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Presented by Tim Surtell in association with
Kelsey Park School Electronics Club Computer & Software Services Limited
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Lecture Outline 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
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The ‘Black Box’ of Electronics
Power Process Input(s) Output(s)
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The Block Diagram Input Process 1 Process 2 Process 3 Output
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The 555 Timer – A Black Box! 555 1 8 2 7 3 6 4 5 Eight connections called ‘pins’ Little white dot and dimple denote pin 1
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The 555 Timer – A Black Box! 0V 1 8 Vs 2 7 555 3 6 4 5
The 555 uses a 3 – 18V DC power supply
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The 555 Timer – A Black Box! 0V 1 8 Vs Trigger 2 7 555 3 6 Reset 4 5
The Trigger and Reset inputs
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Switches Connecting a switch to the Trigger input: 1st attempt!
0V Switch Trigger input
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Switches Connecting a switch to the Trigger input: 2nd attempt! Vs
Bang!
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Switches Connecting a switch to the Trigger input of the 555 using a pull-up resistor Vs 1kΩ resistor 0V Switch Trigger input
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The 555 Timer 0V 1 8 Vs Trigger 2 7 555 Output 3 6 Reset 4 5
The 555 Output
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Lamps Connecting a lamp to the 555 Output by ‘sourcing’ current Output
0V Lamp Output
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Lamps Connecting a lamp to the 555 Output by ‘sinking’ current Vs
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Light Emitting Diodes (LEDs)
0V LED Output Resistor R
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Relays 0V Diode Output Relay Coil Vs Motor Relay Switch M
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The 555 Timer 0V 1 8 Vs Trigger 2 7 Discharge 555 Output 3 6 Threshold
Reset 4 5 Offset Connections for the timing components
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555 Timer Circuits Three basic circuits… The bistable The monostable
The astable
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Bistable Block Diagram
Trigger Input 555 Output Reset Input The bistable Output is stable in both states, high and low
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Bistable Timing Diagram
Trigger Input Output Reset Input Bistable Triggered Bistable Reset
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Monostable Block Diagram
Trigger Input 555 Output Timing Components The monostable Output is stable in the low state only Triggering makes the Output go high for a set length of time
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Monostable Timing Diagram
Trigger Input Output Monostable Triggered Time period T
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The Timing Components Vs 0V Resistor R Capacitor C
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Astable Block Diagram Output
555 Output Timing Components The astable Output is not stable at all. It repeatedly goes high for a set time and then low for a set time
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Astable Timing Diagram
Output Tmark Tspace
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The Timing Components Vs 0V Resistor R1 Capacitor C Resistor R2
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The Timing Components
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Practical Matters Three ways to build circuits…
Breadboard for prototypes Stripboard to produce final design Printed Circuit Board (PCB) to produce final design
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Breadboard
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Stripboard
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Printed Circuit Board (PCB)
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Lecture Summary 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
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Resistors Resistance is measured in Ohms (Ω)
Most resistors have four coloured bands Band 2 2nd Digit Band 3 Multiplier Band 4 Tolerance Band 1 1st Digit
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The Resistor Colour Code
Band 1 1st Digit Band 2 2nd Digit Band 3 Multiplier Band 4 Tolerance Black x 1 - Brown 1 x 10 1% Red 2 x 100 2% Orange 3 x 1,000 Yellow 4 x 10,000 Green 5 x 100,000 Blue 6 x 1,000,000 Violet 7 Grey 8 White 9 Gold 5% Silver 10%
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Construction – The Resistors
The 1kΩ resistors Brown Black Red Gold 5% 1 00
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Construction – The Resistors
Resistors R1 and R2: 1kΩ (brown, black, red, gold)
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Construction – The Resistors
Grey Red Brown Gold 5% 8 2
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Construction – The Resistors
Resistor R3: 820Ω (grey, red, brown, gold)
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Diodes Diodes only let current flow through them in one direction
1N4001 Rectifier Diode + - 1N4148 Signal Diode + -
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Construction – The Diodes
Diode D1: 1N4001 (black with grey band)
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Construction – The Diodes
Diodes D2 and D3: 1N4148 (orange with black band)
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Light Emitting Diodes (LEDs)
Like diodes, current only flows through them in one direction Three ways of identifying negative lead: The shortest lead - + Largest ‘triangle’ inside the LED Flat on the LED package
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Construction – The LED LED D4: Green 3mm LED
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Construction – The 555 Timer
IC1: 555 IC Holder
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Construction – The Jumper Pins
J1 and J2: ‘Smoothing’ and ‘Relay’ jumpers
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Capacitors Metallised Polyester Capacitors
Electrolytic Capacitors (polarised) - +
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Construction – Capacitors
Capacitors C1 and C2: 0.01μF (blue)
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Construction – Capacitors
Capacitor C3: 220μF (smallest black)
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Construction – Capacitors
Capacitor C4: 1000μF (largest black)
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Construction – Variable Resistor
Variable Resistor VR1: 100kΩ
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Construction – Terminal Blocks
Terminal Blocks TB1 and TB2
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Construction – The Relay
Relay RL1
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Time to Power Up! 0V +12V Button M Motor
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