Centroid Community CNC Support Forum

Hello,

I'm getting ready to convert my mill from Mach3 to Acorn. I'm trying to finalize the wiring for my tool setter and touch plate. I want to use one input for both. The tool setter is NC and obviously the touch plate is NO. I looked through my electronics box and found a IRL510 NFET. Here's the schematic I came up with.


Anyone see any issues here?

Thanks,


Chris

That won't work at all. I suspect you are hoping to turn the FET on and off with the probe but a N channel MOSFET won't switch with the circuit shown. Looks as if you are hoping for a low signal when the probe is active, so no signal inversion is required - in which case, why the FET?

If you are trying to invert the signal, move the resistor from the bottom (source) to the top (drain) of the FET and take the output from the top of the FET.

You should always fit a series resistor between the gate and external connections, along with a decoupling cap (gate to source, perhaps 100nF) and limit the gate voltage to 10V or so. 20V isn't ideal, as lifetime is affected by peak gate voltage.

Sorry - rushed answer - lunch time!

Here is a schematic for a tool setter (Check out all the Centroid Schematics)
Understand that Acorn inputs are standing at +24VDC to activate the input, you simply ground it with COM from the Acorn power supply.
Be sure you connect one of the 24V terminals on the input to Acorn Power Supply +24VDC
Sensors used (Proximity/Hall Effect etc.) need to be NPN and should be Normally Closed.

If you have purchased touch plate/probe post pictures/manual here. We can "See" what you "See" more information you provide, the better suggestions we can make.

Marty

Marty,

I completely missed that the inputs were all standing at +24V. Thank you for pointing that out.

I bought a cheap tool setter off eBay. The instructions are in Chinese so they are pretty useless. The instructions even mention an LED that doesn't exist on the unit I received. I used my meter to deduce that it has two NC switches, one for tool touch off and one for overtravel. They are parallel circuits.

I've been using an insulated PCB board as a touch off plate for the work offset. In Mach3 I had the machine grounded and the probe went to an active low input. The schematic you posted is basically what I used for my touch plate in Mach3.

Here's rev 2 of the schematic:

Muzzer,

Thank you for your input. It's been 25 years since I was in tech school. I haven't designed any circuits in years.

Yes, I was trying to invert the signal from the touch plate. I think I have it now. Please take a look at the rev 2 schematic in the post above.


Chris

Muzzer wrote: ↑Thu Jan 07, 2021 9:42 am That won't work at all.

Quick update. I got the circuit assembled and it works.

ChrisAttebery wrote: ↑Wed Jan 13, 2021 10:58 am Quick update. I got the circuit assembled and it works.

All good then?
Marty

That looks better and as you say, it works!

Really you should add a noise decoupling cap directly across gate to source (ground) to clean up the operation and provide some protection against electrostatic discharge. A decent quality 100nF or so ceramic cap would be a good choice. The electrical contact against and through the tool will actually be pretty noisy and those FETs don't like much voltage on the gate, so are easily killed by an ESD zap. The cap will gobble much of the ESD energy and give a cleaner change of state. The failure mode in a FET due to ESD damage is a damaged gate, leaving you with a FET that won't turn on. That could cause a tool crash when you are trying to touch off.

Now that I've got the circuit is working I'll dig through my parts box and see what caps I can find. I'm sure I have something suitable.

Thanks for your help,


Chris

Muzzer wrote: ↑Wed Jan 13, 2021 2:10 pm That looks better and as you say, it works!

Really you should add a noise decoupling cap directly across gate to source (ground) to clean up the operation and provide some protection against electrostatic discharge. A decent quality 100nF or so ceramic cap would be a good choice. The electrical contact against and through the tool will actually be pretty noisy and those FETs don't like much voltage on the gate, so are easily killed by an ESD zap. The cap will gobble much of the ESD energy and give a cleaner change of state. The failure mode in a FET due to ESD damage is a damaged gate, leaving you with a FET that won't turn on. That could cause a tool crash when you are trying to touch off.

martyscncgarage wrote: ↑Wed Jan 13, 2021 11:09 am All good then?
Marty

I think so. I just finished up the last batch of parts I needed to make before I could start the conversion. Hopefully I can start working on it over the weekend.

Thanks,


Chris