Small project for a 'Shuttle Yard' control using a linear actuator with a stepper motor driver using an Raspberry Pi Pico W.
Supports WiFi providing a Telnet commandline interface, a web interface and REST web api setup for testing the application.
License: MIT
The stepper motor is a typical NEMA 23 motor with the following characteristics:
Step Angle: 1.8° (200 steps per revolution)
Max. PRM: 600
Phases: 2
Rotor Inertia: 280 g/cm²
Mass: 0.72 kg
Rated Voltage: 3 V - 36 V
Rated Current: 2.8 A
Holding Torque: 1.26 Nm
Detent Torque: 45 mNmWith higher frequency the usable torque is decreased considerably.
The stepper motor driver used is a DM542T and allows microstepping up to 128. The DM542T (V4.0) is designed to operate within 18 - 50VDC voltage input. The minimum pulse width is 2.5 μs.
The DM542T(V4.0) has one 8-bit DIP switch and one 1-bit selector. The first 8-bit is used to configure settings of micro step resolution, output current, motor standstill current, pulse type and smoothing time as shown below.
| SW1 | SW2 | SW3 | SW4 | SW5 | SW6 | SW7 | SW8 |
Output Current Idle Microstep
Current
Microstep resolution is set by SW5, 6, 7, 8 of the DIP switches as shown in the following table.
| Microsteps | Steps/rev. | SW5 | SW6 | SW7 | SW8 |
|---|---|---|---|---|---|
| 1 | 200 | ON | ON | ON | ON |
| 2 | 400 | OFF | ON | ON | ON |
| 4 | 800 | ON | OFF | ON | ON |
| 8 | 1600 | OFF | OFF | ON | ON |
| 16 | 3200 | ON | ON | OFF | ON |
| 32 | 6400 | OFF | ON | OFF | ON |
| 64 | 12800 | ON | OFF | OFF | ON |
| 128 | 25600 | OFF | OFF | OFF | ON |
| 5 | 1000 | ON | ON | ON | OFF |
| 10 | 2000 | OFF | ON | ON | OFF |
| 20 | 4000 | ON | OFF | ON | OFF |
| 25 | 5000 | OFF | OFF | ON | OFF |
| 40 | 8000 | ON | ON | OFF | OFF |
| 50 | 10000 | OFF | ON | OFF | OFF |
| 100 | 20000 | ON | OFF | OFF | OFF |
| 125 | 25000 | OFF | OFF | OFF | OFF |
The first three bits (SW1, 2, 3) of the DIP switch are used to set the dynamic current.
| Peak Current | RMS Current | SW1 | SW2 | SW3 |
|---|---|---|---|---|
| 1.00A | 0.71A | ON | ON | ON |
| 1.46A | 1.04A | OFF | ON | ON |
| 1.91A | 1.36A | ON | OFF | ON |
| 2.37A | 1.69A | OFF | OFF | ON |
| 2.84A | 2.03A | ON | ON | OFF |
| 3.31A | 2.36A | OFF | ON | OFF |
| 3.76A | 2.69A | ON | OFF | OFF |
| 4.50A | 3.20A | OFF | OFF | OFF |
- Step & direction (PUL/DIR) control
- Input voltage 20-50VDC (recommended 24-48VDC)
- 200 KHz max pulse input frequency
- 16 microstep resolutions of 200-25,600 via DIP switches
- 8 output current settings of 1.0-4.5A via DIP Switches
- Idle current reduction to 50% or 90% selection via SW4
- Auto-tuning to match wide-range NEMA 11, 17, 23 and 24 stepper motors
- Anti-Resonance for optimal torque, extra smooth motion, low motor heating and noise
- Soft-start with no “jump” when powered on
- Optically isolated inputs with 5V or 24V
- Fault output
- Over-voltage and over-current protections
| Input | Current 0~5.0A |
| Output | Current 0.5-4.0A |
| Power (MAX) | 160W |
| Micro Step | 1, 2/A, 2/B, 4, 8, 16, 32 |
| Temperature | -10~45 °C |
| Humidity | No Condensation |
| Weight | 0.2 kg |
| Dimension | 965633 mm |
Signal Input
PUL+ Pulse +
PUL- Pulse -
DIR+ Direction +
DIR- Direction -
EN+ Off-line Control Enable +
EN- Off-line Control Enable - Signal Output
ALM+ Fault output +
ALM- Fault output -Motor Machine Winding
A+ Stepper motor A+
A- Stepper motor A-
B+ Stepper motor B+
B- Stepper motor B-Power Supply
VCC VCC (DC9-42V)
GND GNDWhen over voltage or over current protection happens, DM542T(V4.0) red status LED light will blink and the impedance state between ALM+ and ALM- will change (from low to high or high to low depending on configuration) Note that the ENA input pin of the DM542T is inverted (enabled = LOW) and is optional (connect the ENA input pin to ground).
The Raspberry Pi Pico W is a microcontroller board based on the Raspberry Pi RP2040 microcontroller chip and has been designed to be a low cost yet flexible development platform for RP2040, with a 2.4GHz wireless interface and the following key features:
- RP2040 microcontroller with 2MB of flash memory
- On-board single-band 2.4GHz wireless interfaces (802.11n)
- Micro USB B port for power and data (and for reprogramming the flash)
- Exposes 26 multi-function 3.3V general purpose I/O (GPIO)
- 23 GPIO are digital-only, with three also being ADC capable
- Can be surface-mounted as a module
- Dual-core cortex M0+ at up to 133MHz
- On-chip PLL allows variable core frequency
- 264kB multi-bank high performance SRAM
- On-board USB1.1 (device or host)
- 30 multi-function general purpose I/O (four can be used for ADC)
- 12-bit 500ksps analogue to digital converter (ADC)
Since the Raspberry Pi Pico W GPIO support 3.3V and the DM542T stepper motor driver provides 5V inputs, the TXS0108 logic level shifter is used.
- Bi-directional
- Automatic direction control
- 1.2 Mbps (open drain)
- Low voltage 1.4 to 3.6 V
- High voltage 1.65 to 5.5 V
- Dimensions: 15 mm x 13 mm
Arduino is an open-source hardware and software company, project, and user community that designs and manufactures single-board microcontrollers and microcontroller kits for building digital devices.
The microcontrollers can be programmed using the C and C++ programming languages, using a standard API which is also known as the Arduino Programming Language, inspired by the Processing language and used with a modified version of the Processing IDE.
Support of the Raspberry Pi Pico W is available via the Raspberry Pi Pico Arduino core, Arduino-Pico and can be found at Github (https://github.com/earlephilhower/arduino-pico).
Additional libraries are used. They can be found and installed via the Arduino library manager.
- TelnetLib
- WebServer
- LittelFS
- Blinkenlight
- StringSplitter
- ArduinoTrace
The local modules implement the application settings (read from a JSON file), support for blinking leds, system info, wireless connection, and a command interpreter.
- PicoW.h
- Version.h
- GpioPins.h, GpioPins.cpp
- Actuator.h, Actuator.cpp
- Commands.h, Commands.cpp
- ServerInfo.h, ServerInfo.cpp
- AppSettings.h, AppSettings.cpp
- SystemInfo.h, SystemInfo.cpp
- WiFiInfo.h, WiFiInfo.cpp
- Wireless.h, Wireless.cpp
- appsettings.json
The main module gets the settings, connects to an wlan access point, creates the commands, the web server and the telnet server.
- Create (global) instances.
- Create the onboard led instance.
- Create the application settings.
- Create the input and output pins.
- Create the actuator instance.
- Instanciates the web server (on port 80).
- Instanciates the telnet server.
- Create the commands instance.
- Instanciates the global timer.
- Run the setup() function.
- Start the Serial interface (USB).
- Initialize the LittleFS file system.
- Initialize the Settings (appsettings.json).
- Initializes the GPIO outputs and inputs.
- Initialize the actuator instance.
- Connect to a wlan access point.
- If not successful create local AP.
- If local AP cannot be created, stop.
- Get UTC time using NTP.
- Setup the HTTP requests.
- Start the web server.
- Setup the telnet callbacks.
- Start the telnet server.
- Initialize the global timer.
- Enter loop().
- Update Led.
- Update Inputs.
- Update Telnet.
- Update Http Server.
This class maintain lists of available commands. A command is a class holding the name, an optional shortcut, and a command function pointer (callback).
The following command types are supported:
BaseCommand - A command with an optional shortcut and no arguments.
LongCommand - A command with an optional shortcut and a single long argument.
FloatCommand - A command with an optional shortcut and a single float argument.Public Fields:
JsonOutput - Flag indicating JSON output (telnet).
WaitForResponse - Flag indicating that we wait for a (Yes/No) response.Public Methods:
init() - Initializes the command list.
add() - Creates a new command and adds to the command list.
run() - Parses the input line and runs the command.
help() - Gets a printable help string on the available commands.The follwing info classes are implemented
- ServerInfo
- SystemInfo
- WiFiInfo
- GpioPins
The all provide public fields, initialized in the cunstructor, with various information.
All application settings are maintained here. The settings classses provided are all instantiated reading the application settings file 'appsettings.json'.
- Yard Settings
- Actuator Settings
- Stepper Settings
- Server Settings
- Http -Settings
- Telnet Settings
- WiFi Settings
- AP Settings
{
"Yard": {
"Tracks": [
10000,
23200,
36400,
49600,
62800,
76000,
89200,
102400,
115600,
128800
]
},
"Actuator": {
"LedRunning": 3,
"LedInLimit": 4,
"LedAlarmOn": 5,
"SwitchStop": 7,
"SwitchLimit1": 8,
"SwitchLimit2": 9,{
"Yard": {
"Tracks": [
10000,
23200,
36400,
49600,
62800,
76000,
89200,
102400,
115600,
128800
]
},
"Actuator": {
"LedRunning": 3,
"LedInLimit": 4,
"LedAlarmOn": 5,
"SwitchStop": 7,
"SwitchLimit1": 8,
"SwitchLimit2": 9,
"SmallStep": 1.0,
"MinStep": 0.1,
"Retract": 4.0
},
"Stepper": {
"PinPUL": 0,
"PinDIR": 1,
"PinENA": 2,
"PinALM": 6,
"MinSpeed": 800.0,
"MaxSpeed": 4000.0,
"MaxSteps": 3200,
"MicroSteps": 16,
"StepsPerRotation": 200,
"DistancePerRotation": 8.0
},
"Http": {
"Port": 80
},
"Telnet": {
"Port": 23,
"Prompt": ">"
},
"WiFi": {
"DHCP": true,
"SSID": "Home Lan 42",
"Password": "Yellow31Red21Green41",
"Hostname": "YardControl",
"Address": "10.0.1.222",
"Gateway": "10.0.1.254",
"Subnet": "255.255.255.0",
"DNS": "10.0.1.254"
},
"AP": {
"SSID": "YARD_CONTROL",
"Password": "Yellow31",
"Hostname": "YardControl"
}
}The TelnetLib has been updated to support the delete key (sending a 'space' and 'backspace' when receiveing a 'backspace').
A set of commands are available at the telnet prompt. The 'help' command provides a list of all supported commands:
Yard Control:
Allows to control the linear actuator providing a set of commands.
The following commands with no argument are available:
? | help - Shows this help information.
q | quit - Terminates the program.
j | json - Toggle JSON output mode.
v | verbose - Toggle verbose output.
-
s | status - Shows the current state of the motor driver.
p | position - Shows the current position.
+ | plus - Moves a step forward.
- | minus - Moves a step backward.
f | forward - Moves a 0.1 mm distance forward.
b | backward - Moves a 0.1 mm distance backward.
c | calibrate - Run a calibration sequence.
e | enable - Enabling the output (after disable).
d | disable - Stops the motor by disabling the output.
x | stop - Stops the running motor (decelerating).
h | home - Moves to home position (position = 0).
g | gpio - Shows the GPIO input and output pin values.
yard - Show yard track settings.
pico - Show Pico W pin layout.
wifi - Shows the WiFi information.
server - Shows the server information.
system - Shows the system information.
stepper - Shows the stepper settings.
actuator - Shows the actuator settings.
settings - Shows all settings information.
appsettings - Shows the appsettings file.
reboot - Reboots the RP2040.
reset - Resets the current position to zero.
save - Saves the updated application settings.
load - (Re)loads the application settings.
smallstep - Gets the small move distance (mm).
minstep - Gets the min move distance (mm).
retract - Gets the retract distance (mm).
rpm - Gets the speed RPM.
speed - Gets the speed (steps per second).
minspeed - Gets the minimum speed (steps per second).
maxspeed - Gets the maximum speed (steps per second).
maxsteps - Gets the ramp steps to maximum speed.
microsteps - Gets the microsteps settings.
The following commands require an argument:
m | stepto <number> - Moves to absolute position (steps).
s | step <number> - Moves relative the number of steps.
t | track <number> - Moves to track number (0-9).
a | moveto <number> - Moves to absolute position (mm).
r | move <number> - Moves the relative distance (mm).
smallstep <number> - Sets the small move distance (mm).
minstep <number> - Sets the min move distance (mm).
retract <number> - Sets the retract distance (mm).
minspeed <number> - Sets the minimum speed (steps per second).
maxspeed <number> - Sets the maximum speed (steps per second).
maxstep <number> - Sets the ramp steps to maximum speed.
microsteps <number> - Sets the microsteps.A set of web pages are available to current stepper status, system info and settings. The home page allows to control the stpper motor using the REST api provided.
All HTML pages use Bootstrap 5 (CSS and JS) files for the display. Those files are provided by https://cdn.jsdelivr.net/npm/[email protected]/dist.
Also an extension to Bootstrap to switch between light and dark theme is used (see https://github.com/coliff/dark-mode-switch).
| Path | Description |
|---|---|
| www/index.html | Returns the main (default) page. |
| www/info.html | Displays the system settings (hardware and network info). |
| www/settings.html | Displays the application settings. |
| www/about.html | A short description of the application and the REST api. |
| www/favicon.ico | File containing the shortcut icons. |
| www/css/dark-mode-switch.css | Bootstrap light switch support. |
| www/js/dark-mode-switch.mini.js | Script for Bootstrap light switch support. |
The web server is used to implement the web interface for the stepper test app. The REST based API is used by the web pages to request settings, current data, and system information. The GET requests can also be used to integrate the sensors into other applications. All provided REST requests returns data in JSON format.
The following list summarizes the conventions adopted by the RESTful implementation.
- GET Retrieves the current status, information, or settings.
- PUT Modifies some data (speed, position, etc.).
- POST Updates settings or execute commands.
- DELETE Not used.
| GET Request | Description |
|---|---|
| /appsettings.json | Downloads the content of the appsettings.json file. |
| /settings | Returns the complete application settings. |
| /system | Returns a set of system information data. |
| /server | The server settings (Http, Telnet). |
| /status | The current stepper state (position, speed etc.). |
| /wifi | The status of the wifi connection (SSID, RSSI etc.). |
| /gpio | The status of the used GPIO pins |
| POST Request | Description |
|---|---|
| /appsettings.json | Uploads an appsettings.json file. |
| /plus | Move a single step forward. |
| /minus | Move a single step backward. |
| /forward | Move a small step (0.1) forward. |
| /backward | Move a small step (0.1) backward. |
| /calibrate | Initiates a calibration routine. |
| /enable | Enables the stepper motor. |
| /disable | Disables the stepper motor. |
| /home | Move ro the home position. |
| /stop | Stops the stepper motor. |
| /release | Relase the stopped motor. |
| /reboot | Reboots the machine. |
| PUT Request | Description |
|---|---|
| /step | Move the number of steps (relative). |
| /move | Move the number of mm (relative). |
| /stepto | Move to absolute position (steps). |
| /moveto | Move to absolute position (mm). |
The Raspberry Pi Pico W and the GPIO pins (output from 'pico' command).
[UART0 TX][I2C0 SDA][SPIO0 RX ][ GP0 ] [01] +--| |--+ [40] [ VBUS ]
[UART0 RX][I2C0 SCL][SPIO0 CSn][ GP1 ] [02] | |___| | [39] [ VSYS ]
[ GND ] [03] | | [38] [ GND ]
[I2C1 SDA][SPIO0 SCK][ GP2 ] [04] | | [37] [ 3V3_EN ]
[I2C1 SCL][SPIO0 TX ][ GP3 ] [05] | | [36] [3V3(OUT)]
[UART1 TX][I2C0 SDA][SPIO0 RX ][ GP4 ] [06] | | [35] [ADC_VREF ]
[UART1 RX][I2C0 SCL][SPIO0 CSn][ GP5 ] [07] | | [34] [ GP28 ][ ADC2 ]
[ GND ] [08] | | [33] [ GND ][ AGND ]
[I2C1 SDA][SPIO0 SCK][ GP6 ] [09] | | [32] [ GP27 ][ ADC1 ][I2C1 SCL]
[I2C1 SCL][SPIO0 TX ][ GP7 ] [10] | | [31] [ GP36 ][ ADC2 ][I2C1 SDA]
[UART1 TX][I2C0 SDA][SPIO1 RX ][ GP8 ] [11] | | [30] [ RUN ]
[UART1 RX][I2C0 SCL][SPIO1 CSn][ GP9 ] [12] | | [29] [ GP22 ]
[ GND ] [13] | | [28] [ GND ]
[I2C1 SDA][SPIO1 SCK][ GP10 ] [14] | | [27] [ GP21 ] [I2C0 SCL]
[I2C1 SCL][SPIO1 TX ][ GP11 ] [15] | | [26] [ GP20 ] [I2C0 SDA]
[UART0 TX][I2C0 SDA][SPIO1 RX ][ GP12 ] [16] | | [25] [ GP19 ][SPIO0 TX ][I2C1 SCL]
[UART0 RX][I2C0 SCL][SPIO1 CSn][ GP13 ] [17] | | [24] [ GP18 ][SPIO0 SCK][I2C1 SDA]
[ GND ] [18] | | [23] [ GND ]
[I2C1 SDA][SPIO1 SCK][ GP14 ] [19] | | [22] [ GP17 ][SPIO0 CSn][I2C0 SCL][UART0 RX]
[I2C1 SCL][SPIO1 TX ][ GP15 ] [20] |_________| [21] [ GP16 ][SPIO0 RX ][I2C0 SDA][UART0 TX]
[ OUTPUT ][ PUL ][ GP0 ] [01] +--| |--+ [40] [ VBUS ]
[ OUTPUT ][ DIR ][ GP1 ] [02] | |___| | [39] [ VSYS ]
[ GND ] [03] | | [38] [ GND ]
[ OUTPUT ][ ENA ][ GP2 ] [04] | | [37] [ 3V3_EN ]
[ OUTPUT ][ Led 1 ][ GP3 ] [05] | | [36] [3V3(OUT)]
[ OUTPUT ][ Led 2 ][ GP4 ] [06] | | [35] [ADC_VREF]
[ OUTPUT ][ Led 3 ][ GP5 ] [07] | | [34] [ GP28 ]
[ GND ] [08] | | [33] [ GND ]
[ INPUT ][ SW 1 ][ GP6 ] [09] | | [32] [ GP27 ]
[ INPUT ][ SW 2 ][ GP7 ] [10] | | [31] [ GP36 ]
[ INPUT ][ SW 3 ][ GP8 ] [11] | | [30] [ RUN ]
[ GP9 ] [12] | | [29] [ GP22 ]
[ GND ] [13] | | [28] [ GND ]
[ GP10 ] [14] | | [27] [ GP21 ]
[ GP11 ] [15] | | [26] [ GP20 ]
[ GP12 ] [16] | | [25] [ GP19 ]
[ GP13 ] [17] | | [24] [ GP18 ]
[ GND ] [18] | | [23] [ GND ]
[ GP14 ] [19] | | [22] [ GP17 ]
[ GP15 ] [20] |_________| [21] [ GP16 ]
In order to drive the stepper motor with a certain speed (steps per second), the correct number of output pulses per second have to be generated.
A global periodic timer running at 100 kHz is used to generate pulses for the stepper motor driver unit. The timer callback function is therefore called 100000 times a second, or every 10 microseconds.
An internal step counter is used to keep track of the required steps to reach a specified target. A second internal counter is used to determine the delay between pulses (steps) depending on the specified speed.
The pulsewidth is fixed at 10 microseconds (the output is set high at the first call, and set low at the second call). The second counter is increased until the number of required calls (number of intervals) is reached.
The total time required for the number of steps needed to move a specified distance is the number of steps times the delay between the steps (pulses).
Ramping (accelerating and decelerating) is done by changing the time between the steps (pulses) from a minimum speed to a maximum speed and back again.
Since the number of intervals has to be an integer number, the set speed will be only approximately correct. However, the stepper driver is moving for the required number of steps with the set speed. The maximum speed is a delay of 10 us (2 intervals) resulting in a 20 us period or 50 kHz.
For a typical stepper motor driver with 200 steps per revolution and a linear actuator with a lead screw providing 8 mm travel distance per revolution, this results in 40 steps per mm. When microstepping is used, the number of steps / mm is increased acordingly. The attainable speed for a stepper motor is typically ca. 1000 rpm. With higher speed, the torque is considerable decreased, and the motor has to ramp up the speed slowly. Assuming a maximum frequency of 50 kHz, the resulting maximum RPM is as follows:
8.00 mm per rotation
200 steps per rotation
100000 timer frequency (100 kHz)
25000 max steps per second (4 cycles)
(steps/rotation) = microsteps*(steps/rotation)
(steps/mm) = (steps/rotation)/(distance/rotation)
(max rpm) = 60*(max steps/second)/(steps/rotation)
(mm/sec) = (distance/rotation)*(max rpm)/60
| microsteps | steps/rotation | steps/mm | max rpm | mm/sec |
|---|---|---|---|---|
| 1 | 200 | 25 | 7500.0 | 1000.0 |
| 2 | 400 | 50 | 3750.0 | 500.0 |
| 4 | 800 | 100 | 1875.0 | 250.0 |
| 5 | 1000 | 125 | 1500.0 | 200.0 |
| 8 | 1600 | 200 | 937.5 | 125.0 |
| 10 | 2000 | 250 | 750.0 | 100.0 |
| 16 | 3200 | 400 | 468.8 | 62.5 |
| 20 | 4000 | 500 | 375.0 | 50.0 |
| 25 | 5000 | 625 | 300.0 | 40.0 |
| 32 | 6400 | 800 | 234.4 | 31.3 |
| 40 | 8000 | 1000 | 187.5 | 25.0 |
| 50 | 10000 | 1250 | 150.0 | 20.0 |
| 64 | 12800 | 1600 | 117.2 | 15.6 |
| 100 | 20000 | 2500 | 75.0 | 10.0 |
| 125 | 25000 | 3125 | 60.0 | 8.0 |
| 128 | 25600 | 3200 | 58.6 | 7.8 |
The typical speed used in this application is in the range of 1000 to 5000 steps/sec or 2.5 mm/sec to 12.5 mm/sec. Higher microstepping values could be used, but the maximum speed decreases accordingly.