When Arduino Meets Gemini: A Tiny AI That Talks Back

1#include <Arduino.h>
2#include <WiFiS3.h>
3#include <ArduinoHttpClient.h>
4#include <Arduino_LED_Matrix.h>
5#include "Font3x5.h"   // <-- compact 3x5 font
6
7// ==== Ultrasonic Pins ====
8#define TRIG_PIN 2
9#define ECHO_PIN 3
10
11// ==== Indicators ====
12#define RED_LED 4
13#define GREEN_LED 5
14#define BUZZER 6
15
16// ==== WiFi credentials ====
17const char ssid[] = "SSId";
18const char pass[] = "Password";
19
20// ==== Gemini API ====
21const char* host = "generativelanguage.googleapis.com";
22String gemini_api_key = "your API key";
23String model = "gemini-2.0-flash";
24
25// ==== LED Matrix ====
26ArduinoLEDMatrix matrix;
27uint8_t frame[8][12] = {0};   // 8 rows × 12 cols display buffer
28
29// ---- Distance Measurement ----
30long getDistance() {
31  digitalWrite(TRIG_PIN, LOW); delayMicroseconds(2);
32  digitalWrite(TRIG_PIN, HIGH); delayMicroseconds(10);
33  digitalWrite(TRIG_PIN, LOW);
34  return pulseIn(ECHO_PIN, HIGH) * 0.034 / 2;
35}
36
37// ---- Show Scrolling Text ----
38void pushColumn(uint8_t colData) {
39  for (int row = 0; row < 5; row++) {       // only 5 rows for 3x5 font
40    for (int c = 0; c < 11; c++) frame[row][c] = frame[row][c+1];
41    frame[row][11] = (colData >> row) & 0x01;
42  }
43  matrix.renderBitmap(frame, 8, 12);
44}
45
46void scrollText(const char* text, int speed) {
47  for (int i = 0; text[i] != '\0'; i++) {
48    char c = text[i]; 
49    if (c < 32 || c > 127) c = '?';
50    for (int col = 0; col < 3; col++) {   // 3 columns per character
51      uint8_t colData = pgm_read_byte(&Font3x5[c - 32][col]);
52      pushColumn(colData);
53      delay(speed);
54    }
55    pushColumn(0x00); delay(speed);  // space between letters
56  }
57  for (int i = 0; i < 6; i++) { pushColumn(0x00); delay(speed); }
58}
59
60// ---- Gemini Request ----
61String askGemini(String prompt) {
62  WiFiSSLClient client;
63  HttpClient geminiClient(client, host, 443);
64
65  String body = "{\"contents\":[{\"parts\":[{\"text\":\"" + prompt + "\"}]}]}";
66
67  geminiClient.beginRequest();
68  geminiClient.post("/v1beta/models/" + model + ":generateContent?key=" + gemini_api_key,
69                    "application/json", body);
70  geminiClient.endRequest();
71
72  int statusCode = geminiClient.responseStatusCode();
73  String response = geminiClient.responseBody();
74
75  if (statusCode != 200) {
76    Serial.print("Gemini API error: ");
77    Serial.println(statusCode);
78    return "Error!";
79  }
80
81  // Extract first reply text
82  int idx = response.indexOf("\"text\":"); 
83  if (idx == -1) return "No reply";
84  int start = response.indexOf("\"", idx + 7) + 1;
85  int end = response.indexOf("\"", start);
86  String answer = response.substring(start, end);
87
88  // cleanup
89  answer.replace("\\n", " ");
90  answer.replace("\\", "");
91
92  return answer;
93}
94
95// ---- Setup ----
96void setup() {
97  Serial.begin(115200);
98  matrix.begin();
99  pinMode(TRIG_PIN, OUTPUT);
100  pinMode(ECHO_PIN, INPUT);
101  pinMode(RED_LED, OUTPUT);
102  pinMode(GREEN_LED, OUTPUT);
103  pinMode(BUZZER, OUTPUT);
104
105  Serial.println("Connecting to WiFi...");
106  WiFi.begin(ssid, pass);
107  while (WiFi.status() != WL_CONNECTED) { delay(500); Serial.print("."); }
108  Serial.println("\n✅ WiFi connected!");
109  Serial.println("System ready. Wave your hand in front of sensor to start.");
110}
111
112// ---- Loop ----
113void loop() {
114  long distance = getDistance();
115  if (distance > 0 && distance < 50) {
116    scrollText("WELCOME TO GEMINI", 120);
117    delay(1000);
118
119    if (Serial.available()) {
120      String question = Serial.readStringUntil('\n');
121      question.trim();
122      if (question.length() == 0) return;
123
124      // Show question on Serial
125      Serial.println("Q: " + question);
126
127      // Gemini thinking
128      digitalWrite(RED_LED, HIGH); 
129      String answer = askGemini(question);
130      digitalWrite(RED_LED, LOW);
131
132      // Show answer on Serial
133      Serial.println("Gemini: " + answer);
134
135      // Indicate + scroll answer
136      digitalWrite(GREEN_LED, HIGH);
137      tone(BUZZER, 1000, 200);  // short beep
138      scrollText(answer.c_str(), 150);
139      digitalWrite(GREEN_LED, LOW);
140    }
141  }
142}