Author Topic: Is there any problem running a NO button long distances?  (Read 146 times)

HeneryH

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Is there any problem running a NO button long distances?
« on: December 11, 2018, 12:54:05 PM »
My Gateway/Moteino system to control an entrance gate lock is coming along nicely.  I'm basically replacing an off the shelf keypad system with the Mote system.

One item remaining open is the "exit" button on the inside of the gate that people press to unlock the gate so they can exit.

Now, sure, I get it, I can put a Mote at that exit button location but I'm starting to run out of Motes!

I already have wires running there for the existing exit button...

Is there any danger in running a NO button to the Mote system to accept exit requests a longer distance?  On the breadboard, it is just a simple press button into a D input using the internal pull-up resistor.  Pressing to ground initiates the event.  What if I were to locate that button 100 feet away for instance??  Is the extra capacitance of the wire run going to cause problems?  Anyone have any experience with this?

Felix

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Re: Is there any problem running a NO button long distances?
« Reply #1 on: December 11, 2018, 01:05:32 PM »
I would not run it more than a few feet, with some really good wire.
More than that, and especially exposed, it can invite transients and pickup all kinds of noise into your Mote, something you don't want.
Plus, do you really want a button wired to 2 x 100ft pieces of wire? That sounds like way more aggravation than the cost of a Mote  :'(

HeneryH

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Re: Is there any problem running a NO button long distances?
« Reply #2 on: December 11, 2018, 01:19:00 PM »
The current button is already wired 50 feet to the keypad, I would just use existing spare wires to extend that back to the Gateway another 50 ft.

I already knew the answer before I asked.

Maybe I'll use the existing wire to send 5v to the location for another Mote and send a wireless button-press event back to the gateway. 

TomWS

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Re: Is there any problem running a NO button long distances?
« Reply #3 on: December 11, 2018, 01:28:47 PM »
I would be more concerned about static electricity into a sensitive circuit like a Mote.  In this case, as I have done with an outside rain gauge, I'd connect the contacts via an optoisolator.  In the rain gauge case I actually have a separate battery pack (2xAA) to supply an isolated power to the switch side of the isolator and then the output side of the isolator goes into the Mote.  It works well and the batteries last for their shelf life.

You could run the wires hundreds of feet in this case.  However, then Felix's concerns become more relevant, but adding low pass filtering and Debounce SW to the Mote solves that issue.

Tom

HeneryH

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Re: Is there any problem running a NO button long distances?
« Reply #4 on: December 11, 2018, 03:54:46 PM »
Do LiPo batteries (or others for that matter) have freezing temperature problems that I read about somewhere here in a time long ago?

TomWS

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Re: Is there any problem running a NO button long distances?
« Reply #5 on: December 11, 2018, 04:21:49 PM »
Do LiPo batteries (or others for that matter) have freezing temperature problems that I read about somewhere here in a time long ago?
Manufacturer specification for common LiPo batteries is:
Discharge Temp Min/Max: -20C/60C
Storage Temp Min/Max:  -20C/25C (1Year), -20C/40C (3Months)
Battery Life will be affected to some degree when discharging at the limits

Felix

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Re: Is there any problem running a NO button long distances?
« Reply #6 on: December 11, 2018, 04:50:40 PM »
Manufacturer specification for common LiPo batteries is:
Discharge Temp Min/Max: -20C/60C
Storage Temp Min/Max:  -20C/25C (1Year), -20C/40C (3Months)
Battery Life will be affected to some degree when discharging at the limits

I never was able to find any such specs on chinese LiPos I bought either from aliexpress/ebay or adafruit/sparkfun. I believe the reason is that they are low quality get-what-you-pay-for.

Here's what "common" means to the average DIYer:

From adafruit 500mAh lipo:

Weight: 10.5g
Size: 29mm x 36mm x 4.75mm / 1.15" x 1.4" x 0.19"
Power Lead Length: 80mm / 3"
Output: 500mAh at 3.7V nominal​

No electrical or temp specs (3.7v is not a spec and XYZmAh is usually a lie - they are less than claimed :D).