README.md
rp2040-decoder-e24

DIY DCC decoder for model railroad locomotives in an E24 form factor suitable for N scale/gauge locomotives

Features


4x MOSFET-switched functions
5x GPIO pins (3.3V input/output)
Up to 0.75A motor current
E24 form factor (19.5mm x 8.5mm)
i2s audio output chip (software support forthcoming)
12V nominal rail voltage (16V max)


USB Programmer/E24 Tester Features


USB-C port and SWD header for programming/debugging
Built-in front/rear "lamp" LEDs for decoder testing
Breakout header for most E24 pins, including speaker, motor, and 9 functions
Rail contact pads on underside of board allow for testing the decoder as a stationary dummy-loco as well as CV programming on N-gauge track


E24 Receiver Breakout Board Pinout




  
E24 Pin
  
Function
  
GPIO Pin




  
1
  
Speaker+
  
USB D+


  
2
  
Speaker-
  
USB D-


  
3
  
GND
  
GND


  
4-5
  
Motor-
  
N/A


  
6-7
  
Motor+
  
N/A


  
8
  
Cap+
  
Not connected


  
9
  
Lamp Front
  
GPIO26 (MOSFET)


  
10
  
Lamp Rear
  
GPIO27 (MOSFET)


  
11
  
AUX1
  
GPIO24 (MOSFET)


  
12
  
AUX2
  
GPIO25 (MOSFET)


  
13
  
AUX8
  
Not connected


  
14
  
AUX7
  
Not connected


  
15
  
AUX6
  
Not connected


  
16
  
AUX5
  
Not connected


  
17
  
U+
  
DC Rail Voltage


  
18
  
Vcc
  
3.3V


  
19
  
AUX10
  
GPIO0


  
20
  
AUX4
  
GPIO4


  
21
  
AUX3
  
GPIO3


  
22
  
GND
  
GND


  
23
  
AUX11
  
GPIO1, SWD


  
24
  
AUX12
  
GPIO2, SWCLK


  
N/A
  
Back EMF A
  
GPIO29


  
N/A
  
Back EMF B
  
GPIO28


  
N/A
  
Rail signal decoder
  
GPIO21


  
N/A
  
Status LED
  
GPIO12


  
N/A
  
i2s LRCLK
  
GPIO5


  
N/A
  
i2s BCLK
  
GPIO6


  
N/A
  
i2s DIN
  
GPIO7


  
N/A
  
Enable external keepalive capacitor
  
GPIO16




Images

RP2040 Decoder E24




RP2040 Decoder USB Programmer




E24 Receiver/Wire Breakout




Based on the rp2040-decoder project by gab-k: <![CDATA[]]>https://github.com/gab-k/RP2040-Decoder<![CDATA[]]>

Reference:


RCD-124 (German): <![CDATA[]]>https://normen.railcommunity.de/RCD-124.pdf<![CDATA[]]>
<![CDATA[]]>https://dccwiki.com/Locomotive_Interface/E24<![CDATA[]]>


View this project on CADLAB.io.