pico example: test on a real board and add documentation

Author: dgoffredo

sample-implementations/RaspberryPi_Pico/README.md

@@ -0,0 +1,39 @@
+SCD4x on the Raspberry Pi Pico
+==============================
+<img alt="Pico W with an SCD41 connected" src="hardware.jpg" height="400"/>
+
+In this example, an SCD41 is connected to a Raspberry Pi Pico W on GPIO pins 16
+(I2C0 SDA) and 17 (I2C0 SCL). The same code will work for any variant of the
+Pico.
+
+The following shell session is from an Ubuntu machine that had the Pico plugged
+in to USB in boot select mode.
+
+```console
+$ ls
+CMakeLists.txt  hardware.jpg  main.c  README.md  sensirion_i2c_hal.c
+
+$ mkdir build
+
+$ cd build
+
+$ cmake -DPICO_SDK_PATH=$HOME/src/pico-sdk ..
+[...]
+
+$ make -j
+[...]
+
+$ ls
+CMakeCache.txt  cmake_install.cmake  generated  main.dis  main.elf.map  main.uf2  pico-sdk
+CMakeFiles      elf2uf2              main.bin   main.elf  main.hex      Makefile  pioasm
+
+$ cp main.uf2 /media/$USER/RPI-RP2
+
+$ screen /dev/ttyACM0
+The I2C baudrate is 399361 Hz
+Sensor serial number is: 0x8a7e 0xbb07 0x3ba0
+CO2: 1111 ppm, Temperature: 28.4 C (83.1 F), Humidity: 60.4%
+CO2: 1080 ppm, Temperature: 28.5 C (83.2 F), Humidity: 61.1%
+CO2: 1070 ppm, Temperature: 28.4 C (83.1 F), Humidity: 61.7%
+[...]
+```

sample-implementations/RaspberryPi_Pico/hardware.jpg

@@ -1,18 +1,24 @@
-#include "hardware/i2c.h"
-#include "pico/binary_info.h"
-#include "pico/stdlib.h"
 #include "../../scd4x_i2c.h"
+
+#include <hardware/i2c.h>
+#include <pico/stdlib.h>
+#include <pico/time.h>
+
 #include <stdio.h>
 
 int main(void) {
     stdio_init_all();
 
-    // Setup I2C using GPIO pins 16 & 17.
+    // Give us a few seconds to start viewing the output if we're plugged into
+    // the computer over USB.
+    sleep_ms(3000);
+
+    // Setup I2C using GPIO pins 12 & 13.
     const uint desired_clock_hz = 400 * 1000;
     const uint actual_baudrate = i2c_init(i2c_default, desired_clock_hz);
     printf("The I2C baudrate is %u Hz\n", actual_baudrate);
-    const uint sda_pin = 16;
-    const uint scl_pin = 17;
+    const uint sda_pin = 12;
+    const uint scl_pin = 13;
     gpio_set_function(sda_pin, GPIO_FUNC_I2C);
     gpio_set_function(scl_pin, GPIO_FUNC_I2C);
     gpio_pull_up(sda_pin);
@@ -73,7 +79,7 @@ int main(void) {
         const float temperatureFahrenheit = temperatureCelsius * 1.8f + 32;
         const float humidityPercent = humidityRaw / 1000.0f;
 
-        printf("CO2: %d ppm, Temperature: %.1f°C (%.1f°F), Humidity: %.1f%%\n",
+        printf("CO2: %d ppm, Temperature: %.1f C (%.1f F), Humidity: %.1f%%\n",
             co2Ppm, temperatureCelsius, temperatureFahrenheit, humidityPercent);
     }
 }