 # Proximity Sensor LJ12A3-4-Z/BX

Proximity Sensor LJ12A3-4-Z/BX
Has any one used this sensor? I read the specs and it cautions that the Ramp board wants a signal voltage of less than 5 volts. They recommend adding a 15 ohm and 10 ohm resistor to reduce the current voltage to 3.5 or so . When I test the sensor using a 12 volt input and setting a metal plate on the tip I only get 2.2 volts on the output side without even adding the resistor circuit. Is this just a bad sensor? I have tried several things but nothing works… if I increase the input to 20 volts I can get close to 3.6 volts signal but my power supply is only 12 volts. Any suggestions?

If your using 12V in, you should be seeing 12V out from the sensor. The Ramps/Arduino is using 5V logic, so you don’t want to put over 5V on an input pin. The Arduino input pin will read a logic TRUE, or HIGH if the voltage is between 2.5V and 5V. It will be FALSE, or LOW if it’s less than 2.5V. I’m sure they recommend dividing the voltage for a 3.5V HIGH signal to be safe.

It sounds like your sensor may not be working right. Double check the wiring diagram, the wire colors on these sensors are a bit different.

Dave

Hi Dave - sorry for the long pause in response - I was building a table and heated work surface. I have used the resistor circuit using a 15 ohm resistor and a 10 ohm cross over to the ground I get 6.4 volts from the signal pin for the ramps. I need a resistor combination that will cut the voltage to less than 5 volts but don’t know enough to change the values.
I have tried several combinations and always get around 6.4 volts which is too much. I don’t understand the basic concept of a resistor bridge and need help to solve it…
Rand

If your input voltage is 12V, you should be seeing 4.8V across the 10 ohm resistor and 7.2V across the 15 ohm resistor. Make sure you didn’t mix up the resistors. Check the voltage across each resistor. One voltage should be lower than the other. What voltage reading are you getting on each resistor?

I would suggest using larger resistors like 15k ohm (15,000 ohm) and 10k ohm (10,000 ohm). The larger resistors will reduce the current.

If you have a good picture of how you have this wired may help.

Dave