Faraday For Fun: An Electronic Batteryless Dice

Step 5 Dice Schematic

This step shows the circuit diagram for the dice. It consists of a rectifier diode bridge circuit to rectify the AC voltage produced by the Faraday generator and filtered with a 4700uF/25V electrolytic capacitor. The capacitor voltage is regulated with a LDO, LP-2950 with a 5V output voltage, which is used to provide supply voltage to the rest of the circuit, consisting of a microcontroller and LEDs.

I used 7 high efficiency 3-mm blue LEDs in transparent packaging, arranged in the dice form. The LEDs are controlled by an 8-pin AVR microcontroller, the ATTiny13. The voltage output from the faraday generator is a pulsed output. This pulsed output is conditioned with the help of a resistor (1.2KOhm) and a Zener diode (4.7V). The conditioned voltage pulses are sensed by the microcontroller to determine if the tube is being shaken. As long as the tube is shaken, the microcontroller waits. Once the user stops shaking the tube, the microcontroller generates a random number, using an internal 8-bit timer operating in free running mode and outputs the random number between 1 and 6, on the output LEDs. The microcontroller then again waits for the user to shake the tube again. Once the LEDs display a random number, the available charge on the capacitor is sufficient to light the LEDs for an average time of about 10 seconds. To get a new random number, the user must shake the tube a few times again.