52 Silicon chip Australia’s electronics magazine siliconchip.com.au
This hole is 25mm up from the out-
side base of the case opposite CON1. If
you only require a UHF transmission
range of less than 40m, the antenna
wires can be bent around the inside
perimeter of the box.
For maximum transmission range
(up to 200m), the stiff receiver anten-
na wire should pass through a small
hole in the upper edge of the box, and
the receiver wire similarly should pass
through a small hole in the lower edge
of the box.
Once it’s through, bend the tips over
to form small 3mm loops. That pre-
vents you poking your eye out on the
otherwise sharp end.
1mm wire is used so that the wire is
stiff enough to stay straight. The wire
exit holes should then be sealed with
a neutral cure silicone sealant.
The repeater PCB is held inside the
case by M3 screws that go into the in-
tegral threaded bushes in the base of
the box.
The Neoprene seal for the lid needs
to be placed inside the surround chan-
nel and then cut to size. The start and
finish gap in this seal should be along
the lower long edge of the lid.
Labelling it
To produce a front panel label, you
have several options.
For a rugged label, mirror the de-
sign and print it onto clear overhead
projector film (using film suitable for
your type of printer). This way, the ink
will be on the back of the film when
the label is affixed. Attach with clear
silicone sealant.
There are alternatives such as
“Dataflex”and “Datapol” labels for use
with inkjet and laser printers – you’ll
find more information and direct links
to these products at: http://www.siliconchip.
com.au/Help/FrontPanelsSolar panel or mains power
We used a 12V 5W Solar panel to
power the unit. A 6V panel would be
more efficient, since we are reducing
the voltage down to 5V. However, 6V
panels aren’t easy to find. The panel
power rating only needs to be 1W.
If you want to run the unit from
mains power, a 9V plugpack could be
connected to CON1 instead.
Make sure the plugpack is out of
the weather, with only the low volt-
age wires going to the repeater.
In this case, IC3 and the LiFePO 4 cell
are not required, although you could
leave them in so that the unit will run
even during power outages (assuming
the transmitting and receiving units
are also battery-powered).
If you’re leaving off IC3, you could
also omit F1, D2, LED3 as well as IC4
and its associated parts. The 5V output
from REG1 could then be directly used
to power the circuit by connecting a
wire link from the regulator output to
the 5V terminal at JP2.Setting up
It is essential that the shunt is not
placed on JP2 until VR3 is adjusted to
for 5V at the output of IC4. To do this,
insert the LiFePO 4 cell into the holder
and measure voltage between the GND
and TP5V PC stakes. Adjust VR2 for a
reading of 5V.Installation
The repeater should be mounted in
a location that will give good recep-
tion of the original UHF signal. TheLED indicators (LED1 and LED2) will
let you know if the signal is received
and retransmitted if a shunt is in-
stalled on JP1.
VR1 must be adjusted so that the
receive LED does not flash at all, or at
least not too often, when no signal is
being received. But if it’s adjusted too
far, the repeater will not work, so you
need to check that it is still retransmit-
ting valid data.
To achieve this, initially set VR1
fully clockwise and press S1 so that
the VR1 setting is updated. More of
the random signal noise will now be
detected and the receive LED will flash
now and then, followed by the trans-
mit LED. Adjust VR1 anticlockwise
a few degrees and press S1 to again
update the setting. Check that the re-
peater retransmits correctly.
If the repeater operates correctly, try
further anticlockwise adjustment. The
final adjustment will be a compromise
between reliable repeater operation and
noise rejection from the UHF receiver.
Adjusting VR1 too far anticlock-
wise will prevent successful repeater
operation.
VR2 should be set fully anticlock-
wise if you are using a single repeater.
If you are using multiple repeaters, set
VR2 on all repeaters fully clockwise,
giving a 12.5s delay. If your transmitter
can send signals more often than this,
you will need to experiment with the
maximum clockwise rotation of VR2
that will still cause all valid packets
to be relayed.
Remember that the settings for the
VR1 and VR2 trimpots are only read by
IC1 when first powered up and when
S1 is pressed. LED1 and LED2 light
when S1 is pressed, to acknowledge
that the settings have been updated.
Once you’ve finished adjusting
VR1 and VR2, you will need to check
whether the ultimate receiver is cor-
rectly decoding the retransmitted code
from the repeater(s). If not, you may
need to move them.
You can then permanently mount
the repeater(s). This is done using
the mounting holes provided in the
box corners.
These holes are accessible when the
box lid is removed.
Alternatively, you could use a brack-
et and attached this to the box using
the box mounting holes.
Avoid drilling extra holes in the box
as this could compromise its water-
tight seal. SCHere’s how it looks
mounted in its
waterproof
case. The blue
and yellow
wires are the
170mm-long
transmitting
and receiving
antennas –
they can be left
“floating” in the
case but ensure
there are no bare
ends to short to
any components or
to the PCB.