RTB_D20

My Homebrew D20 decoder is a double sided mobile decoder with NEM-651 connector. The decoder is designed to integrate into the RTB digital control infrastructure.

See also

• RTB_D12 - custom (Fleischmann V100)
• RTB_D13 - custom (Minitrix coach)
• RTB_D15 - custom (Minitrix V160)
• RTB_D16 - NEM651
• RTB_D21 - Next18
• RTB_D22 - Plux16
• RTB_D23 - NEM652

User Guides

• User Guide - DE
• User Guide - EN

The decoder has the following features,

• NEM-651 connector
• DCC
  • DCC-A automatic logon
  • DCC-R protocol extension
  • Service Mode Programming
• Railcom
  • Channel 1/2
  • POM, xPOM
  • DYN: Speed, QoS, Track-voltage, Motor-current, AUX-current, Temp, Distance travelled
• Double sided
• Dimension: 14 x 8 mm
• 7-20V track voltage
• heartbeat LED
• adjustable max motor current (default 300mA)
• adjustable max AUX current (default 500mA)
• over temp protection
• Function output: LF/LR (dimmable, 1.4kHz) open drain
• Function output: AUX1/AUX2 (dimmable, 1.4kHz) open drain and logic level (3.3V)
• Function output: AUX3/AUX4 logic level (3.3V)
• optional external buffer capacitor (max. 1500uF)
• <10mA idle power consumption
• Firmware update over main tracks via DCC-R protocol

Hardware

The current PCB layout uses SMD footprints with 0.5mm pitch, 0402 and 0201 parts. Reflow soldering is mandatory.

PCB

• 6-layer PCB, FR4, 14 x 8 x 0.8mm (double sided)
• CPU: AVR64DD28
• Motor bridge: DRV8231
• Connector: NEM-651

Kicad

Schematic | Layout | Gerber

Dependency

:yellow_circle: Requires my Kicad project library RTB_SamacSys in the same directory tree.

Firmware

Filename structure: { pcb }{ code }{ version }.hex

Example: D20F0001.hex

	Description
pcb	Name of matching hardware (D20)
code	Type of code contained (R=rom, B=bootloader, F=flash, U=bld update, P=UPDI factory code)
version	Release version (####)

Firmware files

UPDI

The fuse settings as well as the P-code (D20Pxxxx.hex) has to be installed by using UPDI.
Connecting the decoder via its track pins to a 5V(DC) power supply will boot its CPU. This way, its easy to program the fuses and flash.

<img src=supplemental/images/D20_updi.jpg width=800>

Details

Fuse Setting	P-code Install
<img src=supplemental/images/D20_updi_fuses.jpg width=500>	<img src=supplemental/images/D20_updi_memory.jpg width=500>

Images

top	bottom

YouTube

Some YouTubes to see the D20 decoder in action.

This project is intended for hobby use only and is distributed in accordance with the Apache License 2.0 agreement.