U1

LM555CN

GND

1

DIS7OUT 3RST4

VCC

8

THR6

CON5TRI2

PrimaryPower12 V

C1uF

OnOff

Key = S

LoadPower12 V

RV1

Key = A 100kOhm

50%

12VRelay

EDR201A12

K

Buzzer

200 Hz

555 Time Delay

0

( ) [ (0) ]t t

C Cf C Cfv t v v v e

RC

General Expression for Charging a Capacitor

12

(0) 0

1

Cf

C

v V

v V

RC RV C

1( ) 12 [0 12]t

RV CCv t e

Substituting

1( ) 12 [0 12]t

RV CCv t e

1

1

1

1

11

1

1

1

1

1

1

( ) 12 12

8 12 12

4 12

1

31

ln3 1

1ln 13

1.09 1 1.1 1

t

RV CC

t

RV C

t

RV C

t

RV C

v t e

e

e

e

t

RV C

t RV C

t RV C RV C