88 Silicon chip Australia’s electronics magazine siliconchip.com.au
C
onnecting a couple of computers,
Arduinos, Micromites or other
micros via a UHF wireless data link
is easy if you use a pair of low-cost
modules based on the SX1278 ultra-
low-power LoRa modem/transceiver
chip. The SX1278 is made by Semtech
Corporation of Camarillo, Southern
California, which acquired the pat-
ented LoRa technology from French
firm Cycleo in 2012.
The name “LoRa” is a contraction
of “Long Range”. It is a wireless tech-
nology developed to enable low pow-
er wide-area networks (LPWANs) for
machine-to-machine (M2M) and In-
ternet of Things (IoT) applications.
The exact details of the technology
are proprietary and closed, but it’s
apparently based on spread-spectrum
modulation.
The SX1278 is designed to operate
in the UHF spectrum between 410 and
525MHz. This makes it suitable for
use in the 433.05-434.79MHz ISM (In-
dustrial, Scientific and Medical) band
which is available for license-free use
in most countries. In Australia, this is
called the LIPD (Low Interference Po-
tential Devices) band.
The SX1278’s data sheet can be
found at siliconchip.com.au/link/aao3
Note that in Australia, the maximum
transmitter power (EIRP – equivalent
isotropically radiated power) for un-
licensed devices in the LIPD band is
25mW or +14dBm. Transceivers with
programmable output power will need
to be configured to stay under this limit
to remain legal.
There are two different SX1278-
based LoRa modules currently avail-
able. One is the RA-02, designed by
AI-THINKER, which is available from
Banggood (siliconchip.com.au/link/
aao7) and various other suppliers for
around $6.60 each. The other is the
E32-TTL-100 from eByte, also availa-
ble from Banggood (siliconchip.com.
au/link/aao8) and other suppliers for
around $13.50 each.
So the RA-02 is around half the cost
of the E32-TTL-100, and as you can see
from the photos, it’s also much smaller
at just 16.5 x 16 x 3mm compared with
34 x 21 x 4mm for the E32-TTL-100,
not including its SMA RF connector
or its 7-pin SIL header. But the RA-02
has some disadvantages, too.
One of these is that the RA-02 mod-
ule’s tiny PCB is designed to be sur-
face-mounted on another PCB. So in-
stead of providing a pair of 8-pin SIL
headers with standard 2.54mm pinspacings for power and control, it has a
row of eight semicircular indentations
along each side, with each one gold
plated to allow soldering to matching
pads underneath.
The spacing of the indentations
is 2mm, so they do not line up with
pads on the common 2.54mm (0.1-
inch) grid.
Many constructors would therefore
want to solder the module to an adap-
tor PCB, to bring all of the connections
out to a pair of 8-pin SIL headers.
Another less attractive aspect of
the RA-02 module is that its RF out-
put/input connector is the extremely
small U.FL-R-SMT coaxial type, with
an outer diameter of only 2mm.
You will need a matching U.FL-LP
plug to mate with it, which in most
cases, comes as part of a complete an-
tenna/cable assembly. It would not be
easy to fit such a tiny plug to an ex-
isting cable.
So the RA-02 module is probably
best suited for use in commercial type
applications, especially those which
will be assembled using automated
pick-and-place equipment.
On the other hand, the E32-TTL-100
module is more suited for breadboard-
ing, testing and manual assembly.Using Cheap Asian Electronic Modules by Jim Rowe
This month we’re looking at two LoRa
modules based on the SX1278, a
complete wireless data modem/
transceiver capable of data rates
up to 300kbit over modest distances
in the 434MHz band. These can be
controlled from a micro using an SPI
or UART serial interface.434MHz LoRa
Transceivers