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Computer & Software Services Limited. Kelsey Park School Electronics Club. Presented by Tim Surtell in association with. In this lecture we’ll look at… The ‘black box’ concept Using the 555 timer IC Three 555 timer circuits Practical matters After the break…

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Computer & Software Services Limited

Kelsey Park School Electronics Club

Presented byTim Surtellin association with


In this lecture we’ll look at…

The ‘black box’ concept

Using the 555 timer IC

Three 555 timer circuits

Practical matters

After the break…

Hands-On session:Build your 555 monostable circuit

Lecture Outline


The ‘Black Box’ of Electronics

Power

Input(s)

Output(s)

Process


The Block Diagram

Process 1

Process 2

Process 3

Input

Output


Eight connections called ‘pins’

The 555 Timer – A Black Box!

555

1

8

2

7

3

6

4

5

  • Little white dot and dimple denote pin 1


The 555 uses a 3 – 18V DC power supply

The 555 Timer – A Black Box!

0V 1

8 Vs

2

7

6

3

5

4

555


The Trigger and Reset inputs

The 555 Timer – A Black Box!

0V 1

8 Vs

Trigger 2

7

6

3

5

Reset 4

555


Switches

Trigger input

Switch

0V

  • Connecting a switch to the Trigger input: 1st attempt!


Switches

Vs

Trigger input

Switch

0V

  • Connecting a switch to the Trigger input: 2nd attempt!

Bang!


Switches

Vs

Trigger input

1kΩ resistor

Switch

0V

  • Connecting a switch to the Trigger input of the 555 using a pull-up resistor


The 555 Output

The 555 Timer

0V 1

8 Vs

Trigger 2

7

6

Output 3

5

Reset 4

555


Lamps

Output

Lamp

0V

  • Connecting a lamp to the 555 Output by ‘sourcing’ current


Lamps

Vs

Output

Lamp

  • Connecting a lamp to the 555 Output by ‘sinking’ current


Light Emitting Diodes (LEDs)

Output

Resistor R

LED

0V


Relays

Output

Vs

Motor

M

RelaySwitch

RelayCoil

Diode

0V

0V


Connections for the timing components

The 555 Timer

0V 1

8 Vs

Trigger 2

7 Discharge

6 Threshold

Output 3

5 Offset

Reset 4

555


Three basic circuits…

The bistable

The monostable

The astable

555 Timer Circuits


The bistable Output is stable in both states, high and low

Bistable Block Diagram

Trigger Input

555

Output

Reset Input


Bistable Timing Diagram

Trigger Input

Reset Input

Output

Bistable Triggered

Bistable Reset


The monostable Output is stable in the low state only

Triggering makes the Output go high for a set length of time

Monostable Block Diagram

Timing Components

555

Trigger Input

Output


Monostable Timing Diagram

Trigger Input

Output

Time period T

Monostable Triggered


The Timing Components

Vs

Resistor R

Capacitor C

0V


The astable Output is not stable at all.It repeatedly goes high for a set time and then low for a set time

Astable Block Diagram

Timing Components

555

Output


Astable Timing Diagram

Output

Tmark

Tspace

Tmark

Tspace


The Timing Components

Vs

Resistor R1

Resistor R2

Capacitor C

0V


The Timing Components


Three ways to build circuits…

Breadboard for prototypes

Stripboard to produce final design

Printed Circuit Board (PCB) to produce final design

Practical Matters


Breadboard


Stripboard


Printed Circuit Board (PCB)


What you have learned…

How to treat a system as a ‘black box’ with inputs, a process, and outputs

How to break a problem into small blocks

How to use the 555 timer IC inputs and outputs

What the bistable, monostable and astable circuits do

How to test and construct circuits

Lecture Summary


Resistors

Band 1

1st Digit

Band 2

2nd Digit

Band 3

Multiplier

Band 4

Tolerance

  • Resistance is measured in Ohms (Ω)

  • Most resistors have four coloured bands


The Resistor Colour Code

Colour

Band 11st Digit

Band 22nd Digit

Band 3Multiplier

Band 4Tolerance

Black

0

0

x 1

-

Brown

1

1

x 10

1%

Red

2

2

x 100

2%

Orange

3

3

x 1,000

-

Yellow

4

4

x 10,000

-

Green

5

5

x 100,000

-

Blue

6

6

x 1,000,000

-

Violet

7

7

-

-

Grey

8

8

-

-

White

9

9

-

-

Gold

-

-

-

5%

Silver

-

-

-

10%


Construction – The Resistors

Brown

Black

Red

Gold

1

0

00

5%

The 1kΩ resistors


Construction – The Resistors

Resistors R1 and R2: 1kΩ (brown, black, red, gold)


Construction – The Resistors

Grey

Red

Brown

Gold

8

2

0

5%

The 820Ω resistor


Construction – The Resistors

Resistor R3: 820Ω (grey, red, brown, gold)


Diodes

1N4001 Rectifier Diode

-

+

1N4148 Signal Diode

-

+

  • Diodes only let current flow through them in one direction


Construction – The Diodes

Diode D1: 1N4001 (black with grey band)


Construction – The Diodes

Diodes D2 and D3: 1N4148 (orange with black band)


Light Emitting Diodes (LEDs)

  • Three ways of identifying negative lead:

  • The shortest lead

  • Flat on the LED package

-

+

  • Like diodes, current only flows through them in one direction

  • Largest ‘triangle’ inside the LED


Construction – The LED

LED D4: Green 3mm LED


Construction – The 555 Timer

IC1: 555 IC Holder


Construction – The Jumper Pins

J1 and J2: ‘Smoothing’ and ‘Relay’ jumpers


Capacitors

Metallised Polyester Capacitors

Electrolytic Capacitors (polarised)

-

+


Construction – Capacitors

Capacitors C1 and C2: 0.01μF (blue)


Construction – Capacitors

Capacitor C3: 220μF (smallest black)


Construction – Capacitors

Capacitor C4: 1000μF (largest black)


Construction – Variable Resistor

Variable Resistor VR1: 100kΩ


Construction – Terminal Blocks

Terminal Blocks TB1 and TB2


Construction – The Relay

Relay RL1


Time to Power Up!

M

0V

+12V

Button

Motor


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