Down with dogs and canes? A guide to the new electronic mobility

In this guide, I'm going to first introduce you to some simple aids that warn you of obstacles, and then we'll move on to some that provide quite sophisticated spatial information - obstacle detectors, sweeping sonar systems and optical devices.

Imagine you are standing in a large room. You clap your hands, sending out a pulse of sound. You hear the sound echoing back off the walls. The larger the room, the further away you are from the walls, the longer it takes for you to hear the echo. The same thing happens if you flash a light. It sends out a pulse of light, which is reflected and you can see this reflection. But with light it happens so quickly that you won't notice any delay.

Simple obstacle detecting mobility aids work just like this. They send out a pulse of sonar (ultrasound) or laser light and receive back the echoes or reflection. They calculate the distance to the object using the time lapse between transmitting the signal and receiving the echo or reflection. Both sonar and laser are able to detect much smaller objects than can be detected with audible sound and the human ear. (For the techies, this is because they have a much shorter wavelength so reflect off even small objects, rather than bending around them as audible sound does).

Perhaps the most widely publicised is the Ultracane, which combines a sonar obstacle detector with a long cane. One sonar sensor detects obstacles straight ahead, whilst a second detects obstacles at head height. Each sensor operates a separate button on the cane handle, which vibrate when an obstacle is detected. There are two modes - one to detect obstacles within a 3m range, the other reduces this range to 1.5m. The Ultracane is available from Sound Foresight and costs £399 £15 delivery.

Using similar technology but offering much greater flexibility is the Miniguide - a truly mini sonar obstacle detector. The audio Miniguide beeps to warn you of obstacles - the higher the pitch of the beep the closer the obstacle is. The tactile Miniguide vibrates to warn you of obstacles - the faster the vibrations the closer the obstacle. The Miniguide is usually handheld but can be attached to things - for example cane, wheelchair or even a hat. It has a maximum range of 4m, and multiple modes make it well suited to many different situations. It is available from GDP Research in Australia and costs $550 Australian dollars (approximately £230).

The Laser Cane combines a laser obstacle detector with the long cane. It can detect obstacles ahead, at head height and to the sides, as well as detecting drop-offs. It vibrates and has an optional audible beep to warn you of obstacles. It is available from Nurion Industries in the US and costs $2500 US dollars (approximately £1340).

Some surfaces echo sonar or reflect laser light better than others. The hard surface of a wall will be detected by sonar at a greater distance than soft furniture. Laser will pass straight through glass meaning that it can't be detected.

Sonar devices occasionally suffer from interference from other sources of ultrasound. For example, the air breaks on buses emit ultrasound. If this is picked up by the sonar sensor you'll be told there's an obstacle there when really there isn't.

Simple sonar devices cannot satisfactorily detect drop-off such as steps going down or the edges of platforms, but laser can.

Simple obstacle detectors based on pulse technologies only tell you that there is an object within range and how far away the nearest object is.

Some systems use advanced sweeping sonar and others use visible light to provide information about objects, such as their shape, and about spatial relationships between multiple objects.

These mimic the way in which bats navigate. They emit a prolonged sonar signal. The frequency (pitch) of this signal changes over time. This enables the device to obtain a continuous sound image of the environment. This is converted into a sound picture in the audible sound range so that you can hear it. Every object creates a unique pattern of echoes, so you will hear a unique pattern of beeps, known as a sound signature. By remembering this sound signature you can recognise the object. You can also hear where objects are in relation to each other.

An example of this kind of system is the BAT 'K' Sonar Cane, which combines a long cane with a small sweeping sonar device attached to the handle. The audio output is through specially-designed earphones that enable you to hear noises around you, as well as listening to the sound pictures through the cane. It is available from Bay Advanced Technologies in New Zealand and costs $600 US dollars (approximately £325).

Sweeping sonar devices are occasionally subject to interference and detect some surfaces better than others.

Optics (visible light) can be used to provide sound pictures similar to those created by sweeping sonar devices, but without the disadvantages of interference. These systems use a camera to gather visual information and convert this into a sound picture.

An example is the vOICe - Seeing With Sound software for either PC, notebook or even some mobile phones. The vOICe software is free, but you will need a computer with webcam or a camera enabled mobile phone to use it. It creates a sound picture providing information about multiple objects and every object creates a unique sound signature.

Technology may not yet have made your guide dog or long cane redundant, but it does provide you with more choice, greater flexibility and can overcome some of the problems of both canes and dogs.