One more HURCO BMC 20P Retrofit

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21 Aug 2022 23:44 #250175 by rodw
The picture looks like they have used a normal 25 pin DB25 to connect to a break out terminal board. I would expect 7 & 10 would be +24v and -24V.
If thats the case, half the pins may be commoned internally and the other half will be used for the limit switch signals. Eg say your pin 2 (or 16) would be commoned to 7 or 10.

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22 Aug 2022 09:41 - 22 Aug 2022 09:42 #250193 by christos
As always thanks for everyone’s input.

Things were simpler than initially thought…
Basically the limit switches have three contacts, one for power (com), one for normally open and one for normally close. My idea is to use them as NO, give them 24V and return the pins (the signal) to the inputs of 7i77.
My query remains though, giving them “unlimited” 24V (just connect them to the PSU) and expect to return back to the 7i77, am I in danger of smoking the card?
Is there a limit of how much voltage/current the 7i77 can accept on inputs?How it’s usually done?  Is it ok, to send 24V from the 7i77 (from an output but it will be always on) and get the signal back to one of the inputs?
Last edit: 22 Aug 2022 09:42 by christos.

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22 Aug 2022 19:51 #250225 by arvidb

Is it ok, to send 24V from the 7i77 (from an output but it will be always on) and get the signal back to one of the inputs?

Yes. From the 7i77 manual, the inputs have a nominal 20 kΩ input impedance (well, technically the manual says 20 kelvin-ohms, but I think it's obvious what is meant. :)). I cannot find anything in the manual about maximum current (and therefore voltage) that the inputs can handle, but the manual gives several examples of using them with 24 V.

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22 Aug 2022 19:58 #250226 by PCW
Replied by PCW on topic One more HURCO BMC 20P Retrofit
You can connect directly from a 24V power supply to 7I77 inputs
(the 7I77 inputs will take -36V to +36V indefinitely)

If you have a high current 24V supply you should fuse appropriately
to protect the wiring in the event of a short.
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22 Aug 2022 21:54 #250232 by tommylight
Example, roughly:
24V/20KOhm = 24/20000=0.0012A
That is 1.2mA, so no matter how much amps the power supply can put out, it will be the maximum an input will use.
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26 Aug 2022 06:33 - 26 Aug 2022 06:34 #250489 by christos
Hey guys!
Thanks for putting up with me.

As my level of electronics is obviously lower than the one needed to get everything wired up fast, I decided to start a wiring diagram so I could evaluate all connections beforehand. I will share it with you when it comes to a “readable” state.

Now, I have a different question. As you have noticed correctly, the 7i77 has a 20kΩ input resistance, but when I have checked the resistance using a digital multimeter, I’m getting a different result (with no power anywhere).

Attached a photo, why am I getting 10.9kΩ? Do I have a different version of a 7i77?
 
Attachments:
Last edit: 26 Aug 2022 06:34 by christos.

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26 Aug 2022 09:19 - 26 Aug 2022 09:21 #250498 by tommylight

From the 7i77 manual, the inputs have a nominal 20 kΩ input impedance


Impedance and resistance are not the same thing, although pretty close.
So 11Kohm would be roughy 2.5mA or 0.0025A.
Short explanation, impedance is resistance that changes depending on voltage or current, so it is used for inductive loads, like speakers.
Last edit: 26 Aug 2022 09:21 by tommylight.
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26 Aug 2022 12:37 #250508 by smc.collins
id6 not be worried about it the difference between 11k and 20k in terms of current is inconsequential amd maybe be a result of your meter not being accurate. many meters are not accurate. if you are measuring resistance check from the 7i77 ground terminal on the tb connectors to your input.
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27 Aug 2022 09:29 #250565 by arvidb

Attached a photo, why am I getting 10.9kΩ? Do I have a different version of a 7i77?

You cannot measure resistance of semiconductor circuitry like that. The DMM applies a small, known current between its test leads, measures the resulting voltage, and calculates the resistance using Ohm's law (U=R*I). This only works with purely resistive elements, not with semiconductor parts. The result will be nonsense - for example, you are likely to get a different value by simply switching the test leads around.
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12 Feb 2023 15:18 - 12 Feb 2023 15:20 #264356 by christos
Hello guys

After a couple months of inactivity due to personal issues we are back with a bigger appetite to complete this project. It has been quite a steep learning curve for me (linux, linuxcnc, electronics) but we are slowly getting there.

After all encoder feedback is connected, and while in the process of connecting the Yaskawa servopacks to the 7i77, I have a query regarding the pncconf wizard.In the pncconf wizard, I think I was missing the correct firmware so the 7i92 can properly display the connections between itself and the two mesa cards connected to it, the 7i77 and the 7i74.

I have found the firmware (7i92_7i77_7i74D.bit) downloaded and successfully (I think) loaded it. But when I’m opening to create a new pncconf wizard I still do not get the option of the firmware I have installed. What I’m doing wrong here? Is there another way to do it rather the command:

mesaflash --device 7I92 --addr 10.10.10.10 --write 7i92_7i77_7i74D.bit
Last edit: 12 Feb 2023 15:20 by christos. Reason: format all messed up

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