achieve high sensitivity
levels using a low cost
crystal and associated low
cost glue components.
LoRa provides significant
advantages in both
blocking and selectivity
modulation techniques. A
block diagram of the
subsystems is represented
in Figure 1.
In addition to
servicing the PW1-928’s
SX1272 RF hardware, the PIC burns cycles that support
the high level protocol functions. Commands and data
flow between the SX1272 and PIC via an SPI portal.
Although the SX1272 speaks SPI, it is not equipped with a
native RS-232 compatible serial interface. So, the PW1-
928’s PIC is used by the SX1272 as an RS-232 to SPI
translator. The PW1-928 talks to the outside world on the
RF side via the SX1272. The PIC’s UART is used to transfer
data and commands in the digital hardware domain.
Figure 2 is a graphical depiction of the PW1-928 RF
data transceiver module’s I/O pin layout. The physical
dimensions come in handy when you are laying out your
printed circuit board (PCB) design that will incorporate the
PW1-928. You will also need the pinout information
contained within Table 1.
The contents of Table 1 tell us a bunch. The PW1-928
is a 3. 3 volt device. This power supply information helps
with the choice of host microcontrollers. In this case, we
know that if we plan to incorporate a five volt
microcontroller, we may need to add 3.3V to 5.0V
I/O logic level converters to the design.
In addition to the power supply information,
Table 1 says we will need a 3. 3 volt compatible
serial interface on our host device to drive the PW1-
928’s SI and SO pins. The PW1-928 SO pin is the
module’s serial output pin. In the case of the PW1-
928, the SO pin drives received data (RXD in RS-
232 lingo) from the radio subsystem. We should
connect the PW1-928’s SO pin to the host
microcontroller’s RS-232 serial port RXD pin.
The PW1-928’s SI pin is equivalent to a
microcontroller’s RS-232 TXD pin. Data from the
host microcontroller’s TXD pin drives the PW1-928’s
SI pin. Two independent 64-byte FIFO buffers are
placed in the PW1-928’s serial interface TX and RX signal
If necessary, we can also support a couple of transmit
and receive visual indicators using the PW1-928’s RXS and
TXS I/O pins. The PW1-928’s visual indication pins can
also be used as hardware handshake signals.
From experience, we will certainly provide a means of
externally resetting the PW1-928 via its n_RST signal.
Powering the PW1-928 and host microcontroller with a
battery will most likely mean that we will at some point
want to put the PW1-928 into low current mode. So, we’ll
plan for that in our design as well.
The PW1-928 can be forced into a low power standby
mode using the PW1-928’s STBY pin. In standby mode,
ADVANCED TECHNIQUES FOR DESIGN ENGINEERS
April 2017 55
■ FIGURE 1. The SX1272 is capable of speaking SPI but not RS-232 serial. The SX1272’s
RXTX pin is used to trigger an external RX/TX switch.
■ FIGURE 2. This is the template you will need to integrate
the PW1-928 RF data transceiver module into your design.
■ TABLE 1. Once your PW1-928 PCB pads are positioned, you can
use this table to string in the traces.