forum

Using Arduino => Sensors => Topic started by: bobleon on Jun 04, 2015, 05:41 pm

Title: NPN sensor signal> Arduino UNO; seeking a solution for novices
Post by: bobleon on Jun 04, 2015, 05:41 pm
I'm looking for a solution that will not damage the Arduino board…nor tax my ability to get up to speed on electronic circuit design. In other words I am looking for a sort of layperson's solution. I need to optimize time a lot more than money. Eventually maybe… but for now I don't care if designing a circuit myself will make it cheaper…ie I don't mind BUYING a solution. (I'm controlling indexing on a machine not selling PCB boards)

I've not spent a great deal of time researching this…maybe a half day or so but for ONE input signal that about exhausts my exuberance for the details. (I'm used to a PLC doing much of the signal conditioning and voltage regulating for me)
I have learned that a basic step is voltage dividing. But I have also heard caveats..and seen flaming resistors ….in what if scenario's.

I've also learned that a well placed Zener Diode (in parallel with the output…facing which way?) will reduce the risks…sort of, maybe….cuz then I hear that there are Knee curves and max operating currents that will also burn out zener diodes or render them moot. So maybe  just buy a voltage regulator …but then what is with the capacitors needed? Plus how long will it take to  take delivery on all this stuff...and how many iteratioins of two day shipping?  It is all a bit much for my puny electronic brain (I only play a wizard on TV…and then it is  more OM than OHM )

I had a similar experience on the OUTPUT side…I had trouble getting the relay that came with the Vilros starter Kit to work, I had the diode and transistor installed and checked it twice twice..but no dice.   I solved that one by buying a SainSmart relay module..they took care of all the signal amplifying.

Anyway…I have a 10-30v NPN sensor (I'm under the impression that PNP is more complicated/risky) I will power with 12v…and I'm looking for the 'prosumer' solution for inputting my brand new Arduino UNO…which I would like to NOT blow up.

Detroit manufacturer with production looming  

Title: Re: NPN sensor signal> Arduino UNO; seeking a solution for novices
Post by: Archibald on Jun 04, 2015, 09:04 pm
If your sensor has an open-collector NPN transistor output as this ( (on the left), then you can connect your Arduino input to point 'A'.

The resistor R is not necessary if you use a pull-up resistor within your Arduino chip. See the "Pins Configured as INPUT_PULLUP" section here (
Title: Re: NPN sensor signal> Arduino UNO; seeking a solution for novices
Post by: dlloyd on Jun 05, 2015, 03:03 pm
What we're lacking is the specific sensor you're using. Some sensors with NPN outputs have an internal pullup resistor to the power ( This would change how you would interface the signal to the Arduino. Also knowing if the Arduino is 3.3V or 5V would be helpful.