Web Posted on: September 3, 1998
Practical environmental controls using new advanced low cost technology
Graham Manson
Currabinny Electronics
Eastern Villas
Currabinny,Carrigaline
Co. Cork, Ireland.
Tel: +353 21 378642
fax: +353 21 922498
email: mansong@indigo.ie
1. Summary
New infra red, radio and acoustic links were studied. The practicality of using this advanced, low cost technology in aids for daily living were studied. Research is continuing in this area to enable user selection of the properties of the interface module with quality aiming at M3S standards.
2. Introduction
The availability and wide use of devices to improve quality of life depends on suitable technology and cost: portable telephones have become more common as technology has provided smaller apparatus at a much lower cost than before.
Complex factors, including fashion, affect the success of devices: in all cases commercial success and general availability depends on users’ choice.
2.1 Users’ needs
No group should have their control system facilities dictated by suppliers. For adaptability devices should be available in modular form and properties should be adjustable by the user. As a starting point, controllers for devices, such as street crossings, home entertainment centres, doors and room lights were designed and assumptions were made regarding control range ( in room only, very close proximity or longer distance) and on type of feedback to confirm successful control action. However, as control range, and feedback could be freely selected, the end user defined the properties of the controller and thus had independence.
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3 New system design
All systems were reviewed, including those commercially developed and not specifically for wheelchair use. Thus mass produced systems which may provide very high specification at low cost could be considered.
3.1 Bus systems
It may be useful to use local suppliers for computer parts to ensure good availability and low cost. Therefore, all interfaces, including those supplied with standard computers were considered.
3.1.1 Parallel bus
Parallel data transfer is potentially faster than serial transfer but requires more wires.
3.1.1.1. GPIB
The General Purpose Interface Bus (IEEE-488-1975/ANSI MC1.1 and with different connector IEC 625) can transfer 8 bit words at 1 M byte per second. Up to 15 devices may be connected to the bus with a total cable length of 20 m and maximum cable length between devices of 2 m. The interface and cable is expensive, and the interface has to be specially purchased (it is not fitted as standard to computers).
3.1.1.2 SCSI
The Small Computer System Interface is fitted to all Apple Macintosh computers and a card may be purchased for fitting to PCs. The basic specification interface transfers data 8 bits wide at 5 M transfers per second over a distance of 6 m. The SCSI-3 will allow transfer of 16 bit words at 10 M transfers per second over a distance of 25 m.
3.1.1.3 Parallel Printer- Centronics
The parallel printer port is fitted to all IBM type PCs. It is designed for printers and provides 8 bit wide signal transfer in one direction only (from computer to an external device) and such transfer can only be made every 15 m s because of the time requirement for busy and acknowledgement signals. However, the two status ports, select and error, may operate in 1 m s enabling this universal parallel port to be used as a fast serial interface transferring 1 M bits per second over a distance up to 2m.
3.1.2 Serial bus
Serial ports are potentially slower than parallel ports but they require less wires in the links and are improving with new technology.
3.1.2.1 Serial Port IBM
At least one serial port is available on every IBM PC. It uses the RS232 interface and may transfer 9 600 baud over 310 m (1 000 ft.). The standard version has a maximum transfer rate of 19 200 baud but newer versions allow transfer at 112 000 baud up to 2 m.
3.1.2.2 Serial Port Apple
The serial port on the Apple uses the RS422 interface so may transfer data at 10 M bits per second over 12 m, and 112 000 baud over 4 000 ft or 1 200 m.
3.1.2.3 M3S
The M3S bus is a multiple master, multiple slave bus, an intelligent integrated and modular system for the rehabilitation environment (ISO/TC173/SCI/WG7). It is a thoroughly defined system with all functions considered (for example eye gaze, open door, tongue switches). The bus has two power lines, two safety lines and two pairs of lines for Controlled Area Network (CAN). Transfer rate is 250 k bit per second . This bus would be the one of choice for wheel chair and environment control but the cost of long distance communication may be reduced by some use of the two wire Future bus.
3.1.2.4 Field bus
The field bus is an open system (standard EN 50170). Data transfer is over two wires using RS485, with data rates of 12 M bits per second up to 100 m and 187 500 at distances of 1 km. Up to 32 devices may be attached to the common bus without repeaters and 127 devices with repeaters.
3.2 Devices
For reliability, all devices need coding to eliminate errors from interference. Coding and error elimination chips such as the Plessey SL486 may be used. ( This was designed for radio controlled models and is low cost.) Newer complex codes may be programmed in microcontrollers.
3.2.1 Infra Red
An infra red control for use within a room was successfully produced some years ago using a wide angle high power short pulse light emitter and decoding with a Plessey SL486 ( a low cost circuit designed for model control).
Infra red is useful within rooms. Experiments confirmed that Infra Red transmission at 950 nm through glass is attenuated by a very small amount, so Infra Red may be contained within a room by doors and walls but can go through windows.
Problems can be encountered in bright daylight but the new infrared IrDA compliant transceivers ( Hewlett Packard HSDL-1000) are low cost, have a very sharp attenuation beyond ± 30° , and work at 115.2 k baud from 1 cm to 1 m even in sunlight of 10 klux. This should prove useful for control and communication at short range even out of doors.
3.2.2 Ultrasound
Experiments were performed with 40 kHz ultrasound. Attenuation through 2.4 mm glass was greater than 60 dB so containment of the signal within a room is certain. The signal field with the transducers used was 3 dB down at ± 30° so wide reception within a room is possible, and intimate communication possible out of doors with little interference. Operation with short pulses at resonance would allow a communication signal rate of 10 kHz.
3.2.3 Radio
Low power radio at 418 MHz is allowed in the U.K. with a signal bandwidth of 2 kHz and an expected range up to 100 m. This range may be useful although the range achieved depends on surrounding environment, such as steel in buildings.
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4 Overview
The devices are all small enough to allow all three to be available on one module. Selection of radio, infra red or sound will give, respectively, long range control, in sight control and control immune from light interference.
The user will be given a choice of all three transmission modes and the desired combination of feedback ( for example, sound, light or tactile) to confirm that action has been taken. Full properties, including repeat tries, if any, per action request will also be user specified.
The system will thus give the user complete choice of control properties. Analysis of such choice will indicate technical failings of interfaces so, for example, interference from bright sunlight or radio signals may be judged and equipment improved.
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5 Conclusion
Three remote link technologies (infra red, sound and radio) and one fast bus developed for wide commercial use have been considered. All are open systems.
Work is continuing in the area but the aim is to produce systems of low cost with properties dictated by the user. Generally devices should conform to standards, such as the M3S bus, but for long range information transfer a faster bus may be considered and for local devices micro controllers as well as computers may be used (equipment as modules) to produce high quality at low cost.
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