Issue with Inductive Sensor, only works once after power up

hi guys,

I have a strange problem with my HICTOP Prusa i3 machine.

I installed a LJ12A3-4-Z/BY PNP Normally Open sensor purchased on Amazon.co.uk.

I wired the sensor using the guides available, the V12 input (brown) is connected directly to the 12V + port of my RAMP 1.4 board, the output is directly solded into a 10K Ohm resistor, this is connected than to the signal going to the signal pin og the RAMP board (S) and to a second 10K Ohm Resistor bridged to the ground (blue) cable.

I initially tried with a 15 K Ohm / 10 K Ohm solution but the voltage at the ends of the second resitor was too low (2 V). Right now th evoltage, when the sensor is triggered is 4.2 V.

I found that there is quite a difference between the voltage I read at the ends of the second resistor when the sensor is triggered and not. When te sensor is open reads 2V, while when is triggered reads exactly 5V. the current is 0 mA when open and 300 mA when triggered.

I believe that the connections are correct and there is a problem with the firmware or the board itself.

What you can suggest?

Any help is welcome.

Try with a simple LM7805 regulator instead of the resistors, much simpler, reliable and cheap.

I'm waiting for the LM7805 to be delivered but I was trying to make it work in this way.

This morning I realized that the output current is flowing totally trough the ground connection and not trough the D18 pin of the RepRap board.

Will try to rewire them properly with a 10 K Ohm / 15 K Ohm configuration.

Thanks,

Vincenzo

I got the LM7805 regulators but I managed to fry three sensors and can't understandy why.

My connections are;

12V+ from the sensor to the RAMP board
GND to the V- of the RAMP board
Output to the Vin of the LM7805
GND output of the LM7805 to the V- of the RAMP board
Vout of the LM7805 to the D18 pin on the RAMP board (Zmin).


Any advice? I saw a schema and it was done exactly in this way.

My sensor is a:

LJ12A3-4-Z/BY PNP

tnx

Are you sure you have a PNP version and not a NPN version? The page from RepRap.me has both NPN and PNP under the same description of the same item, so its possible your documentation might say one thing in one page and one thing in another page.

Did you used the lm7805 without the capacitors and the diode? Specially the diode will protect the circuitry and the sensor from short circuit. Use a 1n4008 diode and a 470uf and 1uf electrolytic capacitors.

I don't know anything about the LM7805 .

But for my inductive sensor's ( 1 is the same as yours) i use 2x 10k resistors.


@PDBeal, i have a pnp and a npn, i wired them the same way, you just have to invert the signal in the firmware.
The one pictured on reprap.me is an NPN sensor, the one described a PNP

Edited 2 time(s). Last edit at 08/31/2016 10:52PM by Govahnator.

Hi guys,

just received the new sensors today and they are marked as pnp.

Will try to rewire them and let you know.

Hopefully will not fry them too, i just believe that they are really poor quality.

Test without the sensor connected. Instead a multimeter connected and you shall see the values readings most likely it fried because of a short.
Dbl check with your soldering and isolation types. Cheers