Thread: Triac PC Linuxcnc
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19-06-2022 #11
Certainly can be made to work, however, bear in mind the switching time for the relay(s) - guessing in the order of 5-10ms (I'll let you do the math on that). Place a series resistor in line with the +supply of the sensor, ground-to-ground. That gives you a monitor point at the supply terminal of the sensor that is the input into the comparator. Choose the 24V flavour of the comparator board and it's all pretty straight forward. The choice of series resistor needs a little consideration - I'd start with a 100R - if (my assumption) the sensor is a switched constant current sink of 1mA / 200mA then that would give a switching voltage swing of 23.9V down to 4V at the sensor supply line.
It's a bit of a sledgehammer solution but it provides all the function that you need in a very handy prebuilt module. If it's affordable to you then it's a valid solution.
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20-06-2022 #12
Great checked those sensors this morning. They are feed by 12v. If there is no metal near the sensor, it's at about ,8.5v. when metal is near it, it's at about 10.5-11v
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20-06-2022 #13
Axis control with Linuxcnc
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25-06-2022 #14
Waiting on some parts to come to tackle the homing sensors.
I need a bit of help with the Spindle. I have the spindle working by grounding the SGR relay and hooking up a 9v battery (it's at about 4v) and it's spinning fine. My issue the spindle control board is not isolated.
I have the BOB feed with the machine cabinets 24v power. On the Bob it has a 0-10v opto isolated output for spindles. I'm afraid to connect this incase I blow something. Would changing the power feed to the Bob from separate transformer power supply isolate it ? The BOB I have is the same as below.
MACH3V2.1
https://a.aliexpress.com/_uzGXviLast edited by JohnT; 25-06-2022 at 05:15 PM.
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27-06-2022 #15
John, I've looked at the link to that board and I can't work it out - but it looks probable (PCB underside image) that the 0V reference for the 0-10V analogue output is common with the other 0V references on the board. In that case - I understand your concern with effectively raising the 0V reference to some hundreds of volts that the Spindle Controller operates. If that 0V cannot be isolated (between the logic and the analogue output) then, yes, you have a problem. I understand your argument of adding an isolation transformer to allow the 0V rail to be raised to that of the spindle-controller, but - of course - at that point you're raising the common 0v reference, back to the logic supply and ergo the short-circuit hazard remains at the point that you connect to another system - the connecting PC. It crossed my mind whether you could do the opposite and provide an isolation transformer (1:1) to the supply to the spindle controller, but you would wonder if there's any internal bonding of earths to line neutral anywhere on the spindle controller - either direct or indirect through EMF caps. Considerable care is needed going in this direction.
These https://www.amazon.co.uk/Isolation-Q.../dp/B082NXR4PR look interesting and useful. I've no experience of them, but understand the description rather better than the BOB.
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27-06-2022 #16
Thanks Doody. Yes I checked with a multimeter and the Bob shares it's grounds. I was looking at those isolation boards. I checked the motor controller and measured the 0-10v terminals against each other and to machine ground. I'm getting 270v DC and 9v AC with the multimeter. I don't have an oscilloscope. I'm leaning towards ordering one of those isolation boards. But if it doesn't work I could blow the motor controller etc. I'm thinking feeding one end of the isolation board to the 0-10v terminals on the motor controller and the other end to the 0-10v output on the Bob. Use a transformer power supply to feed the vcc and ground. Or else not risk it and let linuxcnc control the SGR relay and use a potentiometer to control the speed.
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27-06-2022 #17
From what I squinted at with that particular board the circuitry was visible separate from the LV and HV sides. You’d supply the LV from the general machine supplies and the HV from the reference voltage provided by (most) spindle controllers (is these that you’d otherwise write a speed control pot to). It’s low risk and you can test with a meter easily. I wouldn’t have much fear of going this route.
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27-06-2022 #18
I'll order one and give it a try. I'll hook up 24v from the machine cabinets PSU. And the 0-10v from the Bob to input 1.(LV side). For the HV side, it looks like the terminal for 0-10v connects to the output 1. The power and ground come from another isolated power source?
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27-06-2022 #19
If you was to write a pot on the spindle controller, you should have 3 pins on the spindle controller to attach to, what are those? Likely a good candidate for the HV supply side (and the pot input)
Sorry, reading on phone during demo at work, can’t review the full thread here. What is the spindle controller model?
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27-06-2022 #20
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