CB CNC Part 10 / NPN Proximity Limit Sensors

Ok I’m going to wire the DC power to the controller because I haven’t turned it on and I should check it actually works. And then what I’m going to do is start thinking about how to assemble the proximity sensors.

These are normally open NPN sensors which I bought from ebay.

I was recommended these types by Hayri who makes the controller board I am using for this project.

I want to use two on either side of the x and y axis of my CNC machine so I can scan the margin and determine the available cutting distance between them.

I know some controllers have pins for the minimum and maximum limits but the control board I am using only has single inputs for all the axis – so I am hoping there is a way of wiring the sensors in parallel to each individual input.

Anyway that’s a problem for another video.

These types of sensors seem to be the go to ones for 3D printer owners who have decided to add a bed-level feature to their machines – so there is lots of information online about wiring them.

But before I do this, I will power up the control board for the first time.

I’m going to wire this a little bit longer then I obviously need, and then I’ll cut it down.

After I’ve done this I will wire the proximity sensors to a 12v LED switch. I want to progress in stages, so I will temporarily wire up a single sensor using crocodile clips, which when activated will power an LED. Then wire two sensors in series – meaning one sensor must be activated before the second. And finally in parallel so either switch can be activated independently of the other.

Anyway let’s see if this lovely control board turns on.

Let me check – 24v and that’s set to 24v. Now powering up the driver. Wow it’s receiving power and that is a really fucking bright LED.

OK I’ve just wired up the proximity sensor and it’s an NPN, normally open. And I’ve done it based on this diagram. So I’m using a 12v bulb in the switch which should light up when something is detected in front of the proximity sensor. I’ll just tape these down a bit just so they’re not… maybe I should have used a terminal block. So the blue wire is going to the negative, the black wire goes to the bulb, the brown wire goes to the bulb and then to the positive. So I’m just going to turn this on now. Metal, wow that worked, can’t believe it. That worked first time.

Now I’m going to try wire up two sensors in series. Ok so I’ve wired, this looks like a complete mess but I’ve wired this diagram here now. The only difference I’ve done, as far as I could tell from this diagram is instead of daisy chaining the power, 12v power from the load I’ve gone straight from the power supply unit. I better check everything. Live comes out and goes to the brown on sensor one, and to the brown on sensor two. So I’m imagining that’s minimum and maximum. Then live goes into the bulb which I’m going to use as the load, and then goes to the black on sensor one, which is there. Then I connect blue which is the ground to black which is the signal on sensor two, and then the ground goes to negative. Ok here goes, two metal objects in front of both.

Ok I think I’ve widdiddit, why did did it, why did I do it? Ok this is wired in parallel, I don’t think I’ve made any mistakes but there is only one way to find out. Ok that good, that’s what I want.

When they are both pressed?

Ok what I need to do now is connect these to my driver board and the signal needs to be five volts or less, otherwise I could fry this very nice piece of electronics here.

I began thinking about different methods to do this, including using relays or even wiring the signal through a voltage regulator but in the end both Nathan (from OpenTronic) and Hayri (who makes the Phonix CNC controller) suggested using a voltage divider.

As I said earlier the particular sensors I am using are popular amongst 3D printer owners and there were some sources online to suggest how to do this. I borrowed a 10 and 15 kohm resistor from Nathan and wired this into the circuit – pulling the coltage down from 12v to just under 4v.

So ignore the colour coordination but this wire should be the signal and this one should be the ground. So I’ve put something in front of the proximity sensor.

When I put a piece of metal in front of the proximity sensor you can see this goes to 0 – which is the active low.

One additional thing I noticed was for the sensor LED to work I had to wire the ground back to the PSU and not the controller. I wanted to plug the controller into my laptop and simulate a homing sequence but as I had not wired any other components this didn’t seem to work.

Anyway in the next video I am going to assemble a pretty interesting looking enclosure, and begin the process of laying-out the components.  Thanks again for watching.



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