7i76 Encoder wiring to BF20 RPM sensor - SOLVED

Hi. I have done a search and not seen this question so hopefully not doing a double post. If so any link to the appropriate thread would be appreciated.

The question: I have a BF20 mill. I would like to utilise (as a starting point) the hall effect sensor that already exists to sense the RPM. The existing wiring on the mill is essentially:

To be clear, the +5V/GND is provided by the BF20. I have seen references to other CNC systems (SimplexMotionHub) where they hook into the GND and the Signal from a BF20 and read the signal from there in Mach3.

What I am wondering is can I do a similar approach with the 7i76 Encoder pins? i.e. Wire the Encoder GND to the BF20 5V GND reference and wire a splice from Signal to the Encoder A+. I realise I would need to set the jumpers to TTL input and setup the count mode to 1 (True) in HAL (I believe Pnnconf has a switch for a single sensor).

The plan is to utilise the 0-10V (actually measured as 0-7.7V from spindle pot) and pull that reference voltage through the Spindle pins to have the 7i76 drive the voltage of its virtual POT to drive spindle speed. Add in the signal for RPM and linuxcnc should be able to drive the mill to a more accurate and consistent speed setting in an automated manner.

Appreciate any help and advice readers are able to be provide.

Cheers,
James.

its easter weekend so not many people here to answer
the GND bridge is right this gives the signal the way back to trigger

just look into halmeter if you got the signal clear by turning slowly with the hand
5V signals cand do electronic fails on the 7i76

Okay I kept researching and finally found some useful info on the wayback machine from a chap in Canada who tackled this problem and solved it. I used that as some inspiration.

The end solution was to not try and connect directly to the encoder but to create a very simple opto isolation board that triggers the encoder in TTL setting based off the signal coming from the hall effect sensor.

The basic structure for anyone interested is:

I have this working a treat and using it to run linuxcnc PID control over spindle speed. The next problem to tackle will be the on/off of the spindle. Just due to the way the control board works and tunes speed setting the virtual pot voltage to 0 does not stop the spindle. And reversing is a whole different kettle of fish. Which if I solve will I'll try and document for others to use.

Hopefully this might speed up someone doing the same thing.

Cheers,
James.

My old BF20L has a spindle driver with a "floating" pot... none of the ends is at ground. I traced the schematic a bit back when I also thought about speed control from linuxcnc, the pot is somewhere in an op amps feedback loop or similar (I don't remember, that was about 10 years ago). I do remember that the voltage was too high for most of the digital pots available then so I dropped the idea.
Reverse is made by physically changing the motor leads with a switch. Can be done easily with a relay but need to be sure that it's stopped first...

Maybe you have a newer machine/control and got it to work easier.