LED Circuit Introduction
This project uses 7 LED (Light Emittng Diode) to simulate the rolling of a dice after the Roll button is pushed. It has a slowdown feature so that you can see the 'rolling' of the dice slowing down and then stop. This is more satisfying than the usual LED dice circuit which just stops after the button is released.
LED Circuit Description
Pressing 'Roll' switch
When the switch is turned on Q4 is turned off (its base is pulled high by the 3.3M ohm resistor) and the 555 oscillator is not oscillating. Pressing the ROLL switch immediately charges the 470nF capacitor, Q4 is turned ON and the 555 starts to oscillate. The 470nF gradually discharges via the 10M ohm and 3.3M ohm resistors and turns Q4 off.
555 IC oscillator
The 555 is connected as an oscillator. The frequency of oscillation is generally independent of the potential difference across the pins. However, as Q4 turns off the frequency becomes dependent on the voltage.
The 14017 decade counter
The counter CPo is advanced by a LOW to HIGH transition from pin 3 of the 555 to pin 14. The first six outputs from the 14017 labelled are labelled by Oo to O5. The next output O6 from pin 5 is conected to the Reset pin 15. The table below lists the output sequence, which pin it appears at, what dice number is shown and which LED's are illuminated.
The last column allows us to interpret the resistor and LED connections. Note that LED's 2 and 6 are always on except when a value of 1 comes up. So a HIGH on pin 1 turns off LED's 2 and 6 and turns on LED 4 which shows the value 1. When none of the pins have a HIGH (that is when pin 10 is HIGH but is not connected anywhere) then only LED's 2 & 6 (dice value 2) are on.
Parts List
The parts list of the LED circuit is shown below.
