routercnc_MK3

[Graeme]

The output of an NPN switch does not have to go to the supply voltage. There is no need for additional opto-couplers or voltage dividers. A NPN output is simply just a switch to 0V.
Depending on the inputs to your BOB you have two simple options. If the input is connected to an opto-coupler then connect the anode to the BOB supply voltage (5V) and connect you proximity switch output to the cathode (may need to add a series resistor if BOB does not have one). If the BOB has a logic type input then simple connect the proximity switch output to the input. You may need to add a resistor between input and BOB supply (5V) if one does not already exist on the BOB.

[HankMcSpank]

A NPN output is simply just a switch to 0V.

The datasheet is a bit scant... I'd verify that there aren't any pull-up resistors attached to the output of that NPN switch (which would see the supply voltage on the output if the switch is in the open state)....therefore to test, just provide it with its supply voltage & see what voltage is on it output (if any)

[Clive S]

Some of these proximity switches already have a pull-up resistor inside.
Here is a good explanation of how to calculate it's value.
See page 11 http://cnc4pc.com/Tech_Docs/C50R1_user_manual.pdf in the ones I have it is 10K

..Clive

[routercnc]

Hi Graeme, HankMcSpank,

OK, that makes a bit more sense now, thank you. I'll check Hank's suggestion first - power it up without the resistor between black and brown and check the voltage on the black. If it is nothing then I have a simple switch and can follow up on your suggestions Graeme. I may need to clarify something with you but lets see what I have first.

If it is 24V then I have a pull-resistor inside the sensor and need to do something else as I know this board won't like 24V into the logic circuits!

I see Clive has posted as well so I'll have a read of his link next . . .

Thank you

[HankMcSpank]

If there is a voltage on the black, then a simple voltage divider should do....but it'd be useful for you to measure the input resistance of the follow on BOB board input pin (as that will end up being in parallel with your proposed voltage divider)....I'd imagine it'll be very high input resistance on your BOB input.

[routercnc]

If there is a voltage on the black, then a simple voltage divider should do....but it'd be useful for you to measure the input resistance of the follow on BOB board input pin (as that will end up being in parallel with your proposed voltage divider)....I'd imagine it'll be very high input resistance on your BOB input.

Checked the black wire without resistor and it was 12V (running from 12V supply for now) which means there is a resistor in the sensor and I can't wire it as a simple switch. Used method Clive posted and worked out the value as around 5k ohm

So I can work out the other resistor required to complete the divider except I need to factor in the Bob resistor

Tried to check Bob resistance across pins with multimeter (board was off) and got no reading at all. What is the method to determine this resistance

[HankMcSpank]

Checked the black wire without resistor and it was 12V (running from 12V supply for now) which means there is a resistor in the sensor and I can't wire it as a simple switch. Used method Clive posted and worked out the value as around 5k ohm

So I can work out the other resistor required to complete the divider except I need to factor in the Bob resistor

Tried to check Bob resistance across pins with multimeter (board was off) and got no reading at all. What is the method to determine this resistance

As mentioned, the BOB input resistance will likely be high ...there's nothing special involved with the measuring method - just check for resistance between the BOB input pin & BOB ground ...powered off is fine. (if you get too high a reading for your meter to detect, then to all intents & purposes the BOB input resistance can be disregarded for the purposes of your 'to be deployed' voltage divider)

What supply voltage do you eventually intend running your sensor with?

[routercnc]

I had the meter on max setting and still got no reading

Final system will be 24V when PSU arrives - testing on 12V for now