Trailer Decoder
The Trailer Decoder
General
Why was a special trailer decoder developed?
Previously, a large number of wires were required to power the lighting on a trailer.
- With light vehicles, the trailer hangs rigidly on the cables and does not steer.
- Trailers with many cables are difficult to connect and disconnect.
- With semi-trailers, it is not easy to route the many wires through the kingpin.
This decoder is not only suitable for vehicles with trailers. This also allows the number of outputs to be increased to connect more lights.
The trailer decoder essentially consists of the familiar decoder hardware, but with special software.
The trailer's turn signals, etc., are switched on or off synchronously with the towing vehicle.
The lights will only light up when the towing vehicle sends a signal.
When switched on, the trailer decoder does not display the turn signals or brake lights like a towing vehicle.
What is transmitted
| DC05-..A | Tail light | Brake light | Left turn signal | Right turn signal | Distance |
| Blue light | Front flasher | Light 1 | Light 2 | Light 3/4 | |
| DC07-..A | Taillight | Brakelight | Left turn signal | Right turn signal | Distance |
| Blue light | Front flasher | Light 1 | Light 2 | Light 3 | Light 4 |
Distance control with a trailer:
The rear infrared LEDs connected to the trailer decoder only send the distance signal.
No feedback signal can be transmitted for the XT module!
The distance signal can be DC05-A or DC05-S-A cannot be switched off.
With the DC07 trailer decoder from 2019, the distance signal can be switched off.
Battery charge level:
If the trailer has its own battery, it can also be monitored with the decoder.
Light sensor:
If the towing vehicle has a light sensor, the trailer does not require an additional light sensor.
The trailer's lighting is switched on or off synchronously in this case.
Connection to towing vehicle to trailer
Only 2 cables are required if the trailer has its own battery.
3 cables are required if the trailer is powered by the towing vehicle.
Wireless trailer
For an extension to the wireless trailer, see Wireless trailer
Options and connection
see Trailer Decoder Connection
Decoder Settings
Set the CV20 in the train decoder to a value of 4.
Set the CV21 in both decoders: Value 0, 4, or 24. Default as of July 2019: Value: 4
Otherwise, the lights on the trailer may flash randomly or nothing will happen at all.
How to set the trailer decoder:
- Use the CV Programmer on the update socket.
- Connect the IR receiver connection of the trailer to the connection of the towing vehicle IR receiver (not the IR LED). The trailer will then respond to the IR signals like the towing vehicle. If you first change the decoder address in the towing vehicle, e.g., CV1=5, you can then connect the trailer and continue to change settings via address 1 without changing the towing vehicle settings.
- Connect the DC07-A with a 470 kOhm resistor to the IR receiver and the negative terminal to the digital connection of a DCC system.
- Trailer decoders with built-in IR receivers DC07-SI-A (=DC05-SI-A), DC07-I-A (=DC05-I-A) can be adjusted directly with the digital control center, provided an IR transmitter is connected to it (e.g., an IR emitter or Progset).
A phototransistor is connected to the phototransistor input, just like on the towing vehicle.
DC07 trailer decoder from June 2025
Adjustment via CV120 and CV121 with the CV programmer from 580_V7_40.
The further development is the DC07 trailer decoder.
DC07A, DC07SA, DC07IA, DC7SIA are compatible with the DC05xxx.
but have additional functions.
- Disabling the rear distance control with a light function. CV120
0 = No function 4 = Light 2 turns off the rear IR LED 8 = Light 3 turns off the rear IR LED 16 = Light 4 turns off the rear IR LED 32 = Blue light turns off the rear IR LED 64 = Front flasher turns off the rear IR LED
- Use of the transistor to switch 500mA, e.g., displays or sound modules CV121
0 = No function 4 = Light 2 turns on the transistor 8 = Light 3 turns on the transistor 16 = Light 4 turns on the transistor 32 = Blue light turns on the transistor 64 = Front flasher turns on the transistor
- With CV21=0, the trailer can also be tested without a towing vehicle (CV programmer V7 or higher required!)
On Update of DC05...A is possible through the DC-Car-Service.
Wireless_Trailer
The SerOut signal can be sent to an IR-LED.
With a phototransistor and an amplifier, the signal can be routed to the trailer decoder SerIN.
The DC07-SA is ideal for this purpose.
The electrical parts, including a battery, switch, charging socket, and reed switch, are offered in a set.
Instructions: Wireless_Trailer
Note
No motor can be operated on the trailer decoder, even if the transistor is present for production reasons!
Special cases with DC05...A
With a small modification, the motor connection
can be used as a powerful Light 2 output.
Procedure: Disconnect the circuit at the red dot and
wire a blue bridge to the Light 2 control.
This allows components up to 500 mA to be connected.
For the transistor to switch negative when activated,
CV69 must be set to 1.
The previous Light 2 output now works in reverse.
Since the IR LED cannot be switched off on the DC05...A, a trick must be used.
The positive pole of the IR LED is connected to sound.
The negative pole, as before, to the IR LED.
Now you can switch off the rear LED with the front flasher or sound.
Battery test as a warning:
Since trailers with their own batteries must also be turned off, the battery test should be used.
The hazard warning lights will turn on when the voltage falls below the set value.
