[OddOne]

Greetings CNC fiends!

I originally posted this over on Geckodrive's forum but methinks it'll be answered more quickly here...


I acquired a G540 to replace the stepper controller in my desktop CNC mill (a Zenbot 1216, which at the time was only available with a Mechatronics controller) and will be using a Pololu 24v23 motor controller to drive a hefty 24VDC 15A motor as my spindle spinner. The Pololu board accepts a potentiometer input - or 0-3.3VDC into the potentiometer-wiper input, which basically acts as the input terminal to one of the on-board microcontroller's ADCs - as a control option. I noticed that the G540 has a 0-10VDC VFD output for spindle control. I'd love to have the G540 tell the motor controller what to do in response to Mach3's commands, as that'd neatly automate everything in my setup.


However, I have a couple questions on implementing this that I couldn't work out from the G540 manual, and thus far a search here hasn't helped:

Does the G540 emit 0-10VDC on the VFD OUT terminal or does it simply divide the voltage presented across the VFD +10VDC and VFD GROUND terminals? If it divides the voltage given from a supposed VFD, can it divide a 3.3VDC supply as well as it can a 10VDC?


If the G540 emits 0-10VDC I can use a multiturn potentiometer as an adjustable voltage divider to feed the motor controller, and if it can take the motor controller's 3.3VDC supply and divide that directly it's a "connect three wires and you're done" endeavor. Basically I just need to know which way I need to go with it.

Thanks in advance for any help you can give!



UPDATE: It appears that the motor controller has to provide the voltage for the G540 to divide, and the upper limit the G540 accepts for VFD+ is 12VDC. So, the question is now "can the G540 work with a 3.3-volt VFD source or does it have to be a higher voltage than that?"

[OddOne]

Replying to my own thread in case it helps, as I have found the answer...

Yes, the G540 can directly drive a Pololu 24v23 motor controller through the G540's VFD controls and the 24v23's 0-3.3VDC analog sampling control option.

What you do is tie the pot+ connection (which is 3.3VDC) on the 24v23 to the VFD+ terminal on the G540, the pot- connection (which is the power supply ground for the 24v23) to VFD-, and the pot wiper 1 slash analog-input 1 connection to VFD signal. Then, in the Pololu control and setup software, set the 24v23 to use analog input 1 and step through the configuration wizard while sending the G540 various spindle speeds as required so that the 24v23 will know what the G540 is asking it to do. I had to disable the 24v23's "safe startup" option since it wants a center-of-range signal as a "neutral" point (it's a bidirectional motor controller so you have forward/stop/reverse under normal conditions), and I had to check the "ignore pot disconnects" option since it appears the signal from the G540 is either intermittent (not likely) or a bit noisy and the 24v23 is very sensitive to noise (highly likely).

The only downside of this arrangement is that I'm not implementing bidirectional control - M3 and M4 both spin clockwise. But for what I'm doing I'm not really expecting to need CCW spindle rotation.

It's nice having a beefy 500-watt motor under Mach3/USB-SS/G540/24v23 control...