# HO coupler pressure sensor



## Shdwdrgn (Dec 23, 2014)

This may be a tall order in such limited space, but in the planning of a fully computer-controlled layout, one important aspect of switching is that the computer somehow know when your loco backs into a car. The best way I can think of to do this is by creating an analog pressure sensor on the loco's coupler.

An interesting aspect of the conductive foam used to ship IC chips is that when you squeeze it, the resistance across it changes. This has been used to make dirt-cheap pressure sensors for years (literally stick a wire through each side of the foam and measure the resistance). What I am envisioning is replacing the coupler screw with a pin that goes through the center of a small piece of foam. This would be enclosed in a custom coupler box, and the pin would slide in channels inside the box so that motion could be limited to forward/backwards (and limited to a maximum distance ). Then you have two wires coming out of the foam and going to an ADC.

If I'm thinking this through correctly, not only could you tell when you backed into something, but also when pulling a train down the mainline you might also be able to sense when an unexpected decoupling happens.

I wanted to put this idea out there to see if anyone had ever tried it before, or worked with the conductive foam as a sensor. Any thoughts on if this would be sensitive enough to 'feel' the change in weight of a single empty car? Any thoughts on other low-cost sensors that might do the job?


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## tjcruiser (Jan 10, 2010)

Check out Omega scientific instruments. They make (often cheap) strain gauges and piezo strips ... perhaps one to suit your needs.

www.omega.com

TJ


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## gunrunnerjohn (Nov 10, 2010)

Just put motion detection in the caboose, when it stops rolling, you know you've either stopped or something has uncoupled.


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## gregc (Apr 25, 2015)

there was a posting on another forum regarding braking of rolling stock, which got me thinking. i think the pressure/force due to coupling will be very difficult to detect with the foam and complicated both mechanically as well as electronically if an ADC is required.

i think a freely floating coupler gear box, a gear box that can slide slightly along the coupler axis, should be guaranteed to pull outward when pulling even a lightweight car. A phototransistor/led should be able to determine when the coupler has been pulled out, as well pushed in after coupling. (fiber light pipes may be less obtrusive). optical detection has no force cost. But building a floating gearbox is also a mechanical challenge. (A kadee #4 coupler may have been the answer).

since there may be situations when the coupler is already in the pushed in state, a very light weigh wire may be used to center the coupler. dual opto-detectors can then detect whether a coupler is pushed in during coupling or pulled-out when coupled.

now i'm curious about the force on a coupler when pulling/pushing a car.


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