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REQUIRED MATERIALS: Multisim Circuit Simulation Software 555 Timer Data Sheet 555 TIMER, ASTABLE MULTIVIBRATOR - Theory The 555 timer isn't really a digital device at all. It's found in the Mixed IC parts bin along with the Mono- stable for that reason, Figure 1 shows the Multisim 555 model in its astable Multi-vibrator configuration. The 555 timer is an excellent choice for a rectangular wave timing/trigger source. The external components $R_1$, $R_2$, and $C$ determine the frequency of oscillation ($f$) and the duty cycle ($D$). Capacitor $C$ is only for decoupling the control input (CON) from noise and has no effect on the frequency. Equations used to determine the necessary values are: $f = \frac{1}{T}$ Duty Cycle $= \frac{t_1}{T}$ $t_1 = R_2 C [ln(2)]$ $t_2 = (R_1 + R_2)C [ln(2)]$ $T = t_1 + t_2 = \text{period}$ $R_1 (min) = 1k\Omega = \text{IMPORTANT!!}$ Figure 1 The discussion which follows is an example of how the device works. If you would like to go into more detail about how its internal comparator's work, go to Stanley's Operational Amplifiers EET 330 textbook If you haven't had EET 210/220 yet, feel free to investigate how the transistor in the circuit works in Stanley's Devices text book (or just about any other book that discusses transistors) EET 315 || Fall 2018 || Lab 2 || REV 5 8/29/2018 2 OF 7 Before designing a 555 Astable Multivibrator, let's look at how it works inside. Observe Figure 2 below. It demonstrates the charge and discharge paths.

          REQUIRED MATERIALS:
Multisim Circuit Simulation Software
555 Timer Data Sheet
555 TIMER, ASTABLE MULTIVIBRATOR - Theory
The 555 timer isn't really a digital device at all. It's found in the Mixed IC parts bin along with the Mono-
stable for that reason, Figure 1 shows the Multisim 555 model in its astable Multi-vibrator configuration.
The 555 timer is an excellent choice for a rectangular wave timing/trigger source. The external components
$R_1$, $R_2$, and $C$ determine the frequency of oscillation ($f$) and the duty cycle ($D$). Capacitor $C$ is only for
decoupling the control input (CON) from noise and has no effect on the frequency.
Equations used to determine the necessary values are:
$f = \frac{1}{T}$
Duty Cycle $= \frac{t_1}{T}$
$t_1 = R_2 C [ln(2)]$
$t_2 = (R_1 + R_2)C [ln(2)]$
$T = t_1 + t_2 = \text{period}$
$R_1 (min) = 1k\Omega = \text{IMPORTANT!!}$
Figure 1
The discussion which follows is an example of how the device works. If you would like to go into more
detail about how its internal comparator's work, go to Stanley's Operational Amplifiers EET 330 textbook
If you haven't had EET 210/220 yet, feel free to investigate how the transistor in the circuit works in
Stanley's Devices text book (or just about any other book that discusses transistors)
EET 315 || Fall 2018 || Lab 2 || REV 5
8/29/2018
2 OF 7
Before designing a 555 Astable
Multivibrator, let's look at how it works
inside. Observe Figure 2 below. It
demonstrates the charge and discharge
paths.

REQUIRED MATERIALS:
Multisim Circuit Simulation Software
555 Timer Data Sheet
555 TIMER, ASTABLE MULTIVIBRATOR - Theory
The 555 timer isn't really a digital device at all. It's found in the Mixed IC parts bin along with the Mono-
stable for that reason, Figure 1 shows the Multisim 555 model in its astable Multi-vibrator configuration.
The 555 timer is an excellent choice for a rectangular wave timing/trigger source. The external components
R1, R2, and C determine the frequency of oscillation (f) and the duty cycle (D). Capacitor C is only for
decoupling the control input (CON) from noise and has no effect on the frequency.
Equations used to determine the necessary values are:
f = (1)/(T)
Duty Cycle = (t1)/(T)
t1 = R2 C [ln(2)]
t2 = (R1 + R2)C [ln(2)]
T = t1 + t2 = period
R1 (min) = 1kΩ = IMPORTANT!!
Figure 1
The discussion which follows is an example of how the device works. If you would like to go into more
detail about how its internal comparator's work, go to Stanley's Operational Amplifiers EET 330 textbook
If you haven't had EET 210/220 yet, feel free to investigate how the transistor in the circuit works in
Stanley's Devices text book (or just about any other book that discusses transistors)
EET 315 || Fall 2018 || Lab 2 || REV 5
8/29/2018
2 OF 7
Before designing a 555 Astable
Multivibrator, let's look at how it works
inside. Observe Figure 2 below. It
demonstrates the charge and discharge
paths.

Added by Bianca H.

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