Raspberry Pi 4 with Mesa 7c81

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22 Apr 2020 05:41 #165045 by helioz2000
As a newcomer to LinuxCNC and Mesa products I struggled to get may head around the 7C81 interface card and how it all fits together. Maybe the images below will help the someone to get a clearer understanding of the 7C81 and how it all fist together.






The images show a Raspberry Pi 4 mounted on to 7C81, a home made 40pin jumper cable and a DIN rail mount made up from the following Phoenix Contact products purchased from RS parts:
804-7549
804-7546
804-7420

I will provide more photos once I have 7C81 + 7i85S mounted in the switchboard.
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The following user(s) said Thank You: tommylight

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22 Apr 2020 06:46 #165050 by rodw
Replied by rodw on topic Raspberry Pi 4 with Mesa 7c81
Looks neat. I wonder if you could mount a PoE hat on top of that for the ultimate compact no wires setup? I've got a couple here with PoE and they are nice and compact.

Its nice to have those part numbers. Can you clarify that the base 804-7420 comes in 1 metre long lengths?

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22 Apr 2020 12:09 #165085 by tommylight
Very neat. :)

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22 Apr 2020 23:26 #165164 by helioz2000

rodw wrote: I wonder if you could mount a PoE hat on top of that for the ultimate compact no wires setup?
Can you clarify that the base 804-7420 comes in 1 metre long lengths?


1) There is sufficient space for a PoE hat, but I'm not sure that it's needed as the 40pin jumper provides the Pi with 5V power from the 7C81. The 3rd photo shows the 5V connector on the 7C81 which has good current carrying capacity and is more than adequate to power the Pi and the 7C81 + IO modules. I measured power consumption of my setup (7C81+7i85S) at around 1.2A with peaks of 1.5A, but that's without encoders and only one stepper drive connected.
I'm not sure that powering the 7C81 from the Pi via PoE hat is a good option, particularly if the 7C81 is jumpered to provide power to a few other IO modules, as all current for the 7C81+Anything IO modules would have to go through the 40pin jumper.

2) Yes, the UM108 rail comes in 1mt length and needs to be cut to size, but I'm sure it will come in handy for other projects. The hint for this came from page 1 of the 7C81 manual: ".. mounts in standard 107mm DIN rail channels". You can also find the UM 107 profile on AliExpress, but shipping from China is an issue at the moment.

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23 Apr 2020 01:18 #165171 by rodw
Replied by rodw on topic Raspberry Pi 4 with Mesa 7c81
Thanks for clarifying those points. I as not aware of the builtin power so PoE is not required...

I found the listing and saw the end caps were only $1.40 and then the backing was $56 and I nearly had a heart attack...

helioz2000 wrote: You can also find the UM 107 profile on AliExpress, but shipping from China is an issue at the moment.


Tell me about it. Today's job is to get 100kg of custom made parts out of China. The freight price is very keen...

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26 Apr 2020 22:16 #165709 by cakeslob
that looks pretty clean in the din rain mount. can you post a more in detail shot of your stand offs on the ribbon cable side? I have been curious as to how others do theirs

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27 Apr 2020 01:16 #165732 by helioz2000

cakeslob wrote: that looks pretty clean in the din rain mount. can you post a more in detail shot of your stand offs on the ribbon cable side? I have been curious as to how others do theirs


Ah yes, that part is bit tricky. It's actually not a full stand off, just a plastic M3 bolt with nuts, took a little bit of effort to get that arrangement into position. It's now installed on a gear tray, so no longer that easy to see .... I will try and take some photos for you tonight.

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27 Apr 2020 11:51 - 27 Apr 2020 13:08 #165804 by helioz2000

cakeslob wrote: .... can you post a more in detail shot of your stand offs on the ribbon cable side?

Here is the detail you requested:

The bolt coming up from the underside is tightened with the clear nut against the top of the 40 pin connector, a second [black] nut locks the clear nut into place and provides the correct height to match up with the standoffs on the other side. It tends to want to slide off the side of the connector until the pi keeps the two bolts at the correct spacing.
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Last edit: 27 Apr 2020 13:08 by helioz2000. Reason: added more information

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21 Oct 2020 14:57 #186814 by merlinfive
Hi , I'm thinking of doing something similar just ordered a PI4 8GB , how about your progress , already finished ?

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21 Oct 2020 18:08 #186830 by rkh
Replied by rkh on topic Raspberry Pi 4 with Mesa 7c81
I'm also going to be giving this a shot. Does anyone know more about options for breakout boards? I wasn't feeling too confident about the generic Mach3 BOBs I saw, so I've got a C10 from CNC4PC on the way - hoping this would work but not sure if things will need to be remapped at all or not. I also saw Mesa has the 7i78, but that's not specifically listed in the 7c81's support archive. Anyone know if I could expect that board to work OK?

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