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GCA125 Interface for motordriven turnouts


By Peter Giling

Features and facts

8 individual inputs, commanding 8 individual outputs

600 mA max load per output.

Max 42 Volt per output.

8 individual inputs.

Time selection for output duration.

Outputs are activated one by one for power reduction.

The prototype



Controlling a LGB 1201, Kato or Fulgurex turnout-drive, in fact also some type of Hoffmann turnout motors, only have one coil or motor, that needs to be controlled by polarity.
Even the Bohler WA2 is very nicely useable with this interface.
The normal driver like GCA77 is not suitable for that.
The complexity of this unit is slightly higher.
In the GCA units, it is standard, to separate the power, needed to activate the coils and the LocoNet system by means of optocouplers.
This unit is able to control 8 turnouts, and need 8 inputs from the GCA50.
So 2 units, capable of a total of 16 turnouts, are commanded by 1 GCA50.
It is also possible to use a switch for direct activation without GCA50.
You will need a 5-12Vdc to activate the opto-couplers.
The software in the PIC16F62x is made in such a way that the processor provides a correct timing for the coil, and switch it off after the chosen time.
This will take care that the turnout coil will not be overheated by too long powering.
The time selection is done with the Dipswitch.
The processor in the circuit needs 8 inputs and 16 outputs, and 3 extra for dip-switch reading.
The smaller PIC processors have only maximum 16 I/O.
Therefore I used I2C expanders , making a small processor suitable.\\

The hardware files

The schematics
The pcb Layout
N.B. Self made pc-boards are not supported!

Cable to MGV50 / CAN-GC2


Time delay settings

SW1 is used to set the delay time after which the output will be swotched off.

Delay table
Delay in Sec SW1 1 SW 2 SW 3
0.1 Off Off Off
0.2 Off Off On
0.4 Off On Off
0.8 Off On On
1.6 On Off Off
3.2 On Off On
6.4 On On Off
12.8 On On On


Inputs, if activated, should remain activated, to keep motor/coil in the chosen position.

GCA50 should be programmed as switch, with C2 NOT checked.

Checking C2 will inverse action.

Bill of materials

Qty Reference Description
8 R1..8 1 kOhm
2 R9,10 3.3 kOhm
3 R11…13 10 kOhm
1 RP1 8x 10 kOhm SIL-9
1 C1 1000 uF 35V radial
1 C2 10 uF 35V radial
3 C3..5 capacitor 100 nF
1 VR1 Power IC 7805 (TO-220)
1 U1 Processor PIC16F627 or equiv.
1 socket 18Pins for U1
2 U2,U3 PCF8574
4 U4..7 L293D (DIL-16)
2 U8,9 LTV847 or equiv.
8 Socket Dil16
1 GR1 Bridge B80C1500 round
1 F1 PFRA110 mulitfuse 1.1A
4 J1 AKL012-04
1 J2 AKL012-02
1 SW1 dip-switch 3
gca125-proto-en.txt · Last modified: 2018/11/12 08:56 by