5v limit switch on 24v powered mesa 7i76e

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23 Jul 2019 16:46 #140314 by bdepalle
Hi everyone,

I am faily new to the cnc world and I am building a small 3-axis mill using stages that are built with optical switches (Optek OPB960N51). The switches are limited to 5v and my 7i76e control board is setup to run at 24v. So I am trying to figure out what is the best option get these switches to work with my setup.

From the various info I have gathered, I have few options:

1. Set the I/O voltage of the 7I76e to 5V which I would rather not do as I have other sensors running at 24v.

2. Use encoder inputs since they give 5V inputs readable on the encoder A,B, and Index pins. Though I have 6 limit switches and there is only 1 encoders on the 7i76e so I am short of 1 spare encoder.

3. Add another board powered with 5v specifically for my limit switches. Do you have any suggestion for this?

4. What about using a voltage converter/optocoupler. I have seen this mentioned a couple of time but never discussed. Is there any reason not to do this? Can there be some issues with reliability?

Thanks,

Baptiste

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23 Jul 2019 17:11 - 23 Jul 2019 17:13 #140316 by PCW
1. You can connect 5V signals directly to the 7I76Es expansion ports, _but_ if
you mis-connect these pins you might damage the FPGA, or bus switches.

2. You could use a cheap parallel port breakout like the CNC4PC C10 connected to one
of the 7I76E's expansion ports to give you at least 13x 5V inputs and protect the 7I76E

3. You could use a Mesa 7I74, 7I85, 7I85S, or 7I89 (connected to a 7I76E expansion port)
to get more 5V inputs
Last edit: 23 Jul 2019 17:13 by PCW.
The following user(s) said Thank You: bdepalle

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01 Aug 2019 16:54 #141126 by bdepalle
Thanks Peter for the clarification.

If I want to go with a CNC4PC parallel port BOB, am I correct in assuming that I will need to use an dedicated .bit file?
Does the 7i76e_JUSTIO.bit file is the way to go?

Thanks,

Baptiste

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01 Aug 2019 22:33 - 01 Aug 2019 22:36 #141157 by PCW
No need to change bitfiles, unless you want additional step/dir etc on the BOB

Forgot to say that you could also use a 7I75 on either of he 7I76E expansion connectors
That would give you 17 inputs or 17 outputs or any mix ( the 7I75 is a passive FPGA I/O protector/breakout board )
Last edit: 01 Aug 2019 22:36 by PCW.

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02 Aug 2019 06:17 #141173 by pl7i92
why not simply using a 1USD Arduino Relay board to get the switch working
there are also up to 8block arduino raspberry relais 5or 12V

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