Week 6: Embedded Programming

This week we worked on embedded programming. We were given a Seeed XIAO RP2040 board from Seeed studios. Overview: https://wiki.seeedstudio.com/XIAO-RP2040/

Group Assignment

The page describing the group assignment for this week (demonstrate and compare the toolchains and development workflows or alternative embedded architectures) can be found here.

Soldering

The useful tutorial to soldering headers here.

I did solder some stuff before, but I am still need more practising. Should’ve watched more tutorials. I like that there are quite a few tools in the lab (such as flux pen and desoldering braid), was happy to get to try all of them.


Figure 2: My workbench setup		Figure 3: The Flux pen

Before I started soldering, I turned on the fan. After a bit, I had a first attempt at soldering the headers, but it turned out not ideal.

**Figure 4:** Messed up solder where two of the rightmost pins are connected together

Therefore, (with Yu-Hans help) I used the disordering braid to remove the excessive tin.

After this I managed to solder the pins (although not beautifully). I now understand that the tin is supposed to cover the “golden” area where the pins are, so they are securely in place. To check that there is no short circuit, I used the voltmeter (the resistance setup) to check all the neighboring pins.


Figure 6: Using voltmeter to check for short circuit		Figure 7: Final look on my board after headers are attached

Programming

I wanted to use Arduino to program the board, however for some reason on my computer I couldn’t find the Raspberry Pi Pico/RP2040 - I will solve this problem later, but for now let’s try using the MicroPython and the Thonny IDE.thonny

Installing Thonny:

brew install --cask thonny

I haven’t used MicroPython with a board yet, so it’s a nice learning experience. I am not sure if I would use it in production as it is still Python - too big for some microcontrollers, somewhat clumsy and not real time. But its nice for testing, and I do believe it is easier to program. Documentation can be found here.

The initial setup was a bit tricky, and can be found here. Interesting steps were that the board should be booting when connecting to the computer, and then how MicroPython is installed to the board.

First program

To showcase that the board works, and it’s correctly set up, I tried to run one of the default programs (something like blink in the Arduino library).

# this is a default code to test the connection with RP2040
from ws2812 import WS2812
import utime
import machine
power = machine.Pin(11,machine.Pin.OUT)
power.value(1)
BLACK = (0, 0, 0)
RED = (255, 0, 0)
YELLOW = (255, 150, 0)
GREEN = (0, 255, 0)
CYAN = (0, 255, 255)
BLUE = (0, 0, 255)
PURPLE = (180, 0, 255)
WHITE = (255, 255, 255)
COLORS = (BLACK, RED, YELLOW, GREEN, CYAN, BLUE, PURPLE, WHITE)

led = WS2812(12,1)#WS2812(pin_num,led_count)

while True:
    print("Beautiful color")
    for color in COLORS: 
        led.pixels_fill(color)
        led.pixels_show()
        utime.sleep(0.2)

More sophisticated program

I made a program that the colour changes when you press the button.

from ws2812 import WS2812
import utime
import machine

power = machine.Pin(11,machine.Pin.OUT)
power.value(1)
button = machine.Pin(1, machine.Pin.IN, machine.Pin.PULL_UP)
RED = (255, 0, 0)
YELLOW = (255, 150, 0)
GREEN = (0, 255, 0)
CYAN = (0, 255, 255)
BLUE = (0, 0, 255)
PURPLE = (180, 0, 255)
WHITE = (255, 255, 255)
COLORS = (RED, YELLOW, GREEN, CYAN, BLUE, PURPLE, WHITE)
 
led = WS2812(12,1)#WS2812(pin_num,led_count)
i = 0
color = WHITE
 
while True:
    if not button.value():
        print('Button pressed!')
        led.pixels_fill(color)
        led.pixels_show()
        color = COLORS[i%7]
        i += 1
        utime.sleep(0.5)

Serial connection

As mentioned, I had problems with Arduino. It turns out it was because I forgot to add Additional Boards Manager URLs in Preferences (as shown in this tutorial). Now, using Arduino interface, I made a simple command like code where the commands I was writing on the computer where changing the LED color on the XIAO board to some pre-defined colors.

Video of the code execution:

#include <Adafruit_NeoPixel.h> 
int powPin = NEOPIXEL_POWER; 
int neoPin = PIN_NEOPIXEL; 

Adafruit_NeoPixel pix(1, neoPin, NEO_GRB + NEO_KHZ800); 

void setup() {
  pix.begin(); 
  pinMode(powPin, OUTPUT);
  digitalWrite(powPin, HIGH);
  Serial.begin(19200); 
 } 
 
 void loop() {
  while(Serial.available()>0){
    char message = Serial.read();
    Serial.print("Received: ");
    Serial.println(message);
    
    if (message == 'r'){
      pix.setPixelColor(0, pix.Color(255, 0, 0));
      pix.show();
    } else {
      if (message == 'y'){
        pix.setPixelColor(0, pix.Color(255, 150, 0));
        pix. show();
      } else {
        if (message == 'g'){
          pix.setPixelColor(0, pix.Color(0, 255, 0));
          pix.show();
        }
     }
    }
    delay(200);
  }
 }

A more advanced example where the board is interacting with an application through the REST API is covered in Week 14 - Interface and Application programming.

Fab Academy portfolio Sara Kutkova