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GCA94 8 Input power efficient current detector, also suitable for high current G and 1 Track.


By Richard Andrews, Helmut Schäfer and Peter Giling


The current detector GCA93 is a reliable way to creatie feed-back in your layout.
But many railroaders experience the 1,2 Volt loss of power as not appreciable.
And also, the current is limited to the maximum load of the bridge rectifiers on the input side of GCA93.
That will basicly disable the use of GCA93 with G-track or 1-track railroaders.
So we created a better solution.
Richard Andrews had this same thought and has been experimenting with different options by using a current tranformer more or less directly connected to A/D converter.
In that way, without any form of amplification, it is hard to reach the minimal 2,6 Volt, you need to activate an input suitable to be used straight to digital systems.
It was fearly easy to add an amplificator to it, but that also increased the sensitivity to distorsions.
In Germany, Helmut Schäfer created a different approach, using two transistors of which the first one is in normal conducting state.
This eliminates the sensitivity to distorsion, as always produced by running trains. sells this board in two or four ports.
This superb design of Helmut Schäfer is permitted to be used for the GCA94.
GCA94 is made to accept 8 inputs, and can be used like GCA93, straight to GCA50, CAN-GC2, GCA_PI02 and WIO.
No measureable power loss is the result, and there is no need to protect each input with a multifuse, like on GCA93.
The unit is functional compatible with GCA93, also each input has its own indicator led.
One of the two wires to the rails is feeded through any of the coils, which will mostly be sufficient for any locomotive or illuminated waggons
For more sensitivity, a second or third loop through the coil is possible, which could be necessary when you like to detect also
10K resistors, mounted between the two wheels of a waggon.
One other and better way to increase the sensitifity is to feed both rail wires through the coil, but in opposite directions.
Note: This unit is strictly made for ac, because it uses a current transformer.
So any digital system (which is also ac!) AND the good old analog ac Märklin will work.
But using it in an analog dc system, including all scales, will most certainly not function at all.

The board, professionally made.

though parts are reasonably small,
it is still a rather simpel unit for do it yourself.
In the GCA-kits these resistors are all 125 mW small metal film types.

The hardware

gca94-en.txt · Last modified: 2023/01/21 16:15 by phg