12v5vopto-isolatorpicproximity-sensor
I have got a LJ12A3-4-Z/BX Inductive Proximity Sensor Switch NPN DC6-36V with this Specifications:
(I use 12V or 8V to supply one sensor)
this should be connected to this ports of a pic (one sensor per limit):
what do I need optocouplers etc.?
If your power supply is indeed the issue, then add a simple low pass filter in your power supply connections as close to the sensor as possible. I'd start with the following configuration to see if it improves the situation. Double check if Vcc at the sensor is 4V5 - 7V.
simulate this circuit – Schematic created using CircuitLab
Assuming that the device is powered by Arduino's 5V and assuming that the device is drawing 30mA of current, the voltage accros R1 will be 0.3V and the supply voltage for the sensor will be 4.7V, sufficient according to the datasheet. R1 and C1/C2 form a simple low pass filter that will suppress high frequency noise from the power supply.
Keep wires as short as possible, keep them as close together as possible. If possible twist the wires for the power supply and twist the wires (V(out) and GND) for the output.
A few suggestions:
Lets assume that there is only a wire/ metal strip buried beneath the ground (not very deep) as the 'invisible' boundary.
(1) The wire/strip has a direct current passing through it.
You could detect the magnetic field around the wire with a Hall sensor.
(2) The wire/strip has a low frequency alternating current.
Hall sensor or pick up coil (detecting AC 'hum')
(3) The wire/strip has a high frequency alternating current
Tuned LC circuit - probably with a ferrite rod to localize signal.
(4) The wire/strip is carrying a pulse signal (e.g. output of a square wave generator)
as per solution (3) but doesn't need to be tuned (detects wideband 'noise') - similar to electric cable detector in walls.
(5) The wire/strip is not connected to anything
Some form of metal detector.
Best Answer
You can use an optocoupler as follows:
simulate this circuit – Schematic created using CircuitLab
Choose an optoisolator that has more that sufficient CTR such as a TLP291-4(GB,E).
You can get such optoisolators 4 to a package, so only two would be required. The 12V supply that powers the proximity detectors does not need to share a ground (and probably should not share a ground) with the microcontroller.
Edit: If you want a through-hole package, one suitable type is the TLP624-4(F)