Using RC pins for simple NC limit switch


I have an SMC G2 18v15 that has been opening and closing my telescope observatory roof for some time now. All has been well until recently.

I’ve been using Analog 1 and 2 for roof open/close limits, employing NC limit switches. A2 has stopped functioning, and always reads invalid channel now.

I can, of course, replace with another controller, but I’d like to avoid the cost (and frankly the wait…should have clear skies in 2 days! lol ).

I’m making no use of any of the RC pins. Docs say I can put them to use as limit switches, and I could easily change my code to read their status, but I can’t for the life of me figure out how to wire it up!

I’ve been using the Internal pullup diagram shared at Pololu - 4.6. Connecting a potentiometer or analog joystick for the analog switches, which works fine…but no similar diagram is included in the docs for using an RC channel.

So, newb question I know, but can anyone simply tell me how to wire up a simple NC switch to the RC channel 2 pins to act as a limit switch?

Thanks in advance!


While the RC input pins can be used as limit switches, they still expect an RC signal input (e.g. you can use it as a kill switch from an RC transmitter/receiver), so a simple pull-up and momentary switch will not work.

Do you know what happened that caused the A2 pin to stop functioning? There are 3 different “invalid” statuses for the analog inputs: invalid (disconnected), invalid signal, invalid (too high), and invalid (too low). Which specific invalid message are you seeing? Also, could you post a copy of your settings file? You can save a copy of your settings file from the “File” drop-down menu of the Simple Motor Control Center G2 software while the controller is connected.


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The A2 simply lost a pin I’m guessing. It’s always “Switch Active” (trained for a NC switch). I’ve doublechecked to make sure the switch circuit itself is fine (it is), and done bench testing with known good switches. Indeed, a switch that works fine on A1 simply returns “Switch active” on A2 in any position, so pretty confident it’s simply dead.

No, I don’t know why…but this unit is several years old, and spends its entire life “outdoors”. (In an observatory, yes, but subject to all temps of the year, humidity, etc). My guess is…it simply gave up the ghost. I can’t really blame it. lol

Settings file would probably be not terribly useful now, as I’ve changed quite a few things, both in an attempt to make RC work as a limit (which i now see can’t be done), fiddling with the Analog inputs, and finally adjusting things for “manual” open/close for a few days while I wait on another unit to arrive. :slight_smile:

No worries here. “It doesn’t work like that” is a fine answer for now, and I’ve another on the way, so all good. :slight_smile: Thanks for the time and response!

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