Never look directly into a laser beam.
Either the Windows UPNLT software or other software can be used for
testing.
1. Using the Windows UPNLT software.
Focus adjustment
The focus of the laser is adjusted by rotating the end of the laser diode
housing containing the lens.
Select Tools, Laser control, and turn on the laser. Adjust the laser focus
to give minimum spot size on an object at least 10 metres away.
To adjust the focus for longer range links, set it to give minimum spot size
on an object more than 50 metres away. This must generally be done at night,
as the spot will not be visible in daylight.at this range.
Laser power adjustment
If a laser power meter is available then -
Select Tools, Laser control, and turn on the laser. Adjust VR1 for .56 mW
optical power output.
Optical loopback test
Place a reflective object (almost anything "shiny" suffices, a softdrink can is ideal) about 200 mm in front of the laser, so that a little of the light from the laser is reflected back into the photodiode.
Run the UPNLT program.
Select Tools, Link test. Move the reflective object until the message "Receiving
file" is displayed.
If the reflector directs too much of the laser beam back to the photodiode,
the receiver will overload and no data will be received. If the reflector
returns too little of the beam, then either no data or incorrect data will
be received.
Optimising receiver sensitivity
Remove any nearby reflective object from the laser beam.
Run the UPNLT program.
Select Settings, Receiver sensitivity. Set the sensitivity to 1.
Select Tools, Link test. Expect the program to indicate that the transceiver is receiving bytes despite there being no optical signal into the photodiode. This "data" is noise.
Repeat the process to determine the lowest numbered sensitivity setting which gives no data received when there is no optical signal.
2. Using other software.
A terminal program is required for this test. Telix or a similar package which supports 115200 baud is preferable, but software such as Windows Terminal is sufficient for testing at lower data rates. Higher speeds cause a higher laser duty cycle, making the beam reflection easier to see.
Power up and initialise the UPNLT to a baud rate supported by the terminal software.
Wait until LED2 on the UPNLT switches off, then start the terminal software. Configure it to 8 data bits, 1 stop bit, no parity, and to suit the UPNLT baud rate. Disable both hardware (CTS/RTS) handshaking and software handshaking (XON/XOFF).
Place a reflective object (almost anything "shiny" suffices, a softdrink can is ideal) about 200 mm in front of the laser, so that a little of the light from the laser will be reflected back into the photodiode.
Hold down an alpha or numeric key on the computer, thus sending a continuous (but widely spaced) series of characters. Move and rotate the reflective object until these characters are displayed correctly on the computer screen as the transceiver converts the characters to light, then converts the reflected light back into electrical signals which it returns to the computer.
If the reflector directs too much of the laser beam back to the photodiode, the receiver will overload and no data will be displayed. If the reflector returns too little of the beam, then either no data or incorrect data will be displayed.
Remove the reflective object from the laser path.
Use the terminal program's Upload ASCII file facility to send a continuous stream of data to the UPNLT. ("Upload" any convenient file.) The laser will be much brighter when the UPNLT is fed with this continuous stream of data. Adjust the laser focus to give minimum spot size on an object at least 10 metres away.
To optimise the focus for long range links, set it to give minimum spot size on an object at least 50 metres away. This must generally be done at night, as the spot will not be visible during daylight.at this range.
To maximise the brightness of the laser during focusing, send a file comprising all 0 bytes, ensure that the terminal program is not configured to insert pauses between characters or lines, and send at the highest possible baud rate.
A file comprising all 0 bytes can be created using the following QBASIC program:
OPEN "ALLZEROS" FOR OUTPUT AS #1
FOR J=1 TO 1000000: PRINT #1, CHR$(0);: NEXT
END
Use similar methods to perform the remaining adjustments described in "Using the Windows UPNLT software". Send a contiguous uninterrupted stream of zero bytes at 115200 bps for adjustment using a laser power meter.