siliconchip.com.au Australia’s electronics magazine May 2019 49
and waiting for data. This is done by
switching off power to components
when they are not required.
The two trimpots, VR1 and VR2, are
only connected to the 5V supply when
their positions are being read. This is
done only during the initial power-
up process and when switch S1 is
pressed. Any other time, the RA6 and
RA7 pins that supply 5V to the trim-
pots are low (0V), to prevent current
flow through the pots. This saves 1mA,
which adds up to 24mAh per day.
Similarly, the transmitter (TX1) is
off until it is required to send a UHF
signal. TX1 is powered directly from
IC1’s RA2 and RA3 digital outputs
(pins 1 & 2); these go high (to 5V) to
power TX1. The power saving is con-
siderable since TX1 draws some 10mA
when powered and transmitting. This
saves 240mAh/day.
IC2 is on standby unless it is being
used. So unless there is a valid data
being received, it draws just 10μA in-
stead of the 10mA required when it is
active. Typically, the memory is only
powered twice as long as the transmit-
ter; the first half being the reception
period and the second half being the
transmission period. This also saves
around 240mAh/day.
Microcontroller IC1 typically draws
1.7mA and UHF receiver RX1 draws
2.9mA. The transmit and receive LEDs
are powered when TX1 and RX1 are ac-
tive respectively, and draw about 3mA.
The LEDs can be disconnected using
a jumper shunt (JP1) to save power if
they are not needed. They are mainly
provided for testing purposes.
The circuit is powered from a sin-
gle 600mAH LiFePO 4 cell. The quies-
cent current draw is around 9.4mA,
ie, when the transmitter, memory and
LEDs are off. This means the cell will
last for around 60 hours or 2.5 days
when fully charged.
Charging circuitry
The LiFePO 4 cell is charged by IC3,
which is powered from a 5V regula-
tor (REG1) and this, in turn, is pow-
ered from a solar panel. Note that it
connects to the circuit via a fuse (F1),
which prevents damage if the cell is
inserted incorrectly. If the cell is re-
versed, current will flow through di-
ode D2 and blow the fuse. Diode D1
prevents damage if the solar panel is
accidentally connected with the wrong
polarity.
IC3 is a miniature single-cell inte-
Parts list – 433MHz Wireless Data Repeater
1 double-sided PCB coded 15004191, 103.5 x 78mm
1 IP65 enclosure, 115 x 90 x 55mm [Jaycar HB6216]
1 600mAh LiFePO 4 cell (AA sized, ie, 50mm diameter, 14mm long) [Jaycar SB2305]
1 12V 5W Solar panel [Jaycar ZM9050]
1 panel label (see text)
1 25 x 15 x 10mm powdered iron toroid (L1) [Jaycar LO1242]
1 433MHz ASK transmitter (TX1) [Altronics Z6900, Jaycar ZW3100]
1 433MHz ASK receiver (RX1) [Altronics Z6905, Jaycar ZW3102]
1 PCB-mount tactile momentary SPST pushbutton switch (S1)
[Altronics S1120, Jaycar SP0600]
1 2-way screw terminal with 5.08mm spacing (CON1)
1 2-pin header, 2.54mm spacing (JP1)
1 3-pin header, 2.54mm spacing (JP2)
2 shorting blocks/jumper shunts (JP1,JP2)
1 1A M205 fuse (F1)
2 PCB-mount M205 fuse clips (F1)
1 18-pin DIL IC socket (for IC1)
1-2 8-pin DIL IC sockets (optional; for IC2 & REG2)
1 PCB-mount AA cell holder
1 flag heatsink, 19 x 19 x 9.5mm [Altronics H0630, Jaycar HH8502]
1 IP65 cable gland to suit 3-6.5mm diameter cable
6 PC stakes (optional)
4 M3 x 5mm panhead machine screws
1 M3 x 6mm panhead machine screw
1 M3 hex nut
2 4.75mm long #0 panhead self-tapping screws
2 100mm cable ties
1 500mm length of 1mm diameter enamelled copper wire
2 175mm lengths of medium-duty hookup wire OR
2 175mm length of 1mm diameter enamelled copper wire (see text)
Semiconductors
1 PIC16F88-I/P 8-bit microcontroller programmed with 1500419A.HEX (IC1)
1 23LCV1024-I/P 128kB SRAM in PDIP package (IC2) [Mouser, Digi-Key] OR
1 23LCV1024-I/SN 128kB SRAM in SOIC package (IC2) [Mouser, Digi-Key]
1 MCP73831T-2ACI/OT single cell Li-ion/LiFePO 4 charger, SOT-23-5 (IC3)
[Mouser, Digi-Key]
1 TL499A power supply controller (REG2) [Jaycar Cat ZV1644]
1 7805 5V regulator (REG1)
1 1N4004 1A diode (D1)
1 1N5404 3A diode (D2)
1 Green 3mm high-brightness LED (LED1)
1 Red 3mm high-brightness LED (LED2)
1 Yellow 3mm high-brightness LED (LED3)Capacitors
2 470μF 16V low-ESR electrolytic
1 100μF 16V electrolytic
1 10μF 16V electrolytic
1 470nF 63V MKT polyester (code 0.47, 474 or 470n)
1 220nF 63V MKT polyester (code 0.22, 224 or 220n)
2 100nF 63V MKT polyester (code 0.1, 104 or 100n)
1 100nF multi-layer ceramic
1 10nF 63V MKT polyester (code 0.01, 103 or 10n)
Resistors (all 0.25W, 1% metal film)
3 10kΩ (brown black orange brown or brown black black red brown)
4 1kΩ (brown black red brown or brown black black brown brown)
1 330Ω (orange orange brown brown or orange orange black black brown)
2 10kΩ miniature horizontal mount trimpots (VR1,VR2)
1 50kΩ miniature horizontal mount trimpot (VR3)