Omron proximity switches producing unexpected voltage step down

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29 Sep 2022 16:31 - 29 Sep 2022 16:39 #253034 by JJ48_24
Hello. While switching the controller on my Chinese router over to linux cnc I ran into an issue with the limit switch. The limit switches are given 24v at the controller but only output 12.6v. Unfortunately the threshold for activating an input on the 7i76 is 60% voltage. The limit switches I am using omron tl-q5mc1 switches. I looked through the data sheet but found no mention of any kind of voltage step down. I have thought of using a buck boost converter or using analog inputs on the 7i76 however these both feel both feel like inelegant solutions. I feel like I have to be missing something. Am I missing something in the switches datasheet, and is there anything else I should check?
Last edit: 29 Sep 2022 16:39 by JJ48_24.

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29 Sep 2022 18:45 #253042 by PCW
Those are NPN type proximity switches

You can connect PNP type proximity switches directly to 7I76 inputs,
but NPN type switches require an external pullup resistor.
(suggest 2K 1/2W for 24V)
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29 Sep 2022 21:44 - 29 Sep 2022 22:19 #253056 by andypugh
To elaborate on what PCW has said, if you are treating them as a voltage output then you are using them wrong, you should see them as a switch. PNP is a switch-to-live and NPN is a switch-to-gnd.

In some ways NPN are more flexible as you can power them with 24V but use them to switch a 5V input
Last edit: 29 Sep 2022 22:19 by andypugh.
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29 Sep 2022 22:10 #253058 by tommylight


In some ways NPN are more flexible as you can power them with 24V but use them to switch a 5V output.

You should see how people look at me all funny when i tell them that! :)
Also, "5V input"?

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29 Sep 2022 22:19 #253060 by andypugh

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29 Sep 2022 23:04 #253064 by JJ48_24
I see. The one thing I am confused about is why am I getting 12v on the logic pin. If they are switches to ground shouldn't I be getting 0 as the 7i76 is a sinking board? Got the resisters ordered on amazon and they are coming tomorrow.

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29 Sep 2022 23:26 - 29 Sep 2022 23:27 #253066 by PCW
Some NPN sensor outputsĀ  have weak pullups to their power input
Last edit: 29 Sep 2022 23:27 by PCW.

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