BE Lesson 8: Using the 555 IC timer chip .

• What is a 555 integrated circuit (IC) timer?• Make a blinking LED circuit using a 555 timer.• Make a railroad signal light using a second LED.• Vary the oscillation period.• Make an English police siren. • Make an electronic canary.

© 2012 C. Rightmyer, Licensed under The MIT OSI License, 20 July 2012

The 555 timer IC (integrated circuit)

physical appearance

schematic symbol

555

tim

er IC

12

345

67

8 GND

Trigger

Output

ResetControl voltage

Threshold

Discharge

Vcc

BE ckt 8-1. Using IC 555 to blink an LED

+

vo

lts

220

LED6.8K

16K

+10 F

on on on

off off offoff

Pin 3 voltage observedusing an oscilloscope

R1

R2R3

C1

555

12

345

67

8

[http://www.kpsec.freeuk.com/555timer.htm]

Hookup diagram for ckt 8-1

1 2 3 4

5678

16K

+10 F

6.8K

555

+

9.0

volts

LED1220

+

BE ckt 8-2. Adding a second LED to ckt 8-1

+

vo

lts

220

LED16.8K

16K

+10 F

R1

R2R3

C1

555

12

345

67

8

LED2

220

R4

Hookup diagram for ckt 8-2

1 2 3 4

5678

LED1

16K

+10 F

6.8K

555

+

9.0

volts

220

220

LED2

+

+

BE ckt 8-3. Change the flashing cycle for ckt 8-2

+

vo

lts

6.8K

1K

+10 F

R1

R2

C1

R3

100K pot

555

12

345

67

8

220

LED1

R3

LED2

220

R4

Hookup diagram for ckt 8-3

1 2 3 4

5678

LED1

+10 FC1

6.8K

555+

9.0

volts

220

220

LED2

R4

1K

100 k pot

BE ckt 8-4. An English police siren

+

vo

lts

220

1K

120K

+0.01 F

R1

R2

R3

C1

470K R4

3904B

C

E

R5 10

NO

555

12

345

67

8

Hook up diagram for ckt 8-4

1 2 3 4

5678120K

+0.01 F

1K

555

+

9.0

volts3904

10

220

470K

bce

BE ckt 8-5. A chirping canary?

6.8K

33K

+

0.01 F

R5

R6

C2

.1 FR7

1K

R3

33K

NO

555

12

345

67

8

C3

3904B

C

E

3906B

C

E

+

F

R4

C1

47

R2

R13.3K

100K pot

+

volts

Hook up diagram for ckt 8-5

.01 F+

3904

10 F

3.3K

100Kpot

NO

+

9.0

volts

+

3906

bce

1K

b ce

33K1 2 3 4

567833K

6.8K

47

.1 F