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GCA189 Magnet activated rail selector


By Peter Giling


Using sliding contacts have some negative results.
Most of all , in my experience, these contatcs are not full 100% reliable, which I do not like specially when I am showing a fiddle yard in public.
So a better solution was to be developed, and that better solution is coming in here.
A hallsensor like TLE4905 is capable of a maximum switch load of 100 mA at a maximum of 18 Volts.
So a relay like OmronG2R 12V , needing approx 50 mA is fine to be switched directly with it
The idea is to use this SPDT relay on each track-section and activate it with a fixed magnet .
In that case, there is zero friction, and the contact is 100% sure.
So I need a board for that.
I have 12 tracks on this Fiddle yard, so I need 12 relays in one line
And since I have 3 contact sections in each rail, I need 3 of these lines, with a total of 36 relays.
The easiest way to achieve that is to make a board with 4 relays, and fix 3 of them in a line.

Fortunately I have these 36 second-hand relays.
In any other situation, a well known Siemens relay with 3 or 4
DPDT contacts will do also, to use one relay for the three sections together.

This is my home made product.

On the top edge, 4 hallsensors are visible, with a distance of 40mm from each other, matching the rail distance on the slider.
The board is supplied by the rail power and a cheap 12 V regulator, and, for securety, also fused with 0,5A multifuse
With each relay there is also a led for easy indication and check.
Left and right are connectors for in/out of the railpower, and in the middle the connector for the 4 rail sections.

The GCA145 controller signals on J5 Pin 10 when Fiddle yard is in position.
The output is active when at 0V.
This signal is also used to switch all railpower to the rails on the sledge, making it impossible for trains to run while the fiddle yard is moving.
Relay board GCA189-b is made to match perfectly this signal.
The board is also has option to use it with positive signals.

to be continued............

The hardware files



gca189-en.txt · Last modified: 2019/10/20 20:24 by phg