README.md
rp24-dcc-decoder

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




Features


8x MOSFET-switched functions
5x GPIO pins (3.3V input/output)
Up to 0.75A motor current
E24 form factor (approx 20mm x 9mm)
i2s audio speaker output
12V nominal rail voltage (16V max)


USB Programmer/E24 Tester


- USB-C port for easy programming and loading sound files
- Onboard LEDs for all aux outputs for simple decoder testing
- Breakout header for most E24 pins, including speaker, motor, rectified rail power, Vcc, plus all five E24 GPIO pins (Aux 3, 4, 10, 11, 12)
- Programming track input header allows for stationary decoder testing and CV programming

RP24 Decoder 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+
  
GPIO20


  
9
  
Lamp Front
  
GPIO6 (MOSFET)


  
10
  
Lamp Rear
  
GPIO7 (MOSFET)


  
11
  
AUX1
  
GPIO8 (MOSFET)


  
12
  
AUX2
  
GPIO5 (MOSFET)


  
13
  
AUX8
  
GPIO4 (MOSFET)


  
14
  
AUX7
  
GPIO3 (MOSFET)


  
15
  
AUX6
  
GPIO9 (MOSFET)


  
16
  
AUX5
  
GPIO2 (MOSFET)


  
17
  
U+
  
DC Rail Voltage


  
18
  
Vcc
  
3.3V


  
19
  
AUX10
  
GPIO10


  
20
  
AUX4
  
GPIO13


  
21
  
AUX3
  
GPIO14


  
22
  
GND
  
GND


  
23
  
AUX11
  
GPIO0


  
24
  
AUX12
  
GPIO1


  
N/A
  
Motor Driver A
  
GPIO25


  
N/A
  
Motor Driver B
  
GPIO26


  
N/A
  
Back EMF A
  
GPIO28


  
N/A
  
Back EMF B
  
GPIO29


  
N/A
  
ADC Reference (ADC pin connected to GND)
  
GPIO27


  
N/A
  
DCC signal TTL
  
GPIO21


  
N/A
  
RailCom Out
  
GPIO11


  
N/A
  
Status LED
  
GPIO19


  
N/A
  
i2s DIN
  
GPIO22


  
N/A
  
i2s BCLK
  
GPIO23


  
N/A
  
i2s LRCLK
  
GPIO24


  
N/A
  
Charge external keepalive capacitor (PWM at very low duty cycle only)
  
GPIO20




E24 Receiver/Wire Breakout Board




Receiver Board Solder Pads




  
E24 Pin
  
Function
  
Label




  
1
  
Speaker+
  
SPK


  
2
  
Speaker-
  
SPK


  
3
  
GND
  
G


  
4-5
  
Motor-
  
- MOTOR +


  
6-7
  
Motor+
  
- MOTOR +


  
8
  
External Capacitor+
  
C


  
9
  
Lamp Front
  
F LAMP R


  
10
  
Lamp Rear
  
F LAMP R


  
11
  
AUX1
  
1


  
12
  
AUX2
  
2


  
17
  
DC Rail Voltage
  
RV


  
18
  
Microcontroller Voltage Output
  
Vcc


  
19
  
AUX10
  
10


  
20
  
AUX4
  
4


  
21
  
AUX3
  
3


  
22
  
GND
  
G


  
23
  
AUX11
  
11


  
24
  
AUX12
  
12




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

Reference:

E24


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


RailCom


<![CDATA[]]>NMRA S-9.3.2, Section 2<![CDATA[]]>
Example RailCom transmitter circuit: <![CDATA[]]>CircuitJS<![CDATA[]]>


View this project on CADLAB.io.