polyglot-turtle 0.3.1

A python driver for the polyglot-turtle firmware

python-polyglot-turtle

This repository contains a python library for communicating with the polyglot-turtle firmware. It has been tested to work on Windows, Mac and Linux.

To install or upgrade, run

pip install --upgrade polyglot-turtle

or

python -m pip install --upgrade polyglot-turtle

Only python 3.6+ is supported. This driver does not expose any USB-to-serial functionality, for that you should use something like pyserial.

Extra install instructions for Linux users

This library depends on cython-hidapi which requires you to install some extra binary dependencies. On Ubuntu (tested on 18.04 and 20.04), you can install these dependencies using the following command:

sudo apt-get install python3-dev libusb-1.0-0-dev libudev-dev

By default, Linux does not allow access to USB or HID devices for a non-root user. To give access to your own user is simple. First, in /etc/udev/rules.d, create a new file called 99-polyglot-turtle.rules and paste the following two lines in:

SUBSYSTEM=="usb", ATTRS{idVendor}=="04d8", ATTRS{idProduct}=="eb74", MODE="0660", GROUP="plugdev", TAG+="uaccess", TAG+="udev-acl", ENV{ID_MM_DEVICE_IGNORE}="1"
KERNEL=="hidraw*", ATTRS{idVendor}=="04d8", ATTRS{idProduct}=="eb74", MODE="0660", GROUP="plugdev", TAG+="uaccess", TAG+="udev-acl"

This will give access to any user in the plugdev group. Now, just add yourself to the group:

sudo usermod -a -G plugdev <your username>

(you need to replace <your username> with your actual username on your computer).

Once this is done, reboot and everything should work.

Usage

Almost all code using this library will need two lines:

from polyglot_turtle import PolyglotTurtleXiao

pt = PolyglotTurtleXiao()

The first line imports the main class from the library, and the second line connects to the device. After that, you simply use the pt object to interact with your device.

You can connect to a specific device using its serial number if more than one is present:

from polyglot_turtle import PolyglotTurtleXiao

pt = PolyglotTurtleXiao(serial_number="9B1EC96D5053574C342E3120FF02110D")

All devices have a unique serial number that is associated with the USB device. You can find this number in Windows using Device Manager, in Mac OS using System Report, and in Linux using lsusb. You can also use this library to return a list of the serial numbers of all connected devices:

from polyglot_turtle import list_polyglot_turtle_xiao_devices

print(list_polyglot_turtle_xiao_devices())
# prints all serial numbers, for example ['9B1EC96D5053574C342E3120FF02110D']

GPIO

There are 4 GPIO pins on the polyglot-turtle-xiao numbered 0-3. All four of these pins can be used as a digital input or output by setting the pin direction:

from polyglot_turtle import PolyglotTurtleXiao, PinDirection

pt = PolyglotTurtleXiao()

pt.gpio_set_direction(0, PinDirection.OUTPUT)  # set GPIO 0 to output
pt.gpio_set_direction(1, PinDirection.INPUT)  # set GPIO 1 to input

To read from an input or write to an output, use the gpio_get_level and gpio_set_level functions respectively:

from polyglot_turtle import PolyglotTurtleXiao, PinDirection

pt = PolyglotTurtleXiao()

pt.gpio_set_direction(0, PinDirection.OUTPUT)  # set GPIO0 to output
pt.gpio_set_level(0, True)  # set GPIO 0 to high
pt.gpio_set_level(0, False)  # set GPIO 0 to low

pt.gpio_set_direction(1, PinDirection.INPUT)  # set GPIO1 to input
print(pt.gpio_get_level(1))  # prints "True" or "False" depending on the state of GPIO1

When using a pin as an input, you can additionally enable a weak internal pullup or pulldown resistor:

from polyglot_turtle import PolyglotTurtleXiao, PinDirection, PinPullMode

pt = PolyglotTurtleXiao()
pt.gpio_set_direction(1, PinDirection.INPUT)  # set GPIO1 to input

pt.gpio_set_pull(1, PinPullMode.PULL_UP)  # enable the pullup
pt.gpio_set_pull(1, PinPullMode.PULL_DOWN)  # enable the pulldown
pt.gpio_set_pull(1, PinPullMode.NONE)  # leave the input floating

SPI

To use the Serial Peripheral Interface (SPI), connect one of the GPIO pins to the CS pin of your target device, and otherwise connect MISO, MOSI and SCK as usual.

The polyglot-turtle firmware supports a single SPI operation, called 'exchange'. This can be used to interact with any SPI device, and even some non-SPI devices too! In an exchange operation, the polyglot-turtle firmware will write all of the bytes provided to the target device, and return all of the bytes read back from the device. As SPI requires the device to shift out one byte for every byte shifted in, you will receive the same number of bytes that was written.

An SPI exchange requires you to send the following parameters to the device:

• The data to send
• The SPI clock rate (100kHz to 10MHz)
• The SPI mode (default 0 if not specified)
• The transaction timeout in milliseconds, after which it will be assumed that the command execution failed (default 50ms if not specified)
• the CS pin to set low and then high automatically (default is to not change any GPIO pins unless one is specified)

from polyglot_turtle import PolyglotTurtleXiao, PinDirection

pt = PolyglotTurtleXiao()
pt.gpio_set_direction(0, PinDirection.OUTPUT)  # GPIO0 will be used as the CS pin
pt.gpio_set_level(0, True)  # set the CS pin to high by default

# perform a transaction with manual CS control
pt.gpio_set_level(0, False)  # set CS low
print(pt.spi_exchange(b"\x01\x02\x03", clock_rate=100000, mode=0))
pt.gpio_set_level(0, True)  # set CS high

# perform the same transaction but with automatic CS control
print(pt.spi_exchange(b"\x01\x02\x03", clock_rate=100000, mode=0, cs_pin=0))

# perform the same automatic CS transaction but with a 1 second timeout
print(pt.spi_exchange(b"\x01\x02\x03", clock_rate=100000, mode=0, cs_pin=0, transaction_timeout_ms=1000))

I2C

Almost all Inter-Integrated Circuit (I2C) transactions can be broken down into combinations of three operations:

1. (Write operation) START, Address + Write, write N bytes, STOP
2. (Read operation) START, Address + Read, read N bytes, STOP
3. (Write-then-read operation) START, Address + Write, write N bytes, REPEATED START, Address + Read, read N bytes, STOP

The polyglot-turtle firmware supports all three of these operations using a single function, i2c_exchange. This function takes the following arguments:

• The target device address (right aligned, between 0 and 127 inclusive)
• The data to write (default is empty)
• The number of bytes to read (default is 0)
• The I2C bus clock rate (one of three specific values)
• The transaction timeout in milliseconds, after which it will be assumed that the command execution failed (default 50ms if not specified)

The type of operation is selected simply by the number of bytes provided to write, and the number of bytes requested to read.

1. (Write operation) If there are bytes to write and the number of bytes to read is 0
2. (Read operation) If there are no bytes to write and the number of bytes to read is > 0
3. (Write-then-read operation) If there are both bytes to write and the number of bytes to read is > 0

See below for some examples:

from polyglot_turtle import PolyglotTurtleXiao, I2cClockRate

pt = PolyglotTurtleXiao()
address = 0x32  # device we are talking to is at address 0x32

# perform a write transction with the bytes 0x12 0x34
pt.i2c_exchange(address, write_data=b"\x12\x34", clock_rate=I2cClockRate.STANDARD)  

# perform a read operation and read 4 bytes
pt.i2c_exchange(address, read_size=4, clock_rate=I2cClockRate.STANDARD)  

# perform a write-then-read operation where 0x12 0x34 is written and then 4 bytes are read back
pt.i2c_exchange(address, write_data=b"\x12\x34", read_size=4, clock_rate=I2cClockRate.STANDARD)  

Since the I2C standard only allows three specific clock rates, the polyglot-turtle firmware also only supports these three speeds:

• STANDARD: 100kHz
• FAST: 400kHz
• FAST_PLUS: 1MHz

PWM

Pulse Width Modulation (PWM) signals can be used for driving motors and dimming LEDs. PWM can be enabled on GPIO pins if it is supported (see device pinout for more information).

To use the PWM functionality, one must first call the function pwm_get_info. This will return an array containing information about the PWM capabilities of the device:

1. The first element of the array is the maximum value the internal counter can count up to
2. The second element is the maximum value for the compare threshold
3. The final element is an array of all possible counter clock rates. The fastest clock rate will be element 0, with any others sorted in order of decreasing frequency.

To instruct the device to output a PWM signal, you need to pass the following arguments to pwm_set:

• the gpio pin number to use for the output
• the counter period
• the counter duty cycle
• optionally, the clock rate index (the index of the clock rate you wish to use from the clock rate array)

Note that all of these values should be integers, not floating point/decimal numbers.

The counter model used by the polyglot-turtle device is fairly simple. The counter will count from 0 to the counter period value at the specified clock rate. When the counter period value is reached, the counter will reset to 0 and begin counting up again. The PWM output is controlled by the comparison between the current counter value and the supplied duty cycle value:

1. if the counter < duty cycle, set output high
2. else set output low

For an example of using this functionality, take a look at the pwm_servo.py example in this repository. This example generates a PWM signal with a 20ms period and a 1-2ms varying duty cycle to drive a servo motor.

DAC

A Digital to Analog Converter (DAC) transforms a number into a voltage across a specific voltage range. To use the DAC, one can request the range information about the DAC, and then use that to instruct the DAC to output a specific voltage.

from polyglot_turtle import PolyglotTurtleXiao

pt = PolyglotTurtleXiao()
maximum_dac_value, maximum_dac_voltage = pt.dac_get_info()

voltage_to_output = 1.2  # volts
dac_value = int(voltage_to_output * (maximum_dac_value+1)/maximum_dac_voltage)

pt.dac_set(0, dac_value)

The dac_get_info function returns two numbers:

1. The maximum value the DAC will accept (2^(N-1) for an N bit DAC)
2. The maximum voltage that the DAC is able to output

Using those two pieces of information, one can calculate the DAC value to use to generate a specific output voltage using the dac_set function. The first argument of the dac_set function is the GPIO number of the pin to use, and the second argument is the DAC value as an integer. Note that the result of any calculations must be converted to an integer before passing it to the dac_set function.

Please note that the output will be limited by the resolution and performance of the DAC in the device.

ADC

The Analog to Digital Converter (ADC) functionality is used to read an analog voltage and report the value as a number. To use it, pass the GPIO number for the pin you wish to read the voltage on to the adc_get function:

from polyglot_turtle import PolyglotTurtleXiao

pt = PolyglotTurtleXiao()
reading, max_reading, max_voltage = pt.adc_get(1)

# calculate the actual voltage at the pin
voltage_reading = reading * max_voltage / (max_reading+1)

This function returns three numbers:

1. The ADC conversion result as an integer
2. The maximum possible reading that the ADC could return as an integer (typically 2^(N-1) for an N bit ADC)
3. The voltage which corresponds to the maximum ADC reading

You can then calculate the actual voltage reading using the formula in the example above. Note that the reading will be limited by the resolution and performance of the ADC in the device.

The file adc_example.py shows a combination of using the DAC to generate a voltage, and then a conversion of that voltage back into a number using the ADC.

Programming AVR microcontrollers (experimental)

It is possible to use python-polyglot-turtle to program AVR microcontrollers via the standard ISP interface. However, since there are no hardware protection circuits on the polyglot-turtle, there are a few limitations you need to be aware of:

1. You should only use this functionality if the SPI port on the AVR is unused by your firmware (the MISO, MOSI and SCK pins).
2. There should be nothing already connected to the RESET pin on the AVR except for a pull-up resistor.
3. The AVR must be powered by a 3.3V supply

If your circuit meets all of these requirements, you can program your microcontroller directly with the polyglot-turtle.

Software setup

This functionality relies on the open source tool avrdude to generate the flashing instructions for the polyglot-turtle to use.

If you are on Windows, you can install a special package with pip that allows python to access avrdude:

python -m pip install --upgrade avrdude-windows

On Mac you can use the Homebrew package manager:

brew install avrdude

If you are on Linux, you can simply use your package manager to install this tool:

sudo apt install avrdude

Flashing your firmware

Please see the avr_program.py example. This writes the firmware file test.hex to an atmega328p.

Further examples

There are some simple examples in the git repository you can look at for more information.