My Kingdom For a Schematic

You never know how handy a schematic is until you are without one. I tried various ways of enabling and controlling the spindle without success. Part of it was confusion with EMC however most of it was because I was unsure of the layout of the encoder board.

I knew that it boiled down to the signals being presented to the Enable and Vtrip input pins on on the Spindle control board. Enable needed to be held high and the voltage at Vtrip would control the speed of the spindle. I proved that to myself by removing the encoder board and hot wiring the Spindle card directly with the needed signals.

Still, I could not get the spindle to spin up with the encoder board in the machine. Finally I decided to take the time to trace out the circuit on the encoder card. It took a while, 4 opamps, 5 transistors and quite a few discretes on a double sided board can get fairly confusing. I just took it slowly worked on it a bit each evening and eventually came up with this.

Once the mysteries were revealed it was obvious that the control signals where going to have to be repetitive square waves as all the inputs ultimately go through a cap before they can induce voltage on Vtrip. Looks like there is some kind of feedback from the S1 and S2 encoder signals on the spindle itself too, so I am guessing once you set a speed it will maintain even if you encounter a load, this is good news if its true.

In the end I just removed the clamshell from the parallel port cable I was using. Removed all but the signal wires for the XYZ axis, then routed Pin1 from computer to Pin11 of the machine port. Added that control pin to my config file using stepconf, and joy oh joy. I now have control of the spindle from the computer.

Next step is air, the spindle collet opens and closes with air pressure, looks like it may finally be time to get a small compressor for the shop. 😉


One Response to “My Kingdom For a Schematic”

  1. Tim says:

    Interesting! I’m also retrofitting a pair of old Ozo model 18s with EMC2, for general routing and perhaps eventual use as a “repstrap” (3d printer) and pick-n-place system. I found your blog looking for a schematic of the driver card to see how the frequency input and hall-effect feedback interact to drive the spindle. Your description and schematic of the control logic answer my most important question though: the ultimate result is an analog voltage after all (the frequency input does not directly pump the transistors on the driver card), so alternate waveforms such as PWM/PDM or stepgen steps can work. I was worried that deviating from the 50% duty cycle squarewave input would potentially blow the driver board.

    Looks like yours is pretty well working already, but if you’re interested, I have scans (well…photos) of an original 18/24 manual complete with wiring diagrams and (some) schematics I could email.


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