The Servo Board can be used to control up to 12 RC servos. Many devices are available that can be controlled as servos, such as RC motor speed controllers, and these can also be used with the board.
These are split into 2 groups:
- 0-7 have a fixed 5.5V output, supplied from the onboard regulator
- 8-11 have their output voltage supplied from the AUX header and can be provided up to 12 volts
Using a posix system, you require make, the arm-none-eabi toolchain and git.
Before attempting to build anything initialise all the submodules.
$ git submodule update --init --recursiveTo build the main binary, run:
$ makeThe binary will then be at src/main.bin.
This will also build the library libopencm3 the first time you run it.
This can be flashed to an attached servo board that has a bootloader using:
$ make -C src dfuTo use the dfu command you need to install dfu-utils. This is a cross-platform utility.
To build the bootloader, run:
$ make -C bootloaderThe bootloader binary will then be at bootloader/usb_dfu.bin
There are 14 LEDs accessible from the firmware, 12 associated with servo outputs and 2 general status LEDs. The 12 associated with servo outputs are lit when the corresponding output is enabled. The blue status LED is lit once the MCU has initialised. The red status LED is lit when there is an I2C communication error, likely due to missing 12V power.
The Vendor ID is 1bda (University of Southampton) and the product ID
is 0011.
The Servo Board is controlled over USB serial, each command is its own line.
Since the serial port is virtual, the baudrate is unused and can be set to any value.
| Action | Description | Command | Parameter Description | Return | Return Parameters |
|---|---|---|---|---|---|
| Identify | Get the board type and version | *IDN? | - | Student Robotics:SBv4B:<asset tag>:<software version> | <asset tag> <software version> |
| Status | Get board status | *STATUS? | - | <Watchdog fail>:<pgood> | <Watchdog fail> - watchdog timeout, int, 0-1 <pgood> - power good, int, 0-1 |
| Reset | Reset board to safe startup state - Disable all servos - Reset the lights |
*RESET | - | ACK | - |
| Disable output | Disable a servo output,set to 0 pulse width | SERVO:<n>:DISABLE | <n> servo number, int, 0-11 | ACK | - |
| Set position | Set the position of a servo | SERVO:<n>:SET:<value> | <n> servo number, int, 0-11 <value> servo duty time, us, 500-4000 |
ACK | - |
| Get position | Get the current position setting for a servo | SERVO:<n>:GET? | <n> servo number, int, 0-11 | <value> | <value> servo duty time, us, 500-4000 |
| Read servo current | Get total 5V current draw | SERVO:I? | - | <current> | <current> - current, int, measured in mA |
| Read servo voltage | Get 5V SMPS output voltage | SERVO:V? | - | <voltage> | <voltage> - voltage, int, measured in mV |
| Debug servo values | Print the internal values for servo pulses | *DBG:SERVO:<phase> | <phase> - Servo output phase number, int, 0-3 | <phase data> | <phase data> - Raw servo phase values |
If you are connecting the Servo Board to a Linux computer with udev, the following rule can be added in order to access the Servo Board interface without root privileges:
SUBSYSTEM=="usb", ATTRS{idVendor}=="1bda", ATTRS{idProduct}=="0011", GROUP="plugdev", MODE="0666"
It should be noted that plugdev can be changed to any Unix group of
your preference.
This should only be necessary when trying to access the bootloader.
You can access the schematics and source code of the hardware in the following places.