Help needed for my crash proof cnc router

[@dingolovethrob]

Hi. Electronics engineer here:- Your issue is NOISE PICKUP, so it is more to do with the IMPEDANCE of the node (input pin) that is picking up the noise. Your arduino input pin is presently very HIGH impedance as it has a HIGH VALUE resistor pulling the input pin up to 5v. To make the node less susceptible to noise, LOWER the impedance of the node. First suggestion:- disconnect the 24V stuff, just have the arduino input pin with a 220 ohm pullup to the arduino's 5v rail. (1/4 watt resistor). That will be what we call a 'stiff pullup. Noise will find it very hard to get onto that node. If it still false triggers then add a small capacitor (e.g. 100nF) from that pin to ground. The cap acts as an RF filter, a short-circuit to RF noise. Goodluck 😃

[@mickwilson127]

This would have been my suggestion too 👍

[@brucegriffiths8861]

@@mickwilson127 Shielding the lead to the aluminium foil wont he'lp unless the aluminium foil is also shielded. A grounded shield plate under but insulated from the aluminium foil may help particularly if the source is underneath the plate. This will reduce capacitive coupling from such a source to the large area of aluminium foil. High frequency pickup can be reduced by low pass filtering followed by a Schmidt trigger input..

[@CazualHaze]

Hi @dingolovethrob Great idea I love the fact you can ask people for advice and stuff like this comes back Cheers! I will give this a crack and if it does not solve the problem then I'll try an opto isolator. Cheers Again.

[@oldestnerd]

I have been working with Arduinos for several years now and also have built my own CNC machine. I agree with dingolovethrob on adding a pullup resistor and a small capacitor across the input pin of the Arduino. Having the large metal plate under the entire bed of the CNC looks to me like a very large antenna for noise pickup. Using shielded wire for all the wires in this hookup would be good except the big bed antenna undoes all that. Perhaps using an optical coupler may help. The bed could be wired with the 24 volt voltage like you have now, but use the crash signal to light the LED in the optical coupler. Connect the output of the coupler to the Arduino input with the circuit dingoloverthrob suggested. The 24 volt circuit on the bed may work better with a capacitor across the LED input of the coupler. Noise is not your friend as you've determined. I hope this might helps.

[@CazualHaze]

@oldestnerd well done making a cnc from an Arduino that's no mean feat! yeo the foil layer is a pretty good antennae. It had not occurred t me to use an opto isolator I am going to try lowering the impedance and hopefully drowning the noise first as its simpler ( I dont have an opto isolator at hand). If that does not work I will give this a try. Cheers

[@stephengrattage5219]

Have you tried a smoothing capacitor on the arduino supply? Assuming it’s on the same 24v supply. The noise could be coming through the supply. If it is on a separate supply connect the grounds together and try that.

[@CazualHaze]

HI @stephengrattage5219 The Arduino has been powered by the usb on my laptop so noise on the supply has not been an issue. I have a dc to dc converter that takes the machines 24v rail and turns it to 5v for the Arduino it looks well protected there are caps and a coil on board, time will tell! Cheers

[@fallerd]

shop lights look great! I may have missed it in the other shop videos (if so, sorry!) but I was curious if you have implemented or have plans for HVAC?

[@CazualHaze]

Hi @fallerd Shop light video coming up I am a little out of sequence with these at the moment. As always I am making it overcomplicated! I dont have plans for aircon or heating at the moment, so far its been ok in the shop temperature wise. There is a fair chunk of insulation in it, I hope the temp is quite even throughout the year when I get the lathe and mill installed stable temp does help. Cheers

[@philshel1]

My question is why? This is "cool" in theory but why the effort? Have you really crashed all the way through your spoil board? If you are really that concerned about hitting the bed, you could zero on the spoil board instead of your material (work) surface and don't machine into negative space. As far as suggestion to limit the noise you could try an opto-isolator in the line between the bed and the Arduino.

[@CazualHaze]

Hi @philshel1 Yes I have had a tool cut all the way through the old ally bed. I've had problems where the tool vibrated lower in its collet then cuts into the ally base also the controller has had a paddy now and then and plunged straight into the bed. I do use the spoil board as the base level (not yet added the spoil board to this). This is an attempt to save expensive tools more than the bed. Cheers

[@xenusceptic]

It’s over complicated just add a limit switch or better yet add a spoil board

[@CazualHaze]

Hi @xenusceptic yep it is overcomplicated and I have not yet added the spoil board. I cant see how a limit switch would work for this. I've had problems where the tool vibrated lower in its collet then cuts into the ally base also the controller has had a paddy now and then and plunged straight into the bed. Cheers

[@xenusceptic]

@@CazualHaze the idea of the spoil board is to protect the machines bed I use 18 mm mdf boards not fixed down so they can be replaced when needed and zero the tool path from the top surface of the work piece When I made my first cnc machine I was paranoid about the bit driving into the bed but in reality it’s not a problem, I fitted a bottom limit switch to my a axis but it wasn’t needed when I rebuilt my cnc I removed it as it’s not required

[@CazualHaze]

@@xenusceptic you have had better luck than me I have certainly had issues with tools walking out and even the rich auto cnc controller going off on one and plunging into the bed. I do have a set of 12mm mdf spoil boards that I have not yet fitted, time is pressing as usual. Cheers