siliconchip.com.au Australia’s electronics magazine May 2019 51
age between 1.20V to 1.32V, depending
on the particular IC. So VR3 makes it
adjustable, to allow the output voltage
to be set accurately.
Chaining multiple repeaters
As mentioned in the features pan-
el, it is possible to have more than
one repeater, to extend the transmis-
sion range further. The repeater clos-
est to the source (original transmitter)
will send the signal on to the second
repeater. When the second repeater
sends out its signal, the first repeater
must ignore it; otherwise the two re-
peaters will endlessly retransmit the
same packet.
This is prevented by an adjustable
delay between the end of each trans-
mission and the unit accepting a new
packet. This delay ranges from 50ms
to 12.5s and is set using VR2. The volt-
age at TP2 indicates the delay setting,
with each volt representing 2.5s. So for
example, if VR2 is adjusted for 2V at
TP2 then the delay is 2.5s x 2 = 5s. 0V
gives a 50ms (minimum) delay.
Construction
The repeater is built using a dou-
ble-sided PCB coded 15004191 which
measures 103.5 x 78mm. It fits in an
IP65 sealed box measuring 115 x 90 x
55mm. Use the PCB overlay diagram,
shown in Fig.3, as a guide during as-
sembly.
Start by soldering the battery charg-
er, IC3. This is in a small five-pin SMD
package. The correct orientation is evi-
dent since it has two pins on one side
and three on the other. Tack solder
one of the pins (ideally, at upper right)
then check its orientation and solder
the diagonally opposite pin.
Then proceed to solder the remain-
ing pins, and refresh the first joint with
a bit of added solder or flux gel.
If you accidentally bridge the three
pins which are close together, add a
little flux paste and then clean up the
bridge with the application of some
solder wick.
The PCB has the option to use a DIP
(through-hole) or SOIC (SMD) package
for the memory chip (IC2). Only one
type should be installed. If using the
SOIC package, solder it next, using a
similar procedure as described above.
But first, make sure that its pin 1 dot
or divot is at upper left, as shown in
Fig.3. It should also have a bevelled
edge on the pin 1 side.
The SOIC package for IC2 is larger
than that of IC3, so you should find it
a little easier. Again, any accidental
bridges can be cleaned up with flux
paste and solder wick.
Install the resistors next. They are
colour coded with the resistance val-
ue as shown in the parts list. A digi-
tal multimeter should also be used to
check the resistor values, as the colour
codes can be hard to read.
Fit the diodes next, making sure
to insert them with the correct polar-
ity, ie, with the striped ends facing as
shown in the overlay diagram. D2 is
considerably larger than D1.
We recommend soldering an IC
socket for IC1. The remaining ICs (in-
cluding IC2, if using the DIP package
version) can be fitted via an IC socket
or soldered directly in place, which
would give better long-term reliabil-
ity. Take care with orientation when
installing the socket(s) and ICs. Addi-
tionally, make sure that IC2 and REG2
are not mixed up.
Next, there are six optional PC
stakes to install. These make wiring
connections and test point monitor-
ing easier. These are located at TP5V,
GND, TP1, TP2 and one each for the
antenna connection of RX1 and TX1.
The capacitors should be mounted
next, starting with the 100nF multi-
layer ceramic capacitor next to UHF
receiver RX1, then following with the
MKT polyester types, none of which
are polarised. Follow these with the
electrolytic types, which must be in-
stalled with the polarity shown; the
longer lead goes into the pads marked
with a “+” sign, towards the top of
the PCB.
REG1 can be now fitted. It is mount-
ed horizontally on a heatsink. Bend the
leads so they fit the PCB holes while
the mounting hole lines up with the
hole on the PCB. Sandwich the heat-
sink between the regulator and PCB
and do up the screw and nut before
soldering the leads.
Trimpots VR1 to VR3 are next. VR1
and VR2 are 10kΩ and would typical-
ly be marked with 103. VR3 is 50kΩ
and may be marked as 503. Then in-
stall the LEDs, LED1 to LED3. In each
case, the anode (longer lead) goes to
the pad marked with an “A” on the
PCB. The bottom of the LEDs should
be about 5mm above the PCB surface
when soldered in place. You can
then fit pushbutton switch S1.
Install the 3-way and 2-way SIL
headers now, for JP1 and JP2. Thenfit the 2-way screw terminal, CON1,
with the wire entry holes end toward
the bottom PCB edge.
L1 is wound using 17 turns of 1mm
enamelled copper wire on a 25mm di-
ameter powdered iron toroidal core.
These turns should be wound neat-
ly around the perimeter, as shown in
Fig.3. Remove the enamel from the
ends of the wires using a hobby knife
so you can tin them and then solder
them to the PCB pads shown. The core
is held in place with two cable ties that
loop through PCB holes, as shown.
The battery holder must be orien-
tated as shown (red wire to +) and se-
cured to the PCB using two self-tap-
ping screws through the cell holder
and into the slotted holes on the PCB.
Cut the wires from the battery short
and terminate them to the PCB.
Insert the fuse clips for F1, making
sure that the end stops in the clips are
facing to the outside. Before soldering
them, insert the fuse so that the clips
are correctly aligned, for good contact
with the fuse.
Finally, the UHF transmitter and
receiver can be mounted. These must
also be orientated correctly. The pin
markings are printed on the transmit-
ter module. Orientate the antenna pin
connection on the transmitter and re-
ceiver so that they are adjacent to the
antenna connections on the PCB.
You have two options for the an-
tennas: either use 170mm lengths of
hookup wire coiled inside the box or,
for better range (>40m), 170mm-long
lengths of stiff enamelled copper wire
protruding from the box.
The extra 5mm in the lengths spec-
ified in the parts list is to give you
enough wire to solder to the antenna
terminals (for the hookup wire) or to
bend over at the tip (for the enamelled
copper wire).
Having chosen which antenna wire
you want to use, cut the appropriate
lengths and solder them to the antenna
PC stakes, or directly to the antenna
pads if you are not using PC stakes.
Note that you will need to scrape
some insulation off the end of the
enamelled copper wire (eg, with a
hobby knife) so that you can tin and
then solder it to the board.Mounting it in the box
There is not much work required to
mount the board in the box. We drilled
a hole in the side for the cable gland
required for the solar panel wiring.