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-# tachometer
+# Arduino nano tachometer
 
+# Program Functionalities
+
+This Arduino program is designed to interface with a two-channel incremental encoder and display the rotational speed of a roller on an LCD screen. The main functionalities of the program include:
+
+## Initialization of LCD and Encoder Pins
+- The program initializes a 16x2 I2C LCD to display the calculated speed.
+- It sets up two digital pins as inputs with internal pull-up resistors to read signals from the encoder.
+
+## Interrupt Handling for Encoder Pulses
+- The program uses external interrupts on the encoder signal pins (CLK and DT) to accurately count pulses.
+- Two interrupt service routines (ISRs) are defined: `ai0()` and `ai1()`. These routines increment the pulse counter based on the state of the encoder signals, ensuring the counter increases only in one direction to prevent negative values.
+
+## Real-Time Calculation of RPM and Speed
+- The main loop of the program calculates the RPM (revolutions per minute) and the speed in meters per minute (m/min) every second.
+- RPM is calculated using the formula:  
+  \[
+  \text{RPM} = \frac{\text{counter} \times 60}{\text{pulses per revolution}}
+  \]
+- The speed in m/min is calculated using the formula:  
+  \[
+  \text{Speed (m/min)} = \frac{\text{RPM} \times \pi \times \text{roller diameter}}{1000}
+  \]
+- After each calculation, the counter is reset for the next measurement period.
+
+## Displaying Speed on the LCD
+- The calculated speed in m/min is displayed on the LCD screen.
+- The LCD is updated every second with the new speed value, ensuring the display shows real-time data.