2TRIG OUT rises, and interval starts, when this input falls below 1/3 V CC. 6THR The interval ends when the voltage at THR is greater than at 2/3 Vcc. 4RESET A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. 5CTRL "Control" access to the internal voltage divider (by default, 2/3 V CC ). 7DIS Open collector output; may discharge a capacitor between intervals. In phase with output. 3OUT This output is driven to approximately 1.7V below +Vcc or GND.
Square wave output, how? Capacitor Charge Time: T1 = 0.693(R1+R2)C1 Capacitor Discharge Time: T2 = 0.693(R2)C1 The output frequency is determined by the following equation: Simple astable configuration
Duty Cycle of waveform – Pulse Width/Period The Duty cycle is determined by the following equation: Duty Cycle Relationship to output frequency Large R2 wrt R1 Control capacitor reduces noise
Two modes of operation: Monostable Mode – Output Single Pulse Astable Mode – Output Continuous Pulses Bistable Mode – Output acts as Basic Flip-Flop Linear Ramp Pulse Width Modulator Frequency Divider
Frequencies and duty cycle very accurate in first stage Frequencies loose accuracy in the second stage Excellent sine wave poor volume quality
Used potentiometers in the lab to more accurately obtain desired output frequencies
R2 value determines output frequency. Duty Cycle unaffected because R2 >> R1 Various switches with potentiometers are used to act as selectors for the output frequency by turning each switch on or off.
555 Timer Square Wave Output Sine Wave A square wave is the sum of multiple sine waves at odd multiples of the square wave’s frequency (odd order harmonics)
Extract the fundamental frequency of the square wave by filtering the higher order sine waves. Low-pass filter with 600 Hz cutoff frequency and an inverting op-amp connected in series.