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GCA-Pi05 G-Loco Controller


The RocNetNode supports Mobile commands for controlling the GCA-Pi05.
The GCA-Pi05 is designed for gauge G locomotives with enough room to hold a RasPi/Pi05 sandwich.
The Raspberry Pi communicates by WiFi.
Startup of Rasberry Pi is not like a normal DCC locdecoder, it takes approx 8-10 seconds.
Therefore, also a small 6 Volt Accubattery should be mounted inside the loc.
The power supply will also take care for charging the battery and switch it off if for a longer period no power is available from the track.


  • RFID reader for reporting scanned tags between the tracks; Sensor by ID.
  • 4A Motor PWM output: GPIO 22 and 7-8 for direction.
  • 2 Smoke generator channels: 7-8.
  • 6 light PWM channels direction dependent: 9-14.
  • 6 Servo channels: 1-6.
  • 2 general channels: 15-16.
  • Sounds from SD-Card.
  • Hall sensor for controlling the drive wheel speed.

Loco address

Motor setup

The motor PWM frequency is about 100Hz.
The maximal duty cycle can be set as percentage in the steps field; 100% is maximal.
Acceleration can be set in the mass field: 1=10ms, 10=100ms, …
The number of internal speed steps is fixed at 100 and is spread over the maximal duty cycle set in the steps field; For max. duty cycle of 50% the number of decoder steps must be set to 50.

Sensor setup

The reported RFID must mach with a Sensor-ID in Rocrail.
This sensor should have its address set to zero.
The ID must be set in this notation: RFID Notation
The Rocrail traces can be used to copy this ID or the Sensor Monitor.


The RasPi needs a good WiFi USB-Stick to get a stable connection.
In the test environment an EdiMax EW-7711UAn is used. (€10)
The EdiMax Nano can not be used.



For this example a USA Trains EMD GP7 has been used.

  • Max. 65 MPH (104 KM/H)
  • Drive wheel diameter is 28mm; One rotation is 88mm.

RPM Control


In the gear-wheel 3 magnets of 6mm ø3mm must be mounted like this:

Hall Sensor

The Hall sensor can be tie-wrapped on a small piece of PCB which fits beside the gear-wheel in the gear-box of one truck.
After the sensor have been bent in the optimal position it can be fixated with some hot glue.
The Hall sensor will generate three times a pulse for every wheel rotation.

rpm-hall-position1.jpg rpm-hall-position2.jpg
Position for the PCB board. Mounted PCB.
another way to mount the hallsensor
on the other side of the housing

DC Voltage Hall Freq. Rotations Scale speed
2V 3Hz 1 10 kmh
6V 10Hz 3.33 35 kmh
12V 22Hz 7.33 67 kmh
18V 33Hz 10 100 kmh

RFID Reader

The RFID reader can be mounted in the Cylinders (19). Or alternatively in the tank. (20)

rfid-reader-position-1.jpg rfid-reader-position-2.jpg

The ID-12LA in combination with glass responders is fast enough for this gauge.

Motor distortion

The motors usually are spreading a lot of distortion, which is suppressed mostly on the controller board or decoder.
But the rather long lines to the motor still spread a lot of this distortion,
and in that way making a good functioning of the RFID sensor rather impossible.
One good solution is using VDR resistor (plain 30V type) , mounted directly on the motor connections.
This actually cured my RFID problem.
Picture below shows one of the VDRs mounted.


gca-pi05-en.txt · Last modified: 2019/04/18 14:26 by rjversluis