feat: Initialize backend with NestJS framework and serial communication

- Added package.json for backend dependencies and scripts.
- Implemented basic AppController and AppService with a simple "Hello World!" endpoint.
- Created SerialModule for handling serial communication with the Pico.
- Developed SerialController and SerialService to manage serial ports and commands.
- Implemented event streaming for serial data.
- Added Jest tests for AppController and e2e tests for the application.
- Set up TypeScript configuration for the backend.
- Created frontend SendBox component for sending commands to the backend.
- Established Pico firmware for controlling a stepper motor via serial commands.
- Documented project structure and usage in README files.

pico/src/Stepper.h

@@ -0,0 +1,15 @@
+#pragma once
+// ...existing code...
+class Stepper {
+protected:
+    int steps_per_rev;
+public:
+    virtual void step(int steps, bool direction) = 0;
+    void step_rev(int revs, bool direction){
+        step(steps_per_rev*revs, direction);
+    }
+    int get_steps_per_rev(){
+        return steps_per_rev;
+    }
+    virtual ~Stepper() {}
+};

pico/src/ULN2003Stepper.h

@@ -0,0 +1,39 @@
+#pragma once
+#include <Arduino.h>
+#include "Stepper.h"
+#include <array>
+class ULN2003Stepper : public Stepper {
+private:
+    std::array<uint8_t, 4> pins;
+    static constexpr int steps_per_seq = 8;
+    const uint8_t sequence[8][4] = {
+        {1, 0, 0, 0},
+        {1, 1, 0, 0},
+        {0, 1, 0, 0},
+        {0, 1, 1, 0},
+        {0, 0, 1, 0},
+        {0, 0, 1, 1},
+        {0, 0, 0, 1},
+        {1, 0, 0, 1}
+    };
+    int step_delay_us = 5000;
+public:
+    ULN2003Stepper(std::array<uint8_t, 4> pins, int rev_steps) : pins(pins) {
+        steps_per_rev = rev_steps;
+        for (auto pin : pins) {
+            pinMode(pin, OUTPUT);
+        }
+    }
+    void step(int steps, bool direction) override {
+        for (int i = 0; i < steps; ++i) {
+            int seq_idx = direction ? (i % steps_per_seq) : (steps_per_seq - 1 - (i % steps_per_seq));
+            for (int j = 0; j < 4; ++j) {
+                digitalWrite(pins[j], sequence[seq_idx][j]);
+            }
+            delayMicroseconds(step_delay_us);
+        }
+    }
+    void setSpeed(int delay_us) {
+        step_delay_us = delay_us;
+    }
+};

pico/src/main.cpp

@@ -0,0 +1,53 @@
+#include <Arduino.h>
+#include "Stepper.h"
+#include "ULN2003Stepper.h"
+
+
+ULN2003Stepper driver1({18, 19, 20, 21}, 4096);
+int revSteps = 0;
+
+void setup() {
+  Serial.begin(115200);
+  revSteps = driver1.get_steps_per_rev();
+  Serial.print("Steps: ");
+  Serial.println(revSteps);
+}
+
+void loop() {
+  static String input = "";
+  while (Serial.available()) {
+    char c = Serial.read();
+    if (c == '\n' || c == '\r') {
+      if (input.length() > 0) {
+        Serial.print("Received: ");
+        Serial.println(input);
+        // Parse command
+        if (input.startsWith("STEP ")) {
+          int idx1 = input.indexOf(' ');
+          int idx2 = input.indexOf(' ', idx1 + 1);
+          int steps = input.substring(idx1 + 1, idx2).toInt();
+          int dir = input.substring(idx2 + 1).toInt();
+          driver1.step(steps, dir != 0);
+          Serial.print("Motor moved ");
+          Serial.print(steps);
+          Serial.print(" steps in direction ");
+          Serial.println(dir);
+        } else if (input.startsWith("SPEED ")) {
+          int delay_us = input.substring(6).toInt();
+          driver1.setSpeed(delay_us);
+          Serial.print("Speed set to ");
+          Serial.println(delay_us);
+        } else if (input.startsWith("LOG ")) {
+          Serial.print("LOG: ");
+          Serial.println(input.substring(4));
+        } else {
+          Serial.println("Unknown command");
+        }
+        input = "";
+      }
+    } else {
+      input += c;
+    }
+  }
+  delay(10); // avoid busy loop
+}