The circuit is rather simple. Main parts are the microcontroller, the light sensor and the RGB-LED. The sensor and R4 are forming a voltage divider. An ADC (Analog Digital Conversion) channel at pin 3 is used to read the values of the sensor. The circuit is designed for 5V power supply. It has no integrated power regulator.source

The stepper motor will turn the ultrasonic range finder in 360 degrees and reverse (Cool, isn’t it?). When two measurements have been made, the PIC will send out the data to the PC by using an asynchronous interrupt transfer. The timer in the PIC controls the stepping motor turning speed.source

The circuit to light LED with single 1.5V battery is usually based on a blocking oscillator or a charge-pumped voltage doubler.This is another (but similar to charge pump) way to flash LED with 1.5V battery. The base-R voltage becomes nearly double the Vcc while making oscillation timing of astable multivibrator. LED can be flashed if it is attached aside. Since the LED discharges the C electricity, oscillator timing is shortened.source

With this circuit it is possible to operate a LED from a single 1.5 Volt cell. The LED will flash about every second. The circuit including two resistors,two capacitor , one LED and one 74HCT04.source

The idea of this project came from Olivier’s youngest son. He was dreaming of a small tool able to write symbols or pictures on a screen. As a graphic LCD (even bought at Crownhill ) was too expensive (or too easy??), the solution adopted was to pilot a matrix of Leds. This way, with only some cheap transistors, common red Leds, and a PIC16F628 , the dream could become reality.source