REALTIME CONTROL

UPN Laser Transceiver

! NB ! Crystal have stopped producing the DIL version of the CS8130. The SSOP version doesn't fit the PCB, and is so small it's very difficult to solder by hand. The specified laser diode is also out of production.

We no longer supply kits for this transceiver. We the hope the following information is of interest to some despite this.
 
 

Introduction

The UPN Laser Transceiver (UPNLT) connects computers using laser beams.

A pair of  UPNLTs can provide a full-duplex 115.2 kbit/sec data connection between the serial ports of two computers which are separated by a distance of many hundreds of metres. Once initialised, the UPNLTs are transparent to the computers and the computers see the connection as a hard-wired connection supporting TXD and RXD signals.

The UPNLT was designed as a physical layer link for the UPN, but it also has more general application where a data link between two computers is required and practical or cost considerations disallow the use of hard wired connection.

The major advantages UPNLTs have over other wireless technologies are

The major disadvantages of a UPNLT link are The need for stable mounting is by far the most significant disadvantage. Building structures often move with time, temperature and wind. Building foundations also generally move. Anticipate at least monthly realignment for all but short (<100 metre) links between very stable buildings.
 



 


The UPNLT design is copyright. However, permission is granted to individuals, educational institutions and non-profit organisations to copy the design for their own use.

A review of the UPNLT appears in the Feb 1998 issue of "Electronics Australia" magazine.

Specification

Maximum range without additional lenses: 500 metres in clear weather (note 1)
Recommended maximum range without additional lenses: 450 metres (allowing for loss through two clean, clear glass windows) (note 1)
Data rate: 1200 to 115200 bits/second (configurable)
Mode: Full duplex, ie. data can flow in both directions simultaneously
Signals supported: TXD and RXD.
Computer interface: Pseudo-RS232. The UPNLT serial port signals do not swing negative, as is specified for RS232. This is generally of no consequence, as almost all computer serial ports treat a 0 volt signal as a negative signal.
Maximum cable length from UPNLT to computer: 20 metres (typ.)
Laser beam modulation/encoding: IrDA SIR
Laser wavelength: 670 nm, visible red
Laser power: < 5mW peak pulse power (2.8 mW typ.), < 1mW average power (.56 mW typ.) (note 1)
Laser Class: Class 2, classification per AS/NZS 2211.1.1997  (note 1, note 2, note 3)
Typical beam cross section: 5 mm x 2.5 mm at collimating lens, 4.5 mm x 3 mm at waist, 150 mm x 75 mm at 500 metres.
Typical beam divergence: .3 mrad
PCB: 55 mm x 87 mm, single-sided
Case dimensions: 65 mm x 115 mm x 31 mm
Power requirements: 9 to 12 VDC @ 60 mA
Environmental: Ambient temperature range 0 to 40 degrees Celsius. Protection from rain and direct sunshine is necessary.
Vulnerability to environmental light: Performance is degraded if the sun's position is within approx 15 degrees of the receiver photodiode axis. Additional shielding can usually remedy this. Reflected sunlight does not normally degrade performance.
Initialisation requirements: Within 7 seconds of each UPNLT power-up, the attached computer must send the UPNLT a configuration string at 9600 baud. Approximately 7 seconds after power-up, a UPNLT switches automatically to data transfer mode.

Note 1:
The specifications and classification apply to UPNLTs manufactured by REALTIME CONTROL. It is likely that UPNLTs made from kits supplied by REALTIME CONTROL and adjusted in accordance with the instructions will be similar, but this can not be guaranteed.
It is the responsibility of the kit builder to determine the classification of any  laser device they build. The methods for determining classification depend on the particular country's law, but generally require at least measurement of power output and wavelength under various conditions.
It is the responsibility of the user of a laser device to ensure that the law is complied with in the country where it is used.

Note 2:
Extracts from AS/NZS 2211.1.1997
"9.2 Description of Laser Class
Class 2: Laser products which emit visible radiation in the wavelength range from 400 to 700 nm. Eye protection is normally afforded by aversion responses including the blink reflex."
"Class 3B: Laser products which emit either invisible or visible radiation and direct viewing is hazardous to the eye. Class 3B lasers are capable of causing eye injury either because their output is invisible and therefore aversion responses are not activated, or because the beam power is such that damage is done in shorter time than the blink reflex (.25 s). ..."
"11.4 Outdoor laser installations
11.4.1 Class 2 laser products Wherever reasonably practicable, the beam should be terminated at the end of its useful path, and the laser should not be aimed at personnel (at head height)."
"4.1.1 Modification  If the modification of a previously classified laser product affects any aspect of the product's performance or intended functions within the scope of this Standard, the person or organization performing any such modification is responsible for ensuring the reclassification and relabelling of the laser product."

Note 3:
A Class 2 laser can cause eye damage if a person deliberately forces himself to stare into the beam despite the strong natural reflex to avert his gaze.

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