Chris Whiting & Keddy Malcolm
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555 Timer Pin Layout
555 Timer Configuration
555 Timer – Other Applications
Malcolm Results
Whiting Results
Conclusion
Sources
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
RESET
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.
5
CTRL
"Control" access to the internal voltage divider
(by default, 2/3 VCC).
7
DIS
Open 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.
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•
•
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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
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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
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Two modes of operation:
 Monostable Mode – Output Single Pulse
 Astable Mode – Output Continuous Pulses
 Bistable Mode – Output acts as Basic Flip-Flop
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Linear Ramp
Pulse Width Modulator
Frequency Divider
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Linear Ramp
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Pulse Width Modulator
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Frequency Divider
Switch Placement
Week One:
• Change resistors to get frequencies correct
• Mistakes in wiring
Week Two:
• Problems with wiring
• Balance between volume and waveform output
• Component Precision
Theory
261.625
293.664
329.627
349.228
391.995
440
493.883
523.251
Actual High Time Low Time Duty Cycle
RB
260.7
1.86ms 1.76ms 51.38%
26.7k
290.7
1.64ms 1.66ms 49.70%
23.9k
335
1.42ms 1.42ms 50.00%
20.49k
351.2
1.41ms 1.41ms 50.00%
19.6k
390.6
1.27ms 1.28ms 49.80%
17.6k
431
1.14ms 1.12ms 50.44%
15.9k
494
1.02ms 1.01ms 50.25%
13.8k
530.8
968us
948us
50.52%
12.86k
RA
.995k
• Rise time: 1.86 ms
• Fall time: 1.76 ms
• Duty Cycle: 51.38%
• High Time: 1.64ms
• Low Time : 1.66ms
• Duty Cycle: 49.7%
• High Time: 1.42ms
• Low Time: 1.42ms
• Duty Cycle: 50%
• High Time: 1.41ms
• Low Time: 1.41ms
• Duty Cycle: 50%
• High Time: 1.27ms
• Low Time: 1.28ms
• Duty Cycle: 49.80%
• High Time 1.14ms
• Low Time 1.12ms
• Duty Cycle: 50.80%
• High Time: 1.02ms
• Low Time: 1.01ms
• Duty Cycle: 50.44%
• High Time: 968us
• Low time: 948 us
• Duty Cycle: 50.25%
Theory Calculated frequency
261.625 264Hz 270.54Hz
293.664 295Hz 303.55 Hz
329.627 343Hz 354.93 Hz
349.228 358Hz 372.66 Hz
391.995 397Hz 416.67 Hz
440
439Hz 462.01 Hz
493.883 503Hz 528.73 Hz
523.251 539Hz 580.81 Hz
current
16.7mA
17.3mA
17.4mA
17.5mA
17.6mA
17.9mA
18mA
18.2mA
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Frequencies and duty cycle very accurate in
first stage
Frequencies loose accuracy in the second
stage
Excellent sine wave poor volume quality
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Used potentiometers in the lab to more accurately obtain
desired output frequencies
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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.
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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)
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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.
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Theoretical & Experimental results for 555 timer
circuit square wave output
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Different resistances attributed to:
 Potentiometers, inaccurate capacitors, 555 timer
18.52% Difference?!
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Theoretical & Experimental results for 555 timer and
filter combination sine wave output
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Different resistances attributed to:
 Potentiometers, inaccurate capacitors, 555 timer
20.08% Difference?!
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Square wave to Sine Wave conversion
Duty Cycle = 50.0%
0.2% error on average
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Square wave to Sine Wave conversion
Duty Cycle = 50.0%
0.2% error on average
524.091Hz
523.063Hz
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555 Timer Pin Layout
555 Timer Configuration
555 Timer – Other Applications
Malcolm Results
Whiting Results
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http://blog.makezine.com/2008/01/29/howto-guitar-hero-autowh/
http://www.ecelab.com/circuit-astable555.htm
http://www.cc.gatech.edu/classes/AY2011/cs
3651_spring/docs/LM555.pdf
http://home.cogeco.ca/~rpaisley4/LM555.ht
ml