P1f(i) Data Transmission You will learn about: How Infrared is used Analogue and Digital Signals

Infrared uses The Daily Mail published this image of criminals using an infrared camera. The camera was able to detect and record their actions when it was dark using the heat they emitted. Remote controls emit infrared signals when a button is pressed. They have lots if uses from switching a television channel, opening a garage door or using a wireless mouse. We learned previously that an analogue wave can have many values. Digital signals only have two. These are on and off. The image shows that on is represented by a 1 and off is represented by a 0. A remote control sends a signal made up of on and off pulses. The receiver decodes it to change a channel or whatever else it is programmed to do. An advantage of digital coding is that any noise can easily be noticed and removed. Analogue waves vary in amplitude and frequency. Frequency denotes pitch. Amplitude denotes loudness. An analogue wave is continuously variable.

Digital Control When you press a button on your remote control a digital signal is transmitted. The circuit sends this signal to a light emitting diode, LED, to the front of the remote control. The signal includes a: Start command Instruction command (channel 1 or volume up) Device code, or address (model of television) Stop command If you have a camera on your mobile phone video the end of your remote control and press a button. Your camera may be able to detect the infrared signal that our eyes cannot.

Questions 1.When an infrared burglar alarm detects movement what it is detecting? 2.A wristwatch has hands on it that point to the numbers between 1 – 12. Describe whether this is analogue or digital? 3.Look at the image at the right. Describe how on and off are represented. How is this different to the image shown below it?

Questions 1.When an infrared burglar alarm detects movement what it is detecting? The heat source – the person. 2.A wristwatch has hands on it that point to the numbers between 1 – 12. Describe whether this is analogue or digital? Analogue as it has a range of values from 1 to 12 and a continuous range of values between. 3.Look at the image at the right. Describe how on and off are represented. How is this different to the image shown below it? Above image shows length of pulse for on and off – short pulses for off, or 0, and longer pulses for on, 1. The bottom image shows height or wave for on and off – high is on, or 1, and low is off, or 0.