Table of Contents
GCA174 DCC/Motorola decoder for GCA145
Direct decoder for Motorola or DCC
This board is based on the design of digital-bahn.de.
The firmware , copyright of Digital-Bahn.de, is available at http://www.digital-bahn.de/bau_led/led_schalten.htm#download
This board is only attachable to J5 of GCA145/MGV145.
It features the 7 outputs, needed to select position 1..48 on GC145/MGV145.
Also an isolated feed-back is provided.
Feed-back is free to be used with systems like S88.
The on-board opto-couplers isolate the didital rail signals and feed-back from the board.
Feed-back is very nice inside Rocrail environment, because it can signal Rocrail to start a train AFTER the selected postion has been reached.
The prototype
 | The board with opto-couplers ready to be connected to GC145 |
Hardware files of protoype
The final board design
| board in production, coming in short term |
Hardware files for final GCA174 design
Address selection
Basicly, the firmware from Digital-bahn.de comes with adress 1..7.
By pressing the button, the decoder is in learning mode, showing D1 to flash.
All you have to do now, is sending the first address from your central unit.
After that, just pwer off GCA145 and power on again.
The addresses of the next ports will be automaticly set in following sequence
One other option is to download hex_minipu from this page: http://www.digital-bahn.de/bau_pic/hexmanipu.htm#download .
It will give you the option to directly change adresses and store them, before programming the chip.
Feed-back
GCA174 has a feed-back signal, to inform Rocrail that turntable is ready to move trains on/off.
This feed-back signal is electrical (galvanic)isolated from the GCA174.
By connecting J2 pt 1(-) and 2(+) to any device like S88 units or derivates,
Rocrail will receive this port condition.
Settings in Rocrail , see Position sensor
Led signals
GCA174 is priovided with 6 yellow leds for indication of decoded turntable position.
The red led(D7) shows the write signal ( in Rocrail, look for 'new Position Flag' ), to inform GCA145 to start responding on the given position.
Connections of GCA174
Extra modification on GCA145(MGV145)
GCA174 needs 5 Volt which is by default not available from J5 on GCA145.
Therefore, this diode 1N4003 (or equivalent) should be mounted under J5 as this picture shows.
NOTE: The latest green pcb has this diode(D10) on board, so no further attention needed.
