Music Synthesis Using the 555 Timer

Chris Whiting & Keddy Malcolm

Overview

555 Timer Pin Layout 555 Timer Configuration 555 Timer – Other Applications Malcolm Results Whiting Results Conclusion Sources

555 Timer Pin Layout

2 TRIG OUT rises, and interval starts, when this input falls below 1/3 VCC.

6 THR The interval ends when the voltage at THR is greater than at 2/3 Vcc.

4 RESETA 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.

5 CTRL "Control" access to the internal voltage divider (by default, 2/3 VCC).

7 DISOpen collector output; may discharge a capacitor between intervals. In phase with output.

3 OUT This output is driven to approximately 1.7V below +Vcc or GND.

555 Timer Pin Descriptions

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

555 Timer Pin Descriptions

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

555 Timer - Other Applications

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

555 Timer - Other Applications

Linear Ramp

555 Timer - Other Applications

Pulse Width Modulator

555 Timer - Other Applications

Frequency Divider

Malcolm-Design Overview Week 1

Switch Placement

Design Overview Week 2

Assembly Problems

Week One:• Change resistors to get frequencies correct• Mistakes in wiring

Week Two:• Problems with wiring• Balance between volume and waveform output• Component Precision

Malcolm Results Week 1

Theory Actual High Time Low Time Duty Cycle RB RA261.625 260.7 1.86ms 1.76ms 51.38% 26.7k .995k293.664 290.7 1.64ms 1.66ms 49.70% 23.9k329.627 335 1.42ms 1.42ms 50.00% 20.49k349.228 351.2 1.41ms 1.41ms 50.00% 19.6k391.995 390.6 1.27ms 1.28ms 49.80% 17.6k

440 431 1.14ms 1.12ms 50.44% 15.9k493.883 494 1.02ms 1.01ms 50.25% 13.8k523.251 530.8 968us 948us 50.52% 12.86k

Waveform Results: 259 Hz

• Rise time: 1.86 ms• Fall time: 1.76 ms• Duty Cycle: 51.38%

Waveform Results: 293 Hz

• High Time: 1.64ms• Low Time : 1.66ms• Duty Cycle: 49.7%

Waveform Results: 329 Hz

• High Time: 1.42ms • Low Time: 1.42ms• Duty Cycle: 50%

Waveform Results: 349 Hz

• High Time: 1.41ms• Low Time: 1.41ms• Duty Cycle: 50%

Waveform Results: 391 Hz

• High Time: 1.27ms• Low Time: 1.28ms• Duty Cycle: 49.80%

Waveform Results: 440 Hz

• High Time 1.14ms• Low Time 1.12ms• Duty Cycle: 50.80%

Waveform Results: 493 Hz

• High Time: 1.02ms • Low Time: 1.01ms• Duty Cycle: 50.44%

Waveform Results: 523 Hz

• High Time: 968us • Low time: 948 us• Duty Cycle: 50.25%

Malcolm Results Week Two

Theory Calculated frequency current261.625 264Hz 270.54Hz 16.7mA293.664 295Hz 303.55 Hz 17.3mA329.627 343Hz 354.93 Hz 17.4mA349.228 358Hz 372.66 Hz 17.5mA391.995 397Hz 416.67 Hz 17.6mA

440 439Hz 462.01 Hz 17.9mA493.883 503Hz 528.73 Hz 18mA523.251 539Hz 580.81 Hz 18.2mA

Waveform Results: 261 Hz

Waveform Results: 293 Hz

Waveform Results: 329 Hz

Waveform Results: 349 Hz

Waveform Results: 391 Hz

Waveform Results: 440 Hz

Waveform Results: 493 Hz

Waveform Results: 523 Hz

Overall Results

Frequencies and duty cycle very accurate in first stage

Frequencies loose accuracy in the second stage

Excellent sine wave poor volume quality

Chris’ Final Circuit Diagram

Used potentiometers in the lab to more accurately obtain desired output frequencies

Chris’ 555 Timer Circuit

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.

Chris’ Filter Circuit

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)

Chris’ Filter Circuit

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.

Chris’ Results – Square Wave

Theoretical & Experimental results for 555 timer circuit square wave output

Chris’ Results – Square Wave

Different resistances attributed to: Potentiometers, inaccurate capacitors, 555 timer

18.52% Difference?!

Chris's Results – Sine Wave

Theoretical & Experimental results for 555 timer and filter combination sine wave output

Chris's Results – Sine Wave

Different resistances attributed to: Potentiometers, inaccurate capacitors, 555 timer

20.08% Difference?!

Chris's Results – Sine Wave

Square wave to Sine Wave conversion Duty Cycle = 50.0% 0.2% error on average

Chris's Results – Sine Wave

Square wave to Sine Wave conversion Duty Cycle = 50.0% 0.2% error on average

524.091Hz 523.063Hz

Conclusion

555 Timer Pin Layout 555 Timer Configuration 555 Timer – Other Applications Malcolm Results Whiting Results

Sources

http://blog.makezine.com/2008/01/29/how-to-guitar-hero-autowh/

http://www.ecelab.com/circuit-astable-555.htm

http://www.cc.gatech.edu/classes/AY2011/cs3651_spring/docs/LM555.pdf

http://home.cogeco.ca/~rpaisley4/LM555.html

Questions?