New Build, Aluminium Frame Router/Mill

**Clive S** · 13-03-2016

These switches cannot be used for combined homing/limits

I don't think it is right to condemn the switches and say they don't work for combined use. Lots of people use them it all depends how they are wired. NPN and PNP are different and have to be wired different.

**JAZZCNC** · 13-03-2016

Dave these switches 100% do work for both I use them all the time. It's either your using them wrong or possible the BOB doesn't work like you think.?

How you have worked around the problem may well work but I wouldn't trust for repeatabilty.

I think the answer to the problem is you'll need to use 10k resistor to force the input high.

**Davek0974** · 13-03-2016

ok, but the inputs are already pulled high internally by 4k7 so surely another pull-up would be bad??

You can see the LED on the sensor flickering unless the tip is 100% covered by the target, this does not match my previous experience of inductive sensors where they are either on or off - NO flickering!

This is not a PNP/NPN issue, these are NPN and wired for NPN normally open.

JAZZ, you use sensors, does the LED flicker?

here's a video...
https://youtu.be/S5PP5sQh5Vk

**JAZZCNC** · 13-03-2016

Even the super cheap Ebay ones work ok dave.

You haven't wired the switch powers in series have you.? That flickering looks like struggling for volts.!

**Davek0974** · 13-03-2016

Originally Posted by JAZZCNC

Even the super cheap Ebay ones work ok dave.

You haven't wired the switch powers in series have you.? That flickering looks like struggling for volts.!

Hi

No, all wired in parallel as described in manual, I have a quality bench psu and will test them on that now...

If you fully cover the end with the target the LED is solid on, but mach picks up the very first flicker and takes that as the position, as expected.

Maybe these are fakes or junk clones which have the output conditioning circuit missing??

**JAZZCNC** · 13-03-2016

Nah I'd be suspecting the conflict between swithc and BOB my self. The input isn't conditioned correctly. Stick a 10K resistor on between 12v and pin 10.
Worst case is it will slow down the input reaction time.

I've had this before with prox switches and PMDX board using ESS.

**Davek0974** · 13-03-2016

Thanks Jazz, I have some updates..

This seems to be a PSU issue believe it or not!

The BOB is powered from a little 15v SMPS, the sensors are powered from the BOB which has a DC-DC converter and puts out 12v.

First test was to put a sensor on my variable bench PSU, they worked perfectly! Clean on and off LED - perfect.

So i tried running the sensors direct from the 15v PSU - these are NPN so supply voltage does not affect the output signal and the 0v in/out is common on the BOB - result was that it worked ok UNTIL I took Mach out of reset when the flickering returned - baffled!

Next i tried running the BOB from the bench PSU - perfect result and i could even enable the limits (on one axis anyway) and it all worked as I first expected it should.

So - do we have a duff PSU, are these sensors sensitive to SMPS output?
I am not sure what to try now - baffled.

Maybe add some uF to the output of the supply and maybe some filtering?
I might get the 'scope out and see whats on the supply.

Get a different PSU? (this one came from CNC4YOU as did the BOB)

Here's another oddity - the plasma always wipes out the radio as soon as the drives are enabled, now it seems this build does the same - as soon as the drives kick in, the radio gets washed out.

Both builds use SMPS and all parts came from CNC4YOU. Food for thought.

**Davek0974** · 13-03-2016

Originally Posted by Clive S

I don't think it is right to condemn the switches and say they don't work for combined use. Lots of people use them it all depends how they are wired. NPN and PNP are different and have to be wired different.

I didn't mean "these" as in all sensors, just maybe these super cheap eBay ones possibly, they were only £2.50ea. Previous experience was that the LED & output was either ON or OFF, not flickering depending on how close the target is.

**Clive S** · 13-03-2016

Originally Posted by Davek0974

I didn't mean "these" as in all sensors, just maybe these super cheap eBay ones possibly, they were only £2.50ea. Previous experience was that the LED & output was either ON or OFF, not flickering depending on how close the target is.

You got robbed you can buy them for about £1.30 on ebay. I think you might be correct with the pull ups in that case I think you will need PNP sensors. But that doesn't mean they are crap.