Add README.md for Arduino fan controller project with features, usage, and schematic

README.md

@@ -0,0 +1,81 @@
+# Arduino Fan Controller
+
+This project is an Arduino-based fan controller that allows you to adjust the speed of a 4-pin PWM fan using a push button. It also measures and displays the fan's RPM via the serial monitor.
+
+## Features
+- PWM control of a 4-pin fan
+- RPM measurement using the fan's tachometer output
+- Speed adjustment in 10% increments via a push button
+- Serial output of current speed and RPM
+
+## Hardware Requirements
+- Arduino board (Uno, Nano, etc.)
+- 4-pin PWM fan
+- NPN transistor (for PWM control)
+- Push button
+- Resistors (as needed for button and transistor)
+- Wires and breadboard
+
+## Pin Configuration
+- **pwmPin (9):** PWM output to transistor base
+- **tachPin (2):** Tachometer input from fan
+- **buttonPin (7):** Push button input
+
+## How It Works
+- The fan speed is controlled by PWM signal on pin 9.
+- The push button on pin 7 increases the speed by 10% each press, cycling from 0% to 100%.
+- The tachometer signal from the fan is read on pin 2 using an interrupt to count pulses.
+- Every second, the RPM is calculated and printed to the serial monitor along with the current speed percentage.
+
+## Usage
+1. Connect the hardware as described above.
+2. Upload the `ArduinoFanController.ino` sketch to your Arduino.
+3. Open the serial monitor at 9600 baud to view speed and RPM.
+4. Press the button to increase fan speed in steps.
+
+## Schematic
+
+Below is a simple schematic for connecting the components (updated for a 5V fan, 1kΩ resistor, and two capacitors in parallel to the fan):
+
+
+```
+				 +5V (Fan Power)
+						 |
+					 [Fan]
+						 |
+				 +---+---+
+				 |   |   |
+				 |   |   +-- PWM (Pin 9, Arduino) via 1kΩ resistor
+				 |   +------ Tach (Pin 2, Arduino)
+				 |
+				GND
+				 |
+			[C1] 100uF Electrolytic
+			[C2] 104pF Ceramic
+			(C1 and C2 in parallel to the fan)
+
+	 [Button]
+		 |
+	 Pin 7 (Arduino)
+		 |
+		GND
+
+	 [NPN Transistor]
+	 Collector: Fan GND
+	 Base: PWM (Pin 9, Arduino) via 1kΩ resistor
+	 Emitter: Arduino GND
+```
+
+**Notes:**
+- The fan is powered by 5V.
+- A 1kΩ resistor is used between Arduino pin 9 (PWM) and the transistor base.
+- Two capacitors (100uF electrolytic and 104pF ceramic) are connected in parallel to the fan for noise filtering and stability.
+- The tachometer wire goes directly to Arduino pin 2.
+- The button is connected between pin 7 and ground, with a pull-up resistor enabled in code.
+
+## Notes
+- The RPM calculation assumes the fan generates 2 pulses per revolution.
+- You can modify the code to set the speed via serial input (see commented section in the code).
+
+## License
+This project is open source and free to use for personal and educational purposes.