This schema produces a random "Yes" or "No" with a single button press - indicated by the illumination of a red or green LED. The schema has two advantages over similar diagram. First, it uses just a single momentary contact pushbutton, so no on-off switch is required. When the pushbutton is pressed, an oscillator comprising the 10nF capacitor and 22kΩ resistor at pins 1 & 2 is almost immediately stopped by FET Q1, which pulls the oscillators timing capacitor to the positive rail. However, the 220nF capacitor and 470kΩ resistor in the gate schema of Q1 introduce a tenth of a seconds delay, so that about 250 oscillations take place before the clock is stopped.
Due to variations in charge on the diagram capacitors, as well as voltage and temperature variations, and the unpredictability of when the pushbutton will be pressed, randomness is assured. The schema has a high degree of randomness because it takes advantage of a near-perfect complementary square waveform at pins 10 and 11 of the 4047 IC. The oscillator frequency (available at pin 13) is passed through an internal divide-by-2 schema in the 4047. This appears at pin 10 (Q), and is inverted at pin 11 (Q-bar), thus assuring a near perfect 50:50 duty cycle for the two LEDs.
Yes-No Indicator Circuit Diagram
Note:
However, that the "impartiality" of the schema is partly contingent on the value of the 10nF capacitor and on a reasonably equal current flow through both LEDs. Over five trials, the Yes-No Indicator scored 142 Yes, 158 No, with Yes falling behind No in the fourth trial. Because the schema only works while switch S1 is pressed, standby current is zero, therefore a miniature 12V battery may be used to power it. In this case the schema could be used thousands of times before the battery would run flat. The schema has a further potential use. If the LEDs are omitted and a piezo (capacitive) sounder is wired directly to pins 10 and 11, it will produce a loud beep when equipment is turned on, and will continue to draw less than 0.5mA until it is switched off. The frequency of the beep may be changed by altering the value of the 10nF capacitor and its duration by altering the value of the 220nF capacitor.
However, that the "impartiality" of the schema is partly contingent on the value of the 10nF capacitor and on a reasonably equal current flow through both LEDs. Over five trials, the Yes-No Indicator scored 142 Yes, 158 No, with Yes falling behind No in the fourth trial. Because the schema only works while switch S1 is pressed, standby current is zero, therefore a miniature 12V battery may be used to power it. In this case the schema could be used thousands of times before the battery would run flat. The schema has a further potential use. If the LEDs are omitted and a piezo (capacitive) sounder is wired directly to pins 10 and 11, it will produce a loud beep when equipment is turned on, and will continue to draw less than 0.5mA until it is switched off. The frequency of the beep may be changed by altering the value of the 10nF capacitor and its duration by altering the value of the 220nF capacitor.
Author: Thomas Scarborough - Copyright: Silicon Chip Electronics
