DKARS Magazine 201507

The Power Amplifier
The HamShield amplifier is a custom designed 250 milliwatt amplifier.
This provides plenty of power for line of sight communications,
as well as a high quality output for a variety of linear
amplifiers. We felt this was the perfect match for power consumption
on a small Arduino shield.
Here is an example Arduino sketch that transmits morse code
every 10 minutes, assuming the channel is not busy:
Audio Interfaces
The audio can be accessed two ways, both of which can be configured
to operate simultaneously:
Method 1: A built in TRRS jack that is compatible with nearly any
hands free cell phone headset. You can also use a TRRS "cross
over cable" to interface the audio to a laptop, tablet, or smartphone
for on-the-go analog and digital operations.
Method 2: The Arduino can be directly interfaced to the audio.
PWM output from the Arduino is smoothed and set to the
proper audio level for input into the radio transmitter. Audio
from the receiver is filtered and made available on an Arduino
ADC line. This allows for interesting applications such as data
and DTMF tone detection.
Data Interfaces
The HamShield uses the existing Arduino audio capability to
transmit and receive packet radio data, which is featured in our
HamShield library. While AFSK 1200 over FM is currently supported,
with some ingenuity, new data capabilities can be invented.
Test APRS transmissions from HamShield
Powering Your HamShield
Due to the amount of power required by the HamShield, it must
be connected to an external power supply. Care was taken to
make sure that the input voltage range was also within the output
range of several different types of battery technologies, including
4xAA battery packs and 7.4 volt LiPo battery packs. The
HamShield can operate between 5-30 volts DC, and is typically
powered by a 12 VDC power adapter.
As an added feature, the HamShield's power supply is also fed
into VIN on your Arduino. This means that the HamShield's
power supply, including connected batteries, will power your
Arduino and any other shields connected. Portable options, such
as APRS GPS trackers, hidden transmitter hunting, and laptop
APRS and packet radio are now possible.
The HamShield Arduino Library
The HAMShield Arduino library allows the user to control every
aspect of the radio. The library handles all communication between
the Arduino and the shield, so all you need to do is use
our simple API. We have also created functions for common
amateur radio modes, such as morse code, packet radio, SSTV,
scanning, white space channel seeking, empty channel detection,
and more! The capabilities of HamShield Library grow daily
as we close in on the HamShield shipping date.
Specifications
Form Factor
: Arduino-compatible stackable shield
Arduino Pins
: I2C; GPIO, PWM and ADC
Frequency RX/TX : 134-174MHz, 200-260MHz, 400-
520MHz
Amateur Radio Bands : 2 Meter, 1,25 Meter, 70 Centimeter
Power Output
: 250 milliwatts (preliminary)
Radio SoC
: Auctus A1846S
Channel Bandwidth : Selectable between 12,5KHz and
25KHz
Subaudio Modes : CTCSS, CDCSS (transmit/receive
independent)
Advanced Features : Volume, Squelch, VOX, DTMF
encode, DTMF decode, tail noise
elimination, tone generator, tone
detector, RSSI
Pre-Emphasis
: Can be disabled to assist with digital
modes
Antenna Connector : SMA, 50 Ohm (optional "rubber
duck")
Audio Connection : Hardware selectable between TRRS
(mobile phone style headset) and
Arduino PWM/ADC inputs and
outputs, PWM/ADC smoothing
filters built in
Input Voltage Range : 5-20VDC, 4xAA, 7,4 volt lithium
battery pack, power adapter capable
(requires external power supply as
Arduino does not supply enough
power for shield)
More references:
HamShield Quick Start Guide(Youtube)
Hamshield Github page
Hamshield on Kickstarter
DKARS Magazine, editie 13 -18- juli 2015