7i76e available input types vs mode

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09 Nov 2018 15:00 #120332 by Nitram
Hi Peter.

The 7i76e has 3 modes, i.e. 0 = I/O, 1 = I/O + analogue and 2 = I/O + analogue + encoders.

I use the 7i76e in mode 1 with 4 analogue inputs. I do not use any encoders on the board.
I have need for one more analogue input. If the board is being run in mode 1, does this open the 4 inputs on the other TB for analogue input as well? I.e. those that would otherwise have been used for encoder input in mode 2?

If not, is there any Mesa flash available to facilitate this?

Thanks,
Marty.

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09 Nov 2018 16:15 #120334 by PCW
No, currently 4 analog inputs is the maximum

Its possible hardware wise but would require a new mode added to the 7I76 portion of the 7I76E

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09 Nov 2018 17:28 #120337 by andypugh
One possibility if the analogue inputs do not need to be sampled quickly would be to multiplex the analogue inputs.

This would need to be done in hardware.

uk.rs-online.com/web/p/zener-diodes/1707984/

Is an example of something that might work.

linuxcnc.org/docs/devel/html/man/man9/demux.9.html

Could divert the values to different HAL pins. Then a simple counter to cycle through the two selection bits in both hardware and software.

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09 Nov 2018 19:42 #120347 by PCW
I do have a Delta-Sigma A-D hm2 module that can make a pretty decent 10 or so bit 1 KHz A-D from a LVDS FPGA input pair but it requires 3 I/O bits per A-D (1 out and the LVDS pair used as a comparator) and 2 Rs and a C per channel (so you could get 5 A-Ds from a 17 I/O 7I76E expansion channel)

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09 Nov 2018 20:05 #120349 by Nitram
Hi Andy.
The purpose of using the extra analogue input was to get VFD frequency feedback (as pseudo motor speed feedback) to explore your Automatic spindle gear detection on my lathe.
Do you have any thoughts as to whether there is a better or easier way without an analogue input to monitor this parameter for this purpose?
Thanks,
Marty.

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09 Nov 2018 20:32 #120351 by andypugh
Can you control the VFD via Modbus?

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09 Nov 2018 21:17 #120352 by Nitram
I have all the serial ports available on a 7i85 which is connected to the 7i76e and is only utilizing encoder inputs. So physically it is possible st that end. I'll have to check the drive is capable. I have a hy drive so will check.
Is much involved in setting up of the modbus? I'm afraid I know little about it...

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09 Nov 2018 21:37 #120353 by Todd Zuercher
It is simpler to connect directly to the PC via an inexpencive USB dongle. No one has ever written a Modbus driver for Mesa hardware. While theoretically possible, I'm told it would have to be written into the firmware for the FPGA or the Hostmot2 driver or both, and that is easier said than done. (I really have no idea and it is well beyond my capabilities.)

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09 Nov 2018 21:55 #120356 by Nitram
I saw this but do not know how relevant it is...

linuxcnc.org/docs/html/drivers/mb2hal.html

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09 Nov 2018 22:02 #120357 by andypugh

No one has ever written a Modbus driver for Mesa hardware. While theoretically possible, I'm told it would have to be written into the firmware for the FPGA or the Hostmot2 driver or both, and that is easier said than done.


It's on my list. But not at the top.

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