7i76 analog spindle power options

Trying to wrap my head around what to use to power the analog spindle control of the 7i76. I am running a KBMM-225D which states it needs 0-9VDC. All seems simple enough but I get hung up on two things.
1. The isolated power supply portion
2. Whether I can use a 12v source and somehow limit the output via software to the 9v required.

Here are my current power source options:

12v from the computer power supply, I have a 450w that is only running an Intel D525 board and a fan

A generic 12v 120w switching power supply, has two terminals, only one of which is used to run a 1amp oil pump and some switches and relays for other things such as coolant pumps

A wall wart that is probably older than I am that I have lying around, 12v 400ma

I already have a large number of items plugged into the same AC plug including a 48v switching supply, spindle motor itself, 24v power supply for the 7i76 and all but the wall wart mentioned above. Instinct tells me the wall wart is the way to go but I would love to avoid one more item plugged in to the power strip. I am not very electrically inclined however.

Thank you in advance for the help and advice.

Regarding #2, it can actually be quite simple using a resistive voltage divider.

en.wikipedia.org/wiki/Voltage_divider

The only thing you need to be careful about is that the current through the two resistors isn't excessively high for the output, and that there's enough current to drive your input - which shouldn't require much at all.

Play with it on a bench with a potentiometer hooked up to your 12V supply and you'll see how the circuit limits the output. You can also check the current through it this way if the calculations elude you.

Thank you for confirming that I once again way over thought this. I got caught up trying to follow an example I found on the mailing list.

So I will run TB4:
1 Spin- to P1
2 Spinout to P2
3 Spin + to P3

Will also be running the Spinena in place of a safety shield switch that I believe needs to be NC to run. But that is for another day. Thank you for the help.

This isn't working. I connected as I had planned and am only getting half my spindle rpm. The spindle out is only 4.8v at max and 5ma. I believe it's over 7v on spin+ when it's not powered on. Kbmm works fine with a potimeter connected and if I recall was pulling around 10ma at 9v full speed. Kind of at a loss at this point as everything I have read has to do with using this board with a VFD.

As a follow up. I replaced the power source. Instead of running from the kbmm board I used a 12v wall wort. I now get close to max speed but the spindle out will only give 8v. And spindle rpm does not scale well at all. The kbmm can use 0-9v set up with an outside power source just need to figure out how to get the last volt. At current max setting spin+ still has 12v so there is more power to have.

I found it interesting that in pncconf the max voltage could only be set to 10v even though the manual says the 7i76 can use 5-15v. Anyway to increase this voltage.

To fix the rpm scale issue I was thinking to use a c3 pulse index card wired into the encoder slots on the 7i76. The current perforated rpm ring I have has 12(?) holes. Is a 12 count encoder enough for Linux to do read the rpm and get more accurate spindle speeds?

The spindle output of the 7I76 should be 12V with a
full scale command if the spindle power is 12V

That is if hm2_5i25.0.7i76.0.0.spinout = hm2_7i76e.0.7i76.0.0.spinout-scalemax
and hm2_7i76e.0.7i76.0.0.spinout-maxlim does not limit hm2_5i25.0.7i76.0.0.spinout
then the output should equal the power supply. If this is not the case something
is wrong and needs to be investigated

I can check that on tuesday when I get off work. While I have your attention I would like to verify the setup for linux to read the spindle rpm.

Using a c3 pulse index card (or if there was a way to pull the signal from the existing G0704 tach that would be even better) and a 12 hole disk. I would bring the TTL signal into ENCA+, ENCB+ and IDX+( do I need to bring the single line to 1 or all 3? I wont have an index.) with jumpers W4,5,6 in the left hand position. Once I go through pncconf and set it up for encoder I am assuming that would generate the necessary HAL components.

With this setup will linux adjust voltage output through the the 7i76 to acheive the desired RPM. I did find this info and have read it wiki.linuxcnc.org/cgi-bin/wiki.pl?Closed...pindle_Speed_Control
Understanding HAL so far is beyond me.

Thank you for the help.

Found this regarding the KB boards and how they operate:

"Making a long story short, referencing page 5 of the Soigeneris document (thanks Soigeneris) the MIN speed potentiometer on the board raises P1 above F-; and I'd hazard a bet that the MAX speed potentiometer lowers P3 from F+. The MIN, Speed, and MAX potentiometers are in series and thus make a voltage divider circuit; the resistance of the 7i76 board's "replacement" is different, but measuring while tweaking would bring the voltage across the 7i76 to 7v, which is what is required in voltage follower mode on the KBIC controller. (and, of course, V- and F- are the same, and, I'd bet that V+ and F+ are also the same, but I have not measured it)"

As it relates to my issue I have voltage following mode wired + to P2 and - to P1 so I am most likely not refernicing ground properly and thus only out putting the 8v instead of 12v. Will post again if this resolves the issue.