MicroPython API

MicroPython lets you prototype and build your applications quickly without having to dive into any low level programming. With a few lines of Python, you can draw to the display, access the camera, and offload processing to the FPGA. Of course you get all the other benefits of Python too. Best of all, it’s completely wireless, and you can access the Python REPL fully over Bluetooth.

The MicroPython firmware for Monocle is a customized firmware which is largely based on the upstream MicroPython project. Thanks to the large MicroPython community, we’re always updating to new features as they come out on the upstream project.

A subset of the standard MicroPython libraries are currently supported, with more periodically being added. Additionally, some extra modules are included which let you easily interact with the Monocle hardware. Be sure to check out the MicroPython docs site, as well as the docs here to familiarize yourself with all the features.

Getting start

Brilliant AR Studio for VSCode

Get started by trying out the VSCode extension on PC or MacOS. Once installed:

• Initialize a new project using the command Ctrl-Shift-P (Cmd-Shift-P on MacOS) → Brilliant AR Studio: Initialize new project folder.
• Then connect to Monocle by brining it close and running the command Ctrl-Shift-P → Brilliant AR Studio: Connect.

• Copy paste the example below into main.py and save the file.

    import touch
    import display
  
    def change_text(button):
        new_text = display.Text(f"Button {button} touched!", 0, 0, display.WHITE)
        display.show(new_text)
  
    touch.callback(touch.BOTH, change_text)
  
    initial_text = display.Text("Tap a touch button", 0, 0, display.WHITE)
    display.show(initial_text)
  

• After a few moments, you should be able to touch each of the touch pads on Monocle, and see the display update.

WebREPL Console

Monocle also supports bare scripting from a custom app. The Web Bluetooth REPL is a good starting point for debugging and using as a template for building your own web apps. Try it from Google Chrome on your PC, Mac, Android, or a Web Bluetooth compatible web browser on your iOS device such as Bluefy.

Check out the full instructions and the source code here.

Library reference

MicroPython for Monocle is always being updated so be sure to check back frequently. The ❌ icon signifies a feature which is not implemented yet, but is planned.

1. builtins
2. device – Monocle specific
3. display – Monocle specific
4. camera – Monocle specific
5. microphone – Monocle specific
6. touch – Monocle specific
7. led – Monocle specific
8. fpga – Monocle specific
9. bluetooth - Monocle specific
10. time – Monocle specific
11. update - Monocle specific
12. gc
13. math
14. micropython
15. uarray
16. uasyncio
17. ubinascii
18. ucollections
19. uerrno
20. uhashlib
21. uio
22. ujson
23. uos
24. urandom
25. ure
26. uselect
27. ustruct
28. usys

builtins

Standard MicroPython built in functions are supported.

Example

import builtins
help(builtins) # Lists all of the built-in MicroPython functions

device – Monocle specific

The device class contains general information about the Monocle’s hardware and firmware.

Example

import device
device.VERSION # Prints the device firmware version
device.battery_level() # Returns the current battery level as a percentage

display – Monocle specific

The display module allows for drawing to the micro OLED display.

This shows, for a given coordinate (x,y) used as reference, where the text will be placed:

import display

# Place some text in the middle of the screen with a line underneath
text = display.Text('Hello world', 320, 200, display.WHITE, justify=display.MIDDLE_CENTER)
line = display.Line(175, 230, 465, 230, display.WHITE)
display.show(text, line)

# Group the line and the text together to change the color of both at the same time
group = [text, line]
display.color(group, display.GREEN)
display.show(group)

# Move the line above the text, and print everything again
line.move(0, -75)
display.show(group)

# Create a white polygon with a red outline and print everything again
poly = display.Polygon([0, 0, 639, 399, 0, 399], display.WHITE)
outline = display.Polyline([0, 0, 639, 399, 0, 399, 0, 0], display.RED)
display.show(text, line, outline, poly)

camera – Monocle specific

The camera module allows for capturing images and transferring them to another device over Bluetooth.

Example

import camera
camera.overlay(True) # Turns on mirroring from the camera to the display
camera.overlay(False) # Turns off mirroring from the camera to the display

microphone – Monocle specific

The microphone module allows for capturing audio and streaming it to another device over Bluetooth.

touch – Monocle specific

The touch module allows for reacting to touch events from the capacitive touch pads on Monocle.

Example

import touch

# Define the touch callback function which is triggered upon a touch event
def fn(arg):
    if arg == touch.A:
        print("button A pressed!")
    if arg == touch.B:
        print("button B pressed!")

touch.callback(touch.BOTH, fn) # Attaches the callback to the both buttons
touch.callback(touch.A, fn) # Attaches the callback to an individual button

led – Monocle specific

The LED module contains functions to control the red and green LED on the front of Monocle.

Example

import led
led.on(led.GREEN) # Turns on the green LED
led.on('GREEN') # Also turns on the green LED
led.off(led.GREEN) # Turns off the green LED
led.on(led.RED) # Turns on the red LED
led.off(led.RED) # Turns off the red LED

fpga – Monocle specific

The FPGA module allows for communicating with the FPGA over the internal SPI bus.

Example

import fpga
fpga.read(0x1234, 5) # Reads 5 bytes from some FPGA register (0x1234 in this case)
fpga.write(0x1234, b'\x01\x02\x03') # Writes three bytes (1, 2, 3) to the FPGA register 0x1234
fpga.write(0x1234, b'hello fpga') # Writes the byte string 'hello fpga' to the FPGA register
fpga.write(0x1234, b'') # Doesn't write anything specific, but acts as a command or trigger

bluetooth - Monocle specific

The bluetooth module can be used to transfer byte data between Monocle and the host Bluetooth device. Bytes can contain any arbitrary data, and avoids having to pollute the REPL interface with printing data out as strings. The raw data service is used for all communications under the bluetooth module.

Example

import bluetooth
bluetooth.connected() # Returns True if the Bluetooth is connected. Always true when using the REPL, but useful for saved scripts
len = bluetooth.max_length() # Returns the maximum payload size we can send in one go

str = "hello world"
bluetooth.send(str[:len]) # Sends the string 'hello world' to the host. Limited by the maximum payload size

# Define a callback function which is triggered upon reception of Bluetooth data from the host
def fn(bytes):
    print(bytes)

bluetooth.receive_callback(fn) # Attaches the above function to the receive callback

time – Monocle specific

The time module allows for getting/setting the time and date as well as adding delays into your programs.

Example

import utime
time.sleep(1.5) # Sleeps for 1.5 seconds
time.sleep_ms(100) # Sleeps for 500ms
time.time(1681236168) # Sets the device system time using UTC timestamp
time.time() # Returns the current time (as a UTC timestamp), based on the system time
time.now() # Returns the current time as a human readable dictionary

update - Monocle specific

The update module allows for firmware upgrades of the MicroPython firmware, as well as the FPGA application over bluetooth. This library use used automatically by the Brilliant REPL for firmware updates. You generally shouldn’t need to call these manually, unless you’re implementing your own update process.

Example

import update
update.micropython() # Reboots the device into update mode for updating the MicroPython firmware

gc

Standard MicroPython garbage collection is supported.

Example

import gc

# Shows the current memory usage as a percentage
mem_used = gc.mem_alloc() / (gc.mem_alloc() + gc.mem_free())
print('{:d}%'.format(round(mem_used * 100)))

# Manually runs the garbage collector
gc.collect()

math

Standard MicroPython math functions are supported.

micropython

Standard MicroPython internals are supported.

uarray

Standard MicroPython arrays are supported.

uasyncio

Standard MicroPython asynchronous scheduling is supported.

ubinascii

Standard MicroPython binary/ASCII conversions are supported.

ucollections

Standard MicroPython collection and container types are supported.

uerrno

Standard MicroPython system error codes are supported.

uhashlib

Standard MicroPython hashing algorithms are supported.

uio

Standard MicroPython IO streams are supported.

ujson

Standard MicroPython JSON handling is supported.

uos

Standard MicroPython operating system services for file handling are supported.

urandom

Standard MicroPython random number generation is supported.

ure

Standard MicroPython regular expressions are supported.

uselect

Standard MicroPython stream event waiting is supported.

ustruct

Standard MicroPython struct primitives are supported.

usys

Standard MicroPython system specific functions are supported.

Under the hood

This section describes how data is transferred to and from Monocle over Bluetooth.

For testing everything Bluetooth related, try our the nRF Connect App, for desktop, Android, or iOS.

Communication

All MicroPython communication, i.e. the REPL interface, is accessed via a single Bluetooth Service containing two Characteristics.

• Serial service UUID: 6e400001-b5a3-f393-e0a9-e50e24dcca9e
• Serial RX characteristic UUID: 6e400002-b5a3-f393-e0a9-e50e24dcca9e
• Serial TX characteristic UUID: 6e400003-b5a3-f393-e0a9-e50e24dcca9e

The RX characteristic is write only, and transports serial string data from the central BLE device to Monocle. The TX characteristic is notification only and delivers messages back from Monocle, to the central BLE device.

Each characteristic transports string data of any length up to the negotiated MTU size - 3 bytes. Longer strings must be chopped up and will be automatically rejoined on the receiving side by Monocle. Likewise if Monocle wishes to send longer responses than can fit into a single MTU payload, the data will arrive sequentially, and can be concatenated by the central Bluetooth app. The diagram below describes how communication operates between Monocle and a central device.

A secondary Bluetooth Service, again containing two Characteristics, is used to transport raw data such as image, audio and firmware update data. The mechanism for the raw data service is similar to the serial data service, aside from the fact that null or 0 characters may also be included within the payload.

• Raw data service UUID: e5700001-7bac-429a-b4ce-57ff900f479d
• Raw data RX Characteristic UUID: e5700002-7bac-429a-b4ce-57ff900f479d
• Raw data TX Characteristic UUID: e5700003-7bac-429a-b4ce-57ff900f479d

Raw data transfer may often be bigger than a single MTU payload. Similarly to the serial data, it may need to be broken up into pieces. To help reconstruct the packets sent or received by Monocle, a flag is present at the start of each payload to determine if it’s either a starting payload, middle payload, end payload, or a small single buffer payload. The exact mechanisms for different types of data transfer are outlined below.

Downloading media

Media files such as audio and images may be downloaded from the Monocle using the raw data service mentioned in the Communication section. Files may also be sent asynchronously by Monocle when they are ready.

Due to the small payload size of Bluetooth packets, the file may be spit into many chunks and need to be recombined by the receiving central device. A flag at the start of each payload indicates if it is the START, MIDDLE or END of the file. A very small file may also be transferred using the SMALL flag.

The first payload includes metadata about the file such as the filename (with a relevant file extension) and the file size. The sequence diagram below describes how a file is broken into several parts and the data can be recombined to construct the full file:

Firmware updates

Within the Web REPL, firmware updates should show up automatically, and you’ll be prompted to update. If it doesn’t work. You can follow these steps:

1. Make sure you’re using a Bluetooth enabled web browser such as Google Chrome on desktop, Android Chrome, or Bluefy on iOS.
2. Navigate to the repl at repl.brilliant.xyz
3. Take monocle out of the case. It should turn on.
4. Press any key in the repl to connect.
5. Select monocle from the Bluetooth menu that appears.

6. An update notification should appear at the bottom. Click it.

   If it doesn’t show up, you can force an update using the commands:

    import update;update.micropython()
   

7. Monocle will disconnect, and you’ll see a message to reconnect again.
8. Press any key to reconnect and select DFUTarg from the Bluetooth menu.
9. The update should start, and you’ll see the progress.
10. If anything goes wrong, simply try again.

Under the hood, the update .zip file is obtained from the releases page of the monocle-micropython repository. After that Monocle is rebooted into device firmware update (DFU) mode where the Nordic DFU service handles the transfer of the file data. To read how the DFU mechanism works, you can check the Nordic documentation here.

For testing everything Bluetooth related, try our the nRF Connect App, for desktop, Android, or iOS.

FPGA application updates

FPGA application updates are automatically updated when using the Brilliant WebREPL.

For simplicity, the WebREPL encodes the application binary file to base-64 format, and simply sends the data over the raw REPL. The entire process is shown below.

import device
import update
import ubinascii

# Erases the entire application
update.Fpga.erase()

# Send exactly 444430 bytes. Each write appends to the already written data
# There's no limitation on how many bytes you can send, but it should be
# tuned to match the host MTU length for a faster upload speed
update.Fpga.write(ubinascii.a2b_base64(b'TWFueSBoYW5kcyBtYWt...lIGxpZ2h0IHdvcmsu'))
...
update.Fpga.write(ubinascii.a2b_base64(b'yBtYWtTWFueSBoYW5kc...cmslIGxpZIHd2h0vu'))

# Write the special "done" flag at the end of the file
update.Fpga.write(b'done')

device.reset()