1. AQA GCSE 7 Electronic systems processing Design and Technology 8552
Unit 2
Energy, materials, systems and devices 7

2. Objectives
Understand the difference between analogue and digital signals
Understand how microcontrollers are programmed as counters, timers and for decision making to provide functionality to products and processes
Understand the use of buzzers, speakers and lamps to provide functionality to products and processes

3. Do products make decisions?
How does an electronic dice know which number to display?
What is a process?
Timing
Counting
Amplifying
Comparing
Name any other electronic processes you have come across

4. Digital vs analogue
There are two types of signal in electronic systems:
Analogue signals have an infinite range of values between the minimum and maximum points
Digital signals are either on or off, and are usually represented by a 0 for off and a 1 for on
Which type of signal is a switch likely to produce?

5. Integrated Circuit (IC)
Also known as microchips, ICs are capable of performing specific tasks
There are many different types of IC
A programmable IC is called a microcontroller
ICs come in all different shapes and sizes
Most come in a dual in line (DIL) package

6. Microcontroller IC
A microcontroller IC is known as a peripheral interface controller (PIC)
These programmable ICs are very adaptable
They can be programmed to perform multiple processes
This reduces the amount of components needed to perform a task (component redundancy)
What are the benefits of having a smaller circuit board?

7. Programming a PIC
A PIC’s functions are controlled by a program or code that is received via a download cable
Specialist software enables the program to be drawn graphically as a flowchart
It can also be written in a coding language, such as BASIC
Most PICs can be reprogrammed multiple times, allowing for corrections and updates
What might be the drawback of using a PIC for a simple one-off task?

8. Digital or analogue inputs?
When programming PICs, the type of input required will need to be considered, for example:
Switches are input components that give a digital signal
Components such as thermistors, LDRs and microphones require an analogue input

9. Using analogue sensors
PICs cannot process the infinite range of values that analogue inputs provide so it is divided into smaller parts
Analogue inputs divide a signal in to 256 equal sections
The range is labelled 0 to 255
When the input signal reaches a particular value or intensity, the PIC will function as the program dictates

10. Input components
Complete Task 1 of Worksheet 7

11. Output components Buzzers and speakers produce sound
Buzzers normally give out a set frequency meaning they are good for system alerts
Speakers have a broader frequency range and are used for speech and audio
Suggest one instance where a buzzer would be more appropriate than a speaker

12. Two timers Timing is a critical process in a circuit
Many microcontrollers have an accurate internal clock
Time delays can be programmed
Monostable devices are single-shot timers, going on once, then staying off
Astable devices constantly alternate between on and off
Which device does a flashing road beacon use?

13. Monostable device
The single pulse produced is usually triggered by a switch or sensor
The length of the pulse can be varied by changing the delay time
Monostable devices are used for timing how long events occur such as an automatic door opening and shutting
Where else might one be used?

14. Astable device
The stream of pulses produced are oscillating and constant
One cycle is the time (t) a single pulse takes to go from 0 (off) to 1 (on) and back to 0
The speed of the pulses is known as the frequency and is measured in hertz (Hz)
Flashing lights are used on tall buildings and aircraft – where else are they used?

15. Counting
PICs can be programmed to count up and down, and can take over the roles of many traditional ICs
Popular counters include the decade counter (4017) which has 10 outputs and counts up or down one on each pulse
7-segment display decoder (4026) converts pulses into numbers and outputs to a 7-segment display
Both of these ICs can ‘cascade’ – what does this mean?

16. Worksheet 7
Complete Task 2 of the worksheet

17. Plenary
When you download a track from a music site, how does the file get onto your computer or device?
What happens to the track when you play it through speakers or headphones?