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GCA125 Interface for turtoise type turnout drives


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.


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.
For GCA drive-units it is standard, to have an isolation between power for the coils or motors and the LocoNet system by means of optocouplers.
That is also done on this board.
The processor runs on 5V from GCA50 / CAN-GC2 or GCA_PI02, and the processor drives two optocouplers to send I2C commands to expanders.
This unit is able to control 8 turnouts, and need 8 inputs from the GCA50 / CAN-GC2 / GCA_PI02.
It is also possible to use a switch for direct activation without GCA50 / CAN-GC2 / GCA_PI02.
You will need a 5 Vdc to activate the processor.
One other option is to use GCA174 DCC or Motorola function decoder, to drive directly from the central unit.
The software in the PIC16F628 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 or motor will not be overheated by too long powering.
The time selection is done with the Dipswitch, and counts for all outputs.
The processor in the circuit needs 11 inputs and 18 outputs, and 3 extra for dip-switch reading.
Instead of these 29 I/O ports, smaller PIC processors have only maximum 16 I/O.
Therefore I used I2C expanders, adding 16 extra outputs and making a small processor suitable.\\

Old version

The hardware files

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

Cable to GCA50 / CAN-GC2 / GCA_PI02


Time delay settings

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

Delay table
Motor activation
in Sec
SW1.1 SW1.2 SW1.3
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/CAN-GC2/GCA_PI02 ports should be programmed as switch, with C2 NOT checked.

Checking C2 will inverse action.

mgv125-en.txt · Last modified: 2018/11/12 08:56 by