Page 230 - ARM Based Microcontroller Projects Using MBED

216 8. INTERMEDIATE LEVEL PROJECTS

//
// Read the output voltage of the LDR, then calculate the resistance
// of it and finally calculate and display the light level in lux
//
while(1) // Do forever
{
mV = 3300.0f * LDR.read(); // In mV
R = 10.0 * mV / (3300.0 - mV); // LDR resistance
lux = 2.17 - 1.28 * log10(R); //
lux = pow(10.0, lux); // Light level (Lux)
gotoscr('4', '0'); // Line 4, col 0
MyPC.printf("Light Level (lux) = %5.2f", lux);

wait(1.0); // Wait 1 second
}
}

FIG. 8.83, CONT’D

FIG. 8.84 Typical display of the light level.

8.25.2 Aim

The aim of this project is to show how the flashing rate of the User LED can be changed by
using a potentiometer.

8.25.3 Block Diagram

The block diagram of the project is shown in Fig. 8.85.

FIG. 8.85 Block diagram of the project.