Starter – can you explain how this circuit works?

Buzzer

P6 – Electricity for Gadgets

Lesson 7 – Logic circuits

Learning aim: Demonstrate an understanding of logic gates and circuits in electrical systems

Learning Objectives Success Criteria

Recognise input and output signals for electronic systems with combinations of logic gates.

Complete truth tables for combinations of logic gates.

Describe how input signals for logic gates are obtained.

Recall and identify the input and output signals in an electronic system with a combination of logic gates. (Grade E-D)

Complete a truth table of a logic system with up to three /(or four) inputs made from logic gates. (Grade D-A)

Describe how to use switches, LDRs and thermistors in series with fixed resistors.(Grade C)

Explain how a thermistor or an LDR can be used with a fixed or variable resistor .(Grade C-A)

Practical applications LDR

0V

Vin

VOUT

Here’s a potential divider that is used to control light-activated switches…

When the light intensity on the LDR decreases its resistance will ________. This causes VOUT to _______ so the processor and output will probably turn _____. The variable resistor can be adjusted to change the ________ of the whole device.

Words – decrease, sensitivity, increase, off

HT

DEMO – circuit boards

Computer Logic Circuits

Made up of logic gates.Distinct units within the CPU

doing specific jobs.Simple in operation – clock speed

gives computers the power.

Electronic systemsElectronic systems are made up of 3 parts:

1) An INPUT SENSOR – these detect changes in the environment

Examples:

3) An OUTPUT DEVICE – these are controlled by the processor

Examples:

2) A PROCESSOR – these decide what action is needed

Examples:

Truth tables for three inputs

A burglar alarm

The alarm keeps sounding until the owner enters the code into the control panel, regardless of the input it receives.

Can you identify the input sensor, the processor and the output?

A burglar alarm is a great example of a control system.

input = movement sensor

processor = alarm unit

output = siren and lights

How does this happen?

input B

input A

This is an arrangement of two NOR gates. The output of one gate forms one input of the other.

The alarm contains a bistable latch, or ‘flip-flop’ circuit.

The bistable latch

Output

input Ainput Boutput

0

0

1

1

0

1

0

1

1

0

0

0NOR gate truth tablebistable latch

This arrangement is capable of storing a logic state; as such ‘flip-flops’ are used extensively in computer memory.

Three input truth tables question

Truth tables for four inputs

Build your own control system – p6 d01

To doComplete worksheet p6d01 to check understanding of logic gate systems

Extension workComplete questions 3 and 4 (p242-3)

AnswersQ1 logic gates; high; low; switch;

off; thermistor; light intensity;potential divider; adjusted

A B C D E

0 0 0 1 0

0 1 0 1 1

1 0 0 1 0

1 1 1 0 0

A B C D Output

0 0 0 1 0

0 1 1 0 0

1 0 1 1 1

1 1 1 0 0

2a

2b

A B C D E F

0 0 0 1 1 0

0 1 0 1 1 0

1 0 0 1 1 0

1 1 0 1 0 0

0 0 1 0 1 0

0 1 1 0 1 0

1 0 1 0 1 0

1 1 1 0 0 1

3

A B C D E F G H

0 0 0 0 1 1 0 1

0 0 0 1 1 0 1 1

0 0 1 0 1 0 1 1

0 1 0 0 0 1 0 0

1 0 0 0 0 1 0 0

1 1 0 0 0 1 0 0

0 0 1 1 1 0 1 1

0 1 0 1 0 0 1 1

0 1 1 0 0 0 1 1

1 0 1 0 0 0 1 1

0 1 1 1 0 0 1 1

1 1 1 0 0 0 1 1

1 0 1 1 0 0 1 1

1 1 0 1 0 0 1 1

1 1 1 1 0 0 1 1

4

Q3a the managerQ3b the vault opening

The bistable latch – how does it work?plenary

Stage 3 – Q: What will happen to the system if the movement sensor is triggered? Why?Stage 4 – Q: What will happen to the system when the sensor stops detecting movement? Why?Stage 5 – Q: What will happen to the system when the alarm code is entered? Why?Stage 6 – Q: What will happen to the system after the code is entered? Why?

Learning Objectives Success Criteria

Recognise input and output signals for electronic systems with combinations of logic gates.

Complete truth tables for combinations of logic gates.

Describe how input signals for logic gates are obtained.

Recall and identify the input and output signals in an electronic system with a combination of logic gates. (Grade E-D)

Complete a truth table of a logic system with up to three /(or four) inputs made from logic gates. (Grade D-A)

Describe how to use switches, LDRs and thermistors in series with fixed resistors.(Grade C)

Explain how a thermistor or an LDR can be used with a fixed or variable resistor .(Grade C-A)

To doRead through pages 244-5 and

make notes on the bi-stable latchComplete worksheet P6h4