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GCA179 Isolated Hall-sensor and/or reed-switch input unit.


By Peter Giling


The use of Reed-Switches is fairly common in garden railroad environment.
It is cheap but face a few problems.
First there is the 'contact dender', causing multiple contacts in one switch action.
Rocrail does not have any problem with that, as long as it is just a simple feed-back.
But using the switch as a wheel-counter (or magnet counter here) would give some problems.
And specially this wheel counter is a very nice option, so far hardly anywhere available but in Rocrail it is standard.
Second there is the fact that the contact given by a passing magnet is a rather short pulse.
Most units in LocoNet or CANBUS useually need a pulse-length of minimal 50-75 milliSec.
And the third fact is that reed-switches have a short functional life, when incorrect current is switched, either much too high or far too low.
The last issue can be improved by switching the correct current as given by the specifications of the reed-switch, which might be mostly very hard to find.

For all three problems, there will be one simple solution.
At the present moment I am finishing the development of GCA179 buffer board.
It has 8 isolated inputs, useable for reed-switch and/or hall-sensor. where a for the reed-switch 'healthy' current of approx. 50 milliAmp will be possible.
The hall-sensor does not have any problem with that current.
The isolated input enables the use of common Railpower wiring for the reed-switches, which makes it possible to use any existing wiring.
This GCA179 has a connection to GCA50 / CAN-GC2 / GCA_PI02 which also provide the 5V supply for the on-board processor.
This processor will extend a minimal pulse length in each input to a 0.1 Sec pulse for GCA50/CAN-GC2/GCA_PI02.
At the same time, this longer pulse will sufficiently suppress the multi pulses from contact dender of a reed-switch.
Hall sensors do not provide contact dender at all, in popular expression: one magnet is one pulse.


  • 8 inputs with opto-couplers.
  • minimum pulse length to activate output = 1 mSec.
  • output pulse length standard 100 mSec minimal.
  • separate 12 Volt 200 mA (100 mA for hall-sensors only) needed for sensor circuit
  • two types of connector possible for 8 inputs : RJ10 or 2/3 terminal screw.
  • up to 100 mtr wiring from sensor to GCA179 possible.

The prototype

A working prototype is already a fact… And the final board has already arrived…
The complete board with RJ10 sockets
for hallsensor connection
This board shows the option for using 2 Way screw-terminal (hall7 reed switch)
or 3 way screw-terminal (hall 8 hallsensor)
All hallsensor connections have this same option.
= = = = used screwterminals for hall/reed connections are 3,81mm/0,15'' pitch types = = = =


Connection HallSensor or Reed-Switch to GCA179


gca179-en.txt · Last modified: 2018/11/12 08:56 by