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Searching for block occupancy detectors

Postby dvdouden » Fri Feb 02, 2018 11:11 pm

Been playing with the idea of adding block occupancy detectors to my future layout. Got a few hall effect sensors; they detect magnetic fields and I was hoping I could stick some under the track and that they would be able to notice a passing train. Unfortunately the signal is so weak that the noise on the power line has more effect on the signal than the passing train :roll:
It would've been ideal if this had worked; they're fit nicely in the track bed, are just a few millimeters in size and cost about 11 cents each.

Option two: infrared. Drilled a hole in a piece of track and put a sensor module underneath the track with the actual sensors poking through the hole. This seems to work a lot better:

Not too happy about the hole in the track, but perhaps this is less visible when using flex track.
These modules cost about 30 cents each, the sensor itself about 9 cents.

Anyone got other any alternatives or experience with this in T gauge?
My T-gauge stuff on github: https://github.com/dvdouden/tgauge
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Re: Searching for block occupancy detectors

Postby dkightley » Sat Feb 03, 2018 12:39 am

I have LDRs as sensors on The Bridge. They use ambient light.....well more like the LED floods used above the layout......as a light source, and with the LDR mounted immediately under a slightly opened up gap between sleepers in the flexitrack, they're pretty reliable in operation. Here's probably the only photos I have showing what the fitted sensor looks like: viewtopic.php?f=8&t=123&start=353

The only slight issue is the very occasional false triggering of the sensor by wayward visitor's arms/hands pointing to things on the layout.

For the DCC system on The Bridges at Saltash, I'm using a more substantial LDR sensor system as described here: viewtopic.php?f=10&t=525&start=11 As all bar one of the sensors will be behind the scenes, I'm fitting a small arch over the track with an LED shining down onto the track.....with the sensor LDR underneath. The LDR is part of a simple transistor switch putting high/low voltage on a CBUS multi-input module. If you read that thread further, you'll see I'm also using detector circuits that sense if a DCC decoder is present across a section of track.
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Webmaster here and volunteer at the National Tramway Museum http://www.tramway.co.uk
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