Inductive Proximity Sensor electronics problem, help needed.

[joel0407]

So I've bought these http://www.ebay.com.au/itm/5Pcs-PNP-...72.m2749.l2649

I thought they were pretty simple PNP senor. My Parallel Port Break Out Board (BOB) calls for a ground input on the input pins. So ve+ and Gnd to brown and blue then black to the BOB. I was a bit worried to start with because when I put my meter from ve+ to the black wire, I got 300mv when not tripped and 12v when tripped. Obviously showing a ground leak and getting 300mv when not tripped. I thought it might show as being tripped all the time. Unfortunately, it doesn't show tripped at all.

So this is what I have:

Senor tripped. I get 12v between ground supplied by the sensor and ve+. (thought that proved ground on the wire from the sensor)

Hook that same wire from the senor to the BOB and nothing is seen. (something is wrong)

Use a jumper wire directly from ground to the BOB (proves the BOB is working correctly and can see ground)

I know someone is going to suggest using a relay but I don't think it should be necessary and the delay for a mechanical relay to trip may affect home accuracy.

Thanks in advance to whatever advice is given.

Happy Days

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[manofmanyhats]

Does your BOB have optoisolation on the input pins you're using? Is it designed to take a 12v signal if not?

[Al_The_Man]

Those are PNP NC so when non-tripped (off) they will switch the output to +ve, when tripped they will open and the output becomes 0v.
These are sourcing devices and require a Sinking type BOB.
Depending on your BOB input you may need a 1k resistor from output to GND.
You need to know the nature of the input your BOB has
Al.

[joel0407]

Does your BOB have optoisolation on the input pins you're using? Is it designed to take a 12v signal if not?

Yes, I believe it does have photocouplers on the inputs.

[joel0407]

This is the BOB.

https://warp9td.com/images/BOB_Vendo...line/ST-V2.pdf

- - - Updated - - -

This is the BOB.

https://warp9td.com/images/BOB_Vendors/StepperOnline/ST-V2.pdf

[joel0407]

Those are PNP NC so when non-tripped (off) they will switch the output to +ve, when tripped they will open and the output becomes 0v.
These are sourcing devices and require a Sinking type BOB.
Depending on your BOB input you may need a 1k resistor from output to GND.
You need to know the nature of the input your BOB has
Al.

Can you elaborate on Sinking type?

Won't putting a resistor between GND and the input be enough for the input to see a signal?

[Al_The_Man]

The BOB is apparently a sink type input, if so the source sensors you have should be OK, just that they should switch the input on with no signal, being a NC device output.
It looks like opto's on the inputs, it would be nice if these DIY suppliers showed details of the actual input, it is not like this method is a proprietary secret!!
Here is a PDF of sink source details.
You shouldn't need any resistor if it is the input I suspect it is.
Al.

[manofmanyhats]

Do you have a setting for active low/high in your control software? In mach 3, you would need to check active lo for that pin in the ports and pins menu.

Also, on my system, I had to tie the V- of the powersupply for the sensors to the v- of the powersupply to the BOB/drivers for it to work correctly. I use NPN Normally Open though. Hopefully someone more knowledgeable than me could chime in on that.

[Al_The_Man]

Where a BOB has common opto-isolator input.generally only two wires are needed from a 3 wire prox, = signal and common connection, whether it be +ve or common (GND) (Sink or Source input)..
The prox itself still requires 3 conductors connected. and can be supplied from the BOB if necessary.
With NPN that would be normal for one conductor = input and the common connected to the of the BOB common.
If enough buyers of these BOB's would get on the makers of them to supply more info on the input, and if not I would tell them I am not purchasing their product.
Al.

[joel0407]

So I wired up a spare senor as pictured. 12v from the BOB 12v, senor wire directly to the input and it doesn't work.



I'm guessing some resistors are going to be needed.

[joel0407]

I'm also searching around for the answer.

Like here :http://www.cnczone.com/forums/diy-cn...-switches.html

[joel0407]

Yep so confirmed again. Putting the common ground on the input is seen in LinuxCNC.

[joel0407]

Those are PNP NC so when non-tripped (off) they will switch the output to +ve, when tripped they will open and the output becomes 0v.
These are sourcing devices and require a Sinking type BOB.
Depending on your BOB input you may need a 1k resistor from output to GND.
You need to know the nature of the input your BOB has
Al.

I should have paid more attention to this post.

Or maybe I just didn't understand it then. Yes, so I think I have a sourcing type BOB. So not sure how to get this to work with PNP sensor.

[john-100]

Hi Joel

yesterday I collected together various breakout board circuits I had reverse engineered to answer posts in the past

this is your BOB :-



you could connect the output of your limit switches to a NPN transistor (with a resistor to limit the base current )
to convert the current sourcing switch output to a a current sinking output

would you construct your own adaptor or be looking for a ready made adaptor ??



John

[joel0407]

If the inputs are opto isolators with a internal series resistor set for 5v operation, you could simple measure the current the opto is set for by inputing 5vdc and measure the current, then wire a suitably calculated resistor in series from the collector to input based on the difference ~7v or just under.
Assuming open collector prox.
Al.

Hey Al,

I found this post from you on another thread here: http://www.cnczone.com/forums/genera...nsors-bob.html

So meter on amps. Then connect from ground to input and check current and voltage.

Connect input to ground with a resister calculated with voltage and current.

Connect collector to the input via a resistor. I already know the collector voltage is 12v. Calculate the resistor to be the same watt value as the other resistor.

So in theory the voltage a the input when the collector is on should be zero as whatever voltage/current is provided by the collector is dumped to ground via that resistor?

Although I might have the terminology all messed up, is the idea correct?

[joel0407]

Hi Joel

yesterday I collected together various breakout board circuits I had reverse engineered to answer posts in the past

this is your BOB :-



you could connect the output of your limit switches to a NPN transistor (with a resistor to limit the base current )
to convert the current sourcing switch output to a a current sinking output

would you construct your own adaptor or be looking for a ready made adaptor ??



John

Thanks John.

Just what I need but complicated looking. I don't know how I can make that neat in my box. I have a few transistors here that I might try to set up temporarily then order some NPN sensors.

[joel0407]

I just bought these: 5Pcs New LJ12A3-4-Z/BX Inductive Proximity Sensor Switch NPN NO DC6V-36V | eBay

Should fix my problem.

Thanks for all the help guys. If it was as simple as I thought with just 2 resistors one from ground and another from the collector then I' do that but I think it'll get a bit messy with 4 transistors and 8 resistors all before my BOB.

I'll get back to working on why my 2 motors travel at different speeds when homing.

Still don't understand why I get 12v between the collector and + if the collector is +?

Happy Days

[john-100]

Hi Joel

the new NPN proximity sensors are the easy solution

just for information
a ULN2804A IC has 8 NPN darlington transistors and resistors in one package and could be an alternative to the circuit in post 14

looking at your resistor connected between the switch output and Ground

this is what I would do


the 1N4001 is to protect the opto-isolators LED
as the LED's can easily be damaged when reverse biased

john