siliconchip.com.au Australia’s electronics magazine June 2019 91
shunts back to the E15 bridge module,
to switch the E32 module into Mode 0.
You need to do it in that order, because
the E32 module can be damaged if it’s
switched to Mode 0 before an antenna
is connected.
Selecting an antenna
If you’re not aiming for maximum
range, you could use one of the low-
cost ‘rubber ducky’ antennas with an
integrated 90° SMA plug on the bot-
tom, as shown in one of the photos. Go
for one of the longer ones if you can.
Alternatively, you could use one
of the longer ‘loaded whip’ antennas
fitted with a magnetic mounting base
and a 1.5m-long cable ending in an
SMA plug. These antennas are around
210mm long including the loading
coil, and are claimed to have an SWR
of less than 1.5 at 433MHz, together
with a gain of 3dBi.
However, this would not be legal to
use with the 25mW output power set-
ting as it would exceed the unlicensed
EIRP limit. You could only use it with
the 10mW power setting, which would
reduce power consumption but also
give you shorter range than the 25mW
setting with a quarter-wave whip.
Loaded whip antennas are availa-
ble from a few different suppliers on
the web, including Banggood, which
currently has them for about $5. En-
sure you get one fitted with a stand-ard SMA plug, not one with the more
common RP-SMA (reversed polarity)
plugs. The standard plug has a centre
pin to match the centre hole in the
module’s SMA socket.Connecting it to an Arduino
Using the E32-TTL-100 module
with an Arduino Uno or similar is
fairly straightforward, as you can see
from Fig.3.
An LM1117T-3.3 regulator is used to
derive the module’s 3.3V supply from
the Arduino’s 5V line, because when
it’s transmitting, the module can draw
peak currents of over 100mA, which
is too much for the Arduino’s onboard
3.3V regulator.Fig.4; connecting the E32 to a Micromite is nearly identical
to an Arduino except it doesn’t require two series 4.7kW
resistors on the RXD and TXD lines.Fig.3: connection diagram
for the E32 to an Arduino
Uno or similar.