A simple Arduino model train control (DCC) system acts as a command station to control DCC decoders.
This project adapted Michael Blank's program code for signal generation. The original program supports one decoder only. This program supports up to 9 decoders and provides a command controls interface on the serial port. Because of that, you don't need extra hardware components such as a keypad or potentiometer to control trains. The only thing needed is the serial monitor on your computer. This also makes it easy for you to develop a human interface system to work with this program.
The program generates two opposite DCC signals. When one signal goes HIGH, the other goes LOW, and vice versa. That means you can connect them to an H-bridge circuit to boost the signal to power the track and locomotives.
The program uses the hardware timer and interrupts to achieve the precise pulse width generations of the DCC signal. The following Arduino boards are supported.
- Arduino UNO (Other boards based on ATmega328p may be supported)
- Timer 2 is used
- Arduino UNO WiFi Rev.2 and Arduino Nano Every (Other boards based on ATmega4809 may be supported)
- TCB0 is used
You must use an H-bridge circuit or a motor driver module to deliver the amount of current used by locomotives and their motors. Do not connect any Arduino pins to the track or locomotives directly. Also, you must use an external power source instead of the USB 5v to power the H-bridge/motor driver. The nominal voltages limit for N and HO scales are 12v and 15v respectively according to the NMRA standard (S-9.1).
Pin 11 and 12 provide a pair of opposite DCC signals. Connect them to the two direction pins of the H-bridge. If you use a motor driver with only one direction pin, use either Pin 11 or 12. Connect the two output pins of the H-bridge/motor driver to the track.
The Enable signal at Pin 10 will go HIGH when the program start generating DCC signals. Connect this pin to the enable or PWM pin of the motor driver. This pin is important if your motor driver only uses one pin for direction control. Arduino takes around 0.5s to boot up. Without DCC signal waveforms during this period, the motor driver may output a static DC voltage to the track. This short time is long enough to trigger some DCC decoders to operate in DC mode, leading the motor to spin at full speed unexpectedly. This pin ensures the motor driver turns on only when the program is ready.
Add the following codes to setup(). Connect the channel A output to the track.
pinMode(3, OUTPUT);
digitalWrite(3, HIGH); // sets PWM (EN1 of L298) HIGH
pinMode(9, OUTPUT);
digitalWrite(9, LOW); // disables the brake function of the shield
- Download and unzip the project.
- Open the folder "Arduino-DCC-Station" with Arduino IDE.
- Upload the sketch to your Arduino board.
- Connect the Arduino to the H-bridge circuit and the track.
- Open Serial Monitor and send control messages (see below) to control your locos.
The program reads control messages from the default serial port and generates corresponding DCC signals. The states of locomotives, including the direction, speed step and function ON/OFFs of F0-F20 (F0 refers to headlight), are stored in the SRAM so the system will output DCC packets to the rails continuously without having the need of resending control messages.
Each message is enclosed by "<>" and has the following format:
Type (1 byte), Address (1 byte), Payload
<SADVVV>
This type of message controls the direction and speed step of a locomotive. The payload consists of 1 byte of direction D [0 (backward),1 (forward)], followed by 3 bytes of 128 speed step VVV [000-127].
Sets the speed of address 3 decoder to forward direction and speed step 5.
<S31005>
- Type: S
- Address (A): 3
- Payload
- Direction (D): 1
- Speed Step (VVV): 005
<FAUUE>
The payload consists of 2 bytes of function index F0-F20 UU [00-20], followed by 1 byte of on/off E [1,0].
- F0 is the function control of the headlight.
Turns ON the F2 of address 3 decoder.
<F3021>
- Type: F
- Address (A): 3
- Payload
- Function (UU): 02
- ON/OFF (E): 1
<E>
Stop all locomotives. This message will instruct all digital decoders shall stop delivering energy to the motor.
<R>
Resume normal operation. Locomotives will remain stationary unless a new speed step is set.
<W>
Reset the Arduino in software. After reset, the station sends out reset packets to locos until a valid control command message is received.
When the Arduino startup, the program will send out reset packets continuously until a valid control command message is received from the serial port. This ensures all locos in the track stop running after the Arduino reset.
Some control packets are sent repeatedly as per the requirement of NMRA standard (S-9.2) and to keep the consistency of the controller and locos’ behaviours. The NMRA standard only mentioned packets should be repeated as frequently as possible but did not define how a particular packet should be repeated. This program has the following approach.
The program consists of two packet pools, which can be considered as output buffers. The priority pool, implemented as a queue (FIFO), stores packets to be sent first. The repetitive pool, implemented as a circulated array, stores packets that need repetition of output. Each slot in the repetitive pool is dedicated to a specific type of packet of a loco address. Six types of packets are needed for one loco. Hence, each loco occupies six slots in the repetitive pool. Packets stay there, and one is replaced by a new one when the associated state of the loco changes.
| Type of Packet | Function |
|---|---|
| Advanced Operations Instruction | 128 Speed Step Control |
| Function Group One Instruction | FL and F1-F4 Function Control |
| Function Group Two Instruction (F5-F8) | F5-F8 Function Control |
| Function Group Two Instruction (F9-F12) | F9-F12 Function Control |
| Feature Expansion Instruction (F13-F20) | F13-F20 Function Control |
| Feature Expansion Instruction (F21-F28) | F21-F28 Function Control |
When a control message comes, two identical packets of the corresponding command are pushed to the priority pool and one is written to the specific slot in the repetitive pool. The second packet to the priority pool compensates the first in case the first is lost during transmission. When a packet is available in the priority pool, the DCC signal generator will fetch the packet from there for the next output. This ensures that locos can act instantly to the control message. Once a packet is fetched from the priority pool, it is erased.
When the priority pool is empty, the generator fetches a packet from the respective pool in turn. Since packets in the repetitive pool stay there during the system lifetime, the system can continuously output meaningful packets even when no control message comes and keep locos' behaviours consistent with the controller.
You should take your own risk to use anything in this project. The author of the project is not responsible for any damage, hurt, or other kinds of accident caused by the use of the program code and the suggested electronic components.