Wegmatt dAISy FeatherWing User manual

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WEGMATTLLC dAISy FeatherWing AIS Receiver
Contents
1Disclaimer ..................................................................................................................................3
2Introduction ...............................................................................................................................3
3Pinout ........................................................................................................................................4
3.2 Power............................................................................................................................................5
3.3 Serial 1...........................................................................................................................................5
3.4 Serial 2...........................................................................................................................................6
3.5 I2C .................................................................................................................................................6
3.6 GPIO ..............................................................................................................................................6
3.7 Antenna connector .......................................................................................................................6
4Interfaces...................................................................................................................................8
4.1 I2C .................................................................................................................................................8
4.1.1 Read/Write Operation ..........................................................................................................8
4.1.2 Device Address......................................................................................................................8
4.1.3 Register Layout .....................................................................................................................8
4.1.4 NMEA message stream.........................................................................................................8
4.2 GPIO ..............................................................................................................................................9
4.2.1 Overview ...............................................................................................................................9
4.2.2 None......................................................................................................................................9
4.2.3 Reset .....................................................................................................................................9
4.2.4 Sleep......................................................................................................................................9
4.2.5 LNA........................................................................................................................................9
4.2.6 AIS message ........................................................................................................................10
4.2.7 I2C data ...............................................................................................................................10
5Using the dAISy FeatherWing....................................................................................................11
5.1 Interpreting the status LEDs .......................................................................................................11
5.2 Configuration and debug menu..................................................................................................12
6Tips for good AIS reception .......................................................................................................14
6.1 Antenna.......................................................................................................................................14
6.2 Location, location, location.........................................................................................................14

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6.3 Radio frequency noise ................................................................................................................15
7Troubleshooting .......................................................................................................................15
8Specifications ...........................................................................................................................16
9Source code and schematics......................................................................................................17
10 Contact.................................................................................................................................17

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1Disclaimer
dAISy FeatherWing is a reliable, dual-channel AIS Receiver. However, under no circumstances should
it be solely relied on for collision avoidance or navigation. It’s the user’s responsibility to use the
product prudently. Neither Wegmatt LLC nor its dealers accept responsibility or liability to the product
user or their estate for any accident, loss, injury, or damage whatsoever arising out of the use of this
product.
2Introduction
The dAISy FeatherWing is a dual-channel AIS receiver with integrated low-noise amplifier (LNA). Thanks
to its small size and low power consumption the dAISy FeatherWing is ideally suited for embedded
applications.
AIS (automatic identification system) is an automatic tracking system for ships. Ships broadcast their
position and other information over VHF
1
. The dAISy FeatherWing allows you to receive these
transmissions, enabling real-time tracking of nearby vessels.
The dAISy FeatherWing outputs the AIS data as a stream of ASCII messages, which are encoded in a
marine standard format known as AIVDM sentences
2
. This format is understood by applications and
devices like chart plotters
3
, marine traffic aggregators
4
, and can be processed by many opensource
libraries
5
.
While the dAISy FeatherWing is designed to be mounted directly on top of any Adafruit Feather
development board, it can also be used with other microcontrollers and single board computers.
1
https://en.wikipedia.org/wiki/Automatic_identification_system
2
https://gpsd.gitlab.io/gpsd/AIVDM.html
3
https://opencpn.org
4
https://www.aishub.net, https://www.marinetraffic.com, …
5
https://pypi.org/project/simpleais, https://pypi.org/project/libais, https://github.com/schwehr/libais, …

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3Pinout
The pinout of the dAISy FeatherWing is compatible with the Adafruit Feather Specification
6
.
Figure 1: Bottom view of dAISy FeatherWing
The table below lists all pins and their function. All other pins are not connected to any part of the
circuit. For a detailed description of a pin functionality see respective section in this chapter.
Note that all communication pins are 3.3 V only!
Pin
Function
Feather
Notes
3V3
3.3V power input
3.3V
GND
Ground
GND
RX1
Serial 1 RX input
TX
always enabled, 38400 bps fixed
TX1
Serial 1 TX output
RX
always enabled, 38400 bps fixed
RX2
Serial 2 RX input
-
configurable, disabled by default
TX2
Serial 2 TX output
-
configurable, enabled by default at 38400 bps
SCL
I2C clock
SCL
configurable, enabled by default
SDA
I2C data
SDA
configurable, enabled by default
IO1
GPIO 1
D12
configurable I/O function, default off
IO2
GPIO 2
D13
configurable I/O function, default off
RST
Reset
-
Used for factory programming
TST
Test
-
Used for factory programming
Table 1: dAISy FeatherWing pinout
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https://learn.adafruit.com/adafruit-feather/feather-specification

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3.2 Power
Power for the dAISy FeatherWing is supplied through the 3V3 and GND pins. The pins align with 3.3V
and GND pins of the Adafruit Feather.
dAISy
Feather
3V3
3.3V
GND
GND
Table 2: Power pinout
The dAISy FeatherWing is a 3.3V device. Applying a voltage higher than 3.3V will damage the dAISy
FeatherWing!
In regular operation the dAISy FeatherWing draws 70 mA of current, equivalent to 230 mW of power.
The built-in low-noise amplifier (LNA) can be disabled to reduce power consumption, with the trade-off
of reduced AIS range.
The dAISy FeatherWing can also be put into a low power sleep mode, which turns off AIS reception.
Mode
Current
Power
LNA enabled (default)
70 mA
230 mW
LNA disabled
35 mA
115 mW
Sleep
0.35 mA
1.15 mW
Table 3: Power consumption
3.3 Serial 1
Serial 1 is the primary communication interface of the dAISy FeatherWing. The pins are labelled RX1/TX1
and align with the TX/RX pins of the Adafruit Feather (Serial1 in Arduino).
dAISy
Feather
RX1
TX
TX1
RX
Table 4: Serial 1 pinout
Serial 1 is always enabled and uses 3.3V UART signaling at a fixed speed of 38400 bits per second.
Baud rate
38400 fixed
Data bits
8
Parity
None
Stop bits
1
Flow control
None
Table 5: Serial 1 interface parameters
When in receive mode, the dAISy FeatherWing will output AIS messages as NMEA AIVDM sentences
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.
Depending on the configuration, the output may include additional debug messages with information
like signal strength or data errors.
Sending the ESC character (0x1B) on Serial 1 will bring up the configuration menu.
7
https://gpsd.gitlab.io/gpsd/AIVDM.html

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3.4 Serial 2
Serial 2 is a configurable UART interface. The pins are labelled RX2/TX2 and are not aligned with the
standard pinout of Adafruit Feathers.
Serial 2 can be configured as NMEA output (default), NMEA input, or disabled. Speed is configurable to
4800, 9600 and 38400 bits per second.
Baud rate
4800, 9600, 38400
Data bits
8
Parity
None
Stop bits
1
Flow control
None
Table 6: Serial 2 interface parameters
When configured as NMEA output, Serial 2 will output NMEA AIS sentences.
When configured as NMEA input, all NMEA messages received on Serial 2 will be forwarded to Serial 1.
One application for this mode is to add GPS data to the AIS data stream.
3.5 I2C
The I2C pins are labelled SDA/SCL and align with SDA/SCL pins on the Adafruit Feather (Wire in Arduino).
The I2C address is configurable, with a default value of 0x33.
dAISy
Feather
SDA
SDA
SCL
SCL
Table 7: I2C pinout
The dAISy FeatherWing includes 10K pull-up resistors on the SDA and SCL lines.
See chapter 4.1 for a detailed description of the I2C interface.
3.6 GPIO
IO1 and IO2 are configurable input/output pins. The pins are labelled IO1/IO2 and align with D12/D13
pins on the Adafruit Feather (digital pins 12 and 13 in Arduino).
dAISy
Feather
IO1
D12
IO2
D13
Table 8: GPIO pinout
By default, no function is enabled, and the IO pins are disconnected.
See chapter 0 for a detailed description of the configurable GPIO functionality.
3.7 Antenna connector
The edge-mount antenna connector of the dAISy FeatherWing is a female SMA connector with standard
polarity.

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The dAISy FeatherWing is matched for an antenna with an impedance of 50 ohms, which is standard for
marine VHF communication.

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4Interfaces
4.1 I2C
4.1.1 Read/Write Operation
The dAISy FeatherWing supports the I2C protocol with 7-bit device address, followed by the R/W bit.
For a write operation, the first byte sent is the register address byte. The next byte sent is written to
that address. The register address is automatically incremented after each byte sent, until the address
reaches 0xff.
To read a register, first write the register address, then use the I2C read operation to access the register
data. The register address is automatically incremented after each byte is read, until the address reaches
0xff.
4.1.2 Device Address
By default, the I2C device address of the dAISy FeatherWing is 0x33.
The I2C address can be configured in the range from 0x30 to 0x3f.
4.1.3 Register Layout
Currently all registers are read-only. Writes to the registers will be ignored.
Address
7
6
5
4
3
2
1
0
0x00
Device type (12 for dAISy FeatherWing)
0x01
Firmware version major
0x02
Firmware version minor
..
0xfd
Number of bytes available (high byte)
0xfe
Number of bytes available (low byte)
0xff
NMEA message stream
Table 9: I2C register map
4.1.4 NMEA message stream
If I2C is enabled, AIS NMEA messages can also be read over I2C.
The currently available number of bytes in the message stream can be read at addresses 0xfd and 0xfe.
The register at address 0xff allows the message stream to be read. If data is available, successive reads
of register 0xff will return the waiting message data. If there’s no data available, or if reading more bytes
than available, the value 0xff will be returned.
When reading the NMEA message stream over I2C, it is recommended to use a polling interval of 100ms
or shorter/faster. Longer/slower polling intervals may result in invalid or missed NMEA messages due to
an overflow of the internal 512 bytes FIFO buffer.

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4.2 GPIO
4.2.1 Overview
The functionality of pins IO1 and IO2 of the dAISy FeatherWing is configurable.
The following functions are available:
Function
Electrical
Low
High
None (default)
Not connected
Reset
Input, pull-down
Pulse high for > 100 ms to trigger reset
Sleep
Input, pull-down
Receiver active
Sleep
LNA
Input, pull-down
LNA disabled
LNA enabled
AIS message
Output
Positive pulse when AIS msg received
I2C data
Output
No I2C data
I2C data available
Table 10: GPIO pin functions
4.2.2 None
By default, IO pins are disabled. To minimize power consumption in sleep mode, it is recommended to
either assign a function to all IO pins, or connect unused IO pins to GND.
4.2.3 Reset
With this function enabled, the selected IO pin is an input that can be used to reset the dAISy
FeatherWing.
In regular operation, the input is held low. A reset is triggered by setting the input high for longer than
100ms, and then setting the input low.
The startup time from reset to receiving AIS messages is 600 ms.
4.2.4 Sleep
With this function enabled, the selected IO pin is an input that controls the sleep mode of the dAISy
FeatherWing.
When the input is low, the AIS receiver is active.
When the input is high, the AIS receiver is stopped and enters the low power sleep mode.
In sleep mode, the power consumption is less than 0.35 mA. The wake-up time from exiting sleep mode
to receiving AIS messages is approximately 50 ms.
4.2.5 LNA
With this function enabled, the selected IO pin is an input that controls the low-noise amplifier (LNA) of
the dAISy FeatherWing.
When the input is low, the LNA is turned off.
When the input is high, the LNE is turned on.
Switching the LNA off reduces power consumption by approximately 35 mA. The downside is a shorter
range of the AIS receiver.

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4.2.6 AIS message
With this function enabled, the selected IO pin will output a positive pulse when a valid AIS message is
received. Typical applications include waking up the Feather when new AIS messages arrive, or driving
an LED indicating when valid AIS messages are received.
The length of the pulse depends on the size of the AIS message and typically ranges from 400 to 1200
us. Minimum time between two pulses is 30 us.
The falling edge of the pulse happens after the AIS message data is stored in the output buffers of the
serial and I2C interfaces.
For the serial interface, while the transmission of data may already start before the falling edge, the first
byte of the AIS message won’t be available from the Feather’s serial peripheral until the full byte is
received.
For the I2C interface, the complete AIS message will be available in the I2C buffer at the time of the
falling edge.
4.2.7 I2C data
With this function enabled, the selected IO pin will be high when data is available to be retrieved
through the I2C interface. The IO pin will be low if no I2C data is available or if the I2C interface is
disabled.
In case of an empty I2C output buffer, the rising edge of this signal occurs after a complete AIS message
is stored in the buffer. The falling edge occurs after the last data byte is put onto the I2C bus, which may
be before the last byte is available from the Feather’s I2C peripheral.