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GCA104 separation switch for 2 booster or booster / transformer


By Peter Giling


There are still many rail hobbyists, who like to use a standard transformer for old analoque trains in combination with digital equipment.

Many of them probably might have experienced that connecting together (by accident of course!) booster and 'old' transformer, will result in a defective digital central.

To avoid this problem , Maerklin used to supply a ' wippe' which makes the central slider turn over from one connected rail to another.

This item is no longer available from this train supplier.

But that was only for the three rail drivers.

For two rail drivers, the problem is more serious, because all wheels of the entire train will shortly connect the two systems together for shorter or longer time.

Taking these problems in consideration, I would suggest to forget the 'old' way of running trains. With the now available good and affordable decoders it is a better solution to change to digital all the way.

But persisting in this ananlogue driving, here is a solution, more complicated than the ' wippe', but nevertheless very useful for the same task.

The unit is made with a PIC12F675 processor. The program for it is written in PicSimulatorIDE (

How does it work?

GCA104 works in both directions. Download the schematics. The connection diagram is included.

The brown wire (or black DCC) is connected straight to rails.

The red wires from both boosters or booster/ trafo should be connected to appropriate terminals.(e.g. Booster 1 and booster 2)

There are three sections with a current detector e.g. section A, C, and E.

Section B and D are just separation sections to avoid short circuit under all circumstances.

Two directions are possible:

1) From section A to E:

When entering in Section A, section B,C and D will switch to Booster 1.

Entering Section C wil cause switching section B,C and D to booster 2.

When train follows into section E, nothing will change anymore.

2) From section E to A:

When entering section E, section B,C and D will switch to booster 2.

Entering section C, will cause switching section B,C and D to booster 1.

When train follows into section A nothing further will happen.

Important notes

*) All sections must be driven over in one direction, so never change direction inside these 5 sections!

*) Any booster system like Digitrax system , with no common brown ac wire, cannot be used. (Also not with the Maerklin ' wippe').

For 3 rail system :

*) All sections need to be longer then the longest slider. But when any of the following waggons is also using a slider for illumination or anything else, each section needs to be longer that the maximum distance between those sliders.

This of course considering that the change of connection from on booster/trafo to the other is done in the mid-rail.

For 2 rail system :

Each section needs to be longer than the longest train.

The ready made unit

The Pc-board info

Bill of materials

Item Quantity Reference Part
1 3 R1,R2,R3 33E
2 3 R4,R5,R6 10K
3 2 R7,R8 330E
4 1 C1 ELCO 100 uF 25V rad
5 1 C2 ELCO 10 uF 25V rad
6 1 C3 100 nF
7 2 Led1,Led2 LED 3 mm
8 1 D1 DIODE 1N4148
9 4 GR1,GR2,GR3,GR4 B80C1500
10 1 U1 PIC12F675 with 8-pin socket
11 1 U2 K847P with 16-pin socket
12 1 VR1 7805
13 1 J1 SCREW-07
15 4 F1 FUSE MFR 0,3A
16 3 F2,F3,F4 Fuse MFR 0,9 A

The schematics and how to connect it

The firmware

mgv104-en.txt · Last modified: 2018/11/12 08:56 (external edit)