DIY CNC BOB

[Robertspark]

Proximity sensor interface.

From my experience prox sensors seem to be rated 6v-36v, with up to around 300mA load current, and around 0.8 to 1.2 mA leakage current....[hence if you common 8 of them up, they can trigger the optoisolator or at least make it less noise immune]

Hence from my experience a dedicated proximity sensor board which is able to deal with noise and (high) leakage current would be good.

I run mine at 24v (for noise immunity) but am still having occasional issues as the UC motion controllers do not offer software debounce (time delay) as was offered on the Warp9 Smooth Stepper + Mach3 parallel port interface.

[cncdrive]

The UC controllers have built in RC filters on all inputs, LPT ports does not and the UCs do debounce, it is built in, just is not adjustable, however ofcourse the time constant of this is relatively low, otherwise signals would delay too much.

What about adding a terminating resistor or snubber at the input of the BOB?
I mean if the sensor can handle about 300mAmps current then you could simply add a low value power resistor in parallel with the input opto and it's resistor to load the sensor, so it will become less noise sensitive.

[Robertspark]

Balazs, thanks for the explanation,

Yes, I've got a few (can't remember how many) 2k resistors in parallel as a load. But I've got 8 sensors in parallel (2 for each axis, + 2 on y (slave axis)).... Really I need to split them up. I was going to put a 220r 3w, which will help (think the 2k resistors were 1/2w). (2k, not 2.2k, that was typed correctly)

I never had a problem with the powermax 350 transformer plasma cutter, but do have the problem with the powermax 45 igbt .....

There may be other things at play too, as they are fixed directly to the frame with metal brackets, and doing a bit of reading on prox sensors they can suffer from magnetic interference, and benefit from mounting insulators (I'm going to give them a go too), in hindsight, switches would probably be better, but couldn't find robust small switches, that require low force activation.

The prox sensors have always worked well, but I did have the debounce set very high on the smooth stepper.

I've got a few clipon ferrite cores , not tried them yet, they may help, not sure what else to try .... Bit of experimenting required...

[cncdrive]

Hi Rob,

Yes, proximity switches can be sensitive to electromagnetics.
If the issue is with that then loading the output will not help, so probably the first thing to figure out is if the sensor triggers or if the wiring picks up the interference.

And if the noise has a high frequency domain only effecting the wires then ferrits could help.