4

Figure 2 shows the typical waveforms generated during this

mode of operation, and Figure 3 gives the family of time

Repeat Cycle Timer (Astable Operation)

Figure 4 shows the CA555 connected as a repeat cycle

timer. In this mode of operation, the total period is a function

the duty cycle is:

Typical waveforms generated during this mode of operation

are shown in Figure 5. Figure 6 gives the family of curves of

free running frequency with variations in the value of

3V

3.3V

5V

0

0

0

INPUT

VOLTAGE (TERMINAL 2)

CAPACITOR

VOLTAGE (TERMINALS 6, 7)

OUTPUT

VOLTAGE

(TERMINAL 3)

FIGURE 2. TYPICAL WAVEFORMS FOR RESET TIMER

TIME DELAY(s)

10

1

0.1

0.01

0.001

10k

Ω

1

10

100

V+ = 5V

100k

Ω

1M

Ω

10M

Ω

FIGURE 3. TIME DELAY vs RESISTANCE AND CAPACITANCE

1

CA555

EO

8

5

2

6

7

3

4

0.01

µF

RELAY

COIL

V+

5V

FIGURE 4. REPEAT CYCLE TIMER (ASTABLE OPERATION)

t

1

t

1

t

2

+

----------------

=

R

1

R

2

+

R

1

2R

2

+

------------------------

CA555, CA555C, LM555C