Wegmatt dAISy HAT AIS User manual
WEGMATTLLC dAISy HAT AIS Receiver
Contents
1Disclaimer ..................................................................................................................................2
2Configuring the Raspberry Pi for the dAISy HAT...........................................................................2
2.1 OpenPlotter...................................................................................................................................2
2.2 Raspberry Pi OS and Raspbian ......................................................................................................2
2.3 Configuration in OpenCPN............................................................................................................3
2.4 Connecting dAISy with other software.........................................................................................5
3Using the dAISy HAT ...................................................................................................................6
3.1 Interpreting the status LEDs .........................................................................................................6
3.2 Configuration and debug menu....................................................................................................7
4Using the breakout connections..................................................................................................9
4.1 Raspberry Pi I/O header................................................................................................................9
4.2 Serial 1 header ..............................................................................................................................9
4.3 Serial 2 header ............................................................................................................................10
4.4 I2C header...................................................................................................................................10
4.5 Debug header..............................................................................................................................10
4.6 RF connectors..............................................................................................................................11
5Tips for good AIS reception .......................................................................................................12
5.1 Antenna.......................................................................................................................................12
5.2 Location, location, location.........................................................................................................12
5.3 Radio noise..................................................................................................................................12
6Troubleshooting .......................................................................................................................14
7Specifications ...........................................................................................................................15
8Source code and schematics......................................................................................................16
9Contact ....................................................................................................................................16
Wegmatt LLC
6356 138th Ave NE #212
Redmond, WA
United States of America
https://wegmatt.com
Designed and assembled in USA
1Disclaimer
dAISy HAT is a reliable, dual-channel AIS Receiver. However, under no circumstances it should 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.
2Configuring the Raspberry Pi for the dAISy HAT
The dAISy HAT communicates with the Raspberry Pi through the serial port broken out one the
Raspberry Pi’s expansion header. Out-of-the-box, the Raspberry Pi uses these pins for other purposes
like a serial terminal or Bluetooth.
Reconfiguring serial ports is straight forward with recent versions of Rasperry Pi OS (since ca. late 2016)
and OpenPlotter. Configuration can be more complex with old version of Rasperry Pi OS or OpenPlotter,
especially on the Raspberry 3.
For beginners, we recommend starting with a new image of Rasperry Pi OS or OpenPlotter.
2.1 OpenPlotter
To use the dAISy HAT with OpenPlotter, follow the instructions in the official documentation. The dAISy
HAT is covered in the section Serial > Connecting the dAISy HAT
https://openplotter.readthedocs.io/en/latest/serial/connectingdAISy.html
2.2 Raspberry Pi OS and Raspbian
If you are running Rasperry Pi OS or Raspbian without OpenPlotter, use the raspi-config tool to
configure the serial port through which the Raspberry Pi talks to the dAISy HAT.
Open a terminal window on your Raspberry Pi and type:
sudo raspi-config
This will launch the Raspberry Pi Software Configuration Tool. Then enable the serial port by navigating
through the following steps:
Then enable the serial port by navigating through the following steps:
3 Interface Options -> I5 Serial Port
-> <No>(no login shell on serial) -> <Yes>(enable serial hardware) -> <Ok>
-> <Finish> -> <Yes>(reboot)
After completing the reboot, AIS data is available using the following parameters:
Serial port
/dev/ttyAMA0
Baud rate
38400
Data bits
8
Parity
None
Stop bits
1
Flow control
None
Use this information to configure OpenCPN or other programs. Keep in mind, that only one application
at a time can consume serial data.
You can verify the serial connection with a serial terminal program like for example screen. You may
have to install screen first by running:
sudo apt-get install screen
With screen installed, connect to the dAISy HAT with
screen /dev/ttyAMA0 38400
If the serial port is properly configured, pressing ESC will bring up the configuration and debug menu.
Pressing ESC again will return dAISy into receive mode. Exit screen by pressing CTRL-A, release the keys,
then press K (kill connection) and then Y to confirm.
2.3 Configuration in OpenCPN
OpenCPN is a free chart plotter and navigation software. Among many other things, OpenCPN supports
input from AIS receivers to display the position of ships on its charts.
You can learn more about OpenCPN on https://opencpn.org
If you are using OpenCPN as part of OpenPlotter, you can ignore this chapter. OpenPlotter already set
everything up for you.
There are several tutorials on the web on running OpenCPN on a Raspberry Pi. The consensus is, that
you should only attempt this on a Raspberry Pi 3 or 4 with an up-to-date version of Raspberry Pi OS. The
official instructions can be found here for Raspberry Pi 3:
https://opencpn.org/wiki/dokuwiki/doku.php?id=opencpn:opencpn_user_manual:getting_started:open
cpn_installation:raspberrypi_rpi2
and Raspberry Pi 4:
https://opencpn.org/wiki/dokuwiki/doku.php?id=opencpn:opencpn_user_manual:getting_started:open
cpn_installation:rpi4
Alternatively, users have reported good results by following this procedure:
https://www.agurney.com/raspberry-pi/pi-chart
Once OpenCPN is running on the Raspberry Pi, configure it for the dAISy HAT. Go to the Options dialog,
select the Connections icon and add a new connection. Set Properties to Serial. Enter or select
the Dataport under which dAISy presents itself (see chapters above to determine the correct port
name). Set Baudrate to 38400. Leave everything else as preset by OpenCPN.
Configuration of a serial connection for dAISy in OpenCPN
2.4 Connecting dAISy with other software
dAISy presents itself to computers as a serial port. See the configuration chapters above about
installation to learn how to determine the serial port.
The serial communication parameters of dAISy are:
Baud rate
38400
Data bits
8
Parity
None
Stop bits
1
Flow control
None
Depending on the software dAISy is used with, some or all parameters must be configured. For details,
please refer to the instruction manual of the respective application.
3Using the dAISy HAT
Using the dAISy HAT is as simple as connecting it with an antenna and a PC and powering up your AIS
capable application of choice. When plugged in, dAISy automatically starts to listen for AIS
transmissions.
3.1 Interpreting the status LEDs
The dAISy HAT has two two-color status LED, giving us some indication about how it’s feeling. Each LED
represents one of the two AIS channels.
Short GREEN flash every 5 seconds
dAISy is well and alive and in receive mode.
While in receive mode, the mode dAISy starts in when powered up, it will very briefly blink green every 5
seconds to indicate that everything is ok.
Long GREEN flash
Yay! dAISy received a valid AIS packet.
For every packet received and passing all error checks, the LED will turn green for ¼ second. At the same
time, dAISy will send the received message to the Raspberry Pi.
Long RED flash
dAISy received an invalid packet.
dAISy caught the start of a package, but the received data did not pass other sanity checks like encoding
standard or checksum. It might be a ship just out of range, interference from another radio source, or
just random noise.
Don’t panic, you will see a lot of red even under optimal conditions.
RED turned on permanently
dAISy failed to initialize the radio IC.
Shut down the Raspberry Pi and remove power. Plug it in again and see if this resolves the problem. If
the condition persists, there might a hardware issue with your device. Please contact us.
Fast regular blinking RED
dAISy encountered an unexpected system error.
Shut down the Raspberry Pi and remove power. Plug it in again and see if this resolves the problem. If
the condition persists, there might a hardware issue with your device. Please contact us.
No LED activity
The dAISy HAT may not receive power. Shutdown the Raspberry Pi and remove power. Then visually
inspect the expansion header and make sure that the dAISy HAT is properly seated on the Raspberry Pi.
Another possibility dAISy is not in receive mode because you were using the configuration menu.
Connect to dAISy with a serial terminal and press ESC. A message should tell you that it entered AIS
receive mode and the green LED should start to blink every 5 seconds.
Another possibility is, that dAISy failed to boot or crashed. In this case, shut down the Raspberry Pi and
remove power. Plug it in again and see if this resolves the problem.
If the condition persists, there might a hardware issue with your device. Please contact us.
3.2 Configuration and debug menu
When connecting to dAISy with a serial terminal (for example screen), pressing ESC will bring up a menu
with a few configuration and debug options.
The most used options are:
0-3: Controls the Serial 2 header on the dAISy HAT. Pressing 1 enables the serial port with a speed of
4800 baud, 2 is for 9600 baud, and 3 is for 38400 baud. Pressing 0 turns Serial 2 off.
S: Selects the function of the Serial 2 header. There are two modes:
1. NMEA output: Output AIS messages, for example to a Bluetooth module, RS-422/NMEA0183
adapter, or a data logger.
2. NMEA input: Act as an input for NMEA messages, for example from a GPS module. All data
received through Serial 2 will be forwarded to the Raspberry Pi.
D: Toggles debug messages. When enabled and in AIS receive mode, signal strength and other
information about valid and invalid AIS packets will be displayed. It is normal to receive a lot of broken
packages as there always will be radio noise and ships just out of range. With some experience, you can
use the debug messages to analyze and improve reception issues.
#: Save current settings (serial, channel, reset and debug) as startup defaults. This is particularly useful
when you want to persist the settings for the auxiliary serial output.
ESC: Resume receiving AIS messages.
Other options:
N: Keep pressed to get an idea of the current noise level. -120 to -100 dBm is normal. dAISy will only be
able to receive valid packets roughly 15 dBm above that level, consistent reception 25+ dBm above
noise.
V: If valid packages were received, this gives a summary of the signal strength at which AIS messages
arrived (min, max, average).
T: Enter test mode. In this mode, dAISy outputs a test message every 5 seconds. You can enter your own
message or have it output a preprogrammed AIS message. This mode is useful when you want to test
dAISy but do not have AIS reception at your current location. You can exit test mode by pressing ESC or
power-cycling dAISy.
C: Configure the radios of the dAISy HAT to listen to specific AIS channels. The dAISy HAT has two radios,
which by default are configured to listen on channel A at 161.975 MHz and channel B at 162.025 MHz
respectively. The dAISy HAT also supports the less common “Long range AIS” channels at 156.775 and
156.825 MHz.
R: Enable or disable Reset via GPIO. When enabled, the Raspberry Pi can reset the dAISy HAT through
GPIO18 (pin 12 on the Raspberry Pi expansion header). To reset the HAT, set GPIO18 high for 150ms or
longer, then set GPIO18 back to low.
L: Enable or disable low power sleep via GPIO. When enabled, the Raspberry Pi can put the dAISy AIS
Receiver into a low power sleep state by setting GPIO17 high. In sleep state, the radios are turned off
and the AIS receiver pauses operation. Current consumption drops from approximately 35 mA to less
than 0.8 mA. Operation is resumed within 100ms from the time GPIO17 goes back to low. This feature
requires firmware version 5.11 or newer.
I: Enable or disable low power sleep via Serial IO. When enabled, the dAISy AIS Receiver can be put into
a low power sleep state by applying 3.3V to the IO pad on the Serial 1 or Serial 2 ports. In sleep state,
the radios are turned off and the AIS receiver pauses operation. Current consumption drops from
approximately 35 mA to less than 0.8 mA. Operation is resumed within 100ms from the time Serial IO
goes back to 0V. This feature requires firmware version 5.11 or newer.
B: Enter boot loader mode for firmware updates. dAISy exits this mode through power-cycling, after a
20 second timeout without further activity, or after completing firmware upgrade.
4Using the breakout connections
The dAISy HAT AIS Receiver breaks out several interfaces as unpopulated footprints for 0.1” headers.
All digital interfaces are 3.3V only.
4.1 Raspberry Pi I/O header
The dAISy HAT uses the following connections for its operation.
Raspberry Pi
dAISy
Pin 2, 5V
5V power, the AIS receiver will draw less than 35mA in operation
Pin 6, GND
Connected to the GND plane of the HAT
Pin 8, UART0_TXD
Serial data from Raspberry Pi to dAISy, 3.3V signal level, 38400 bps
Pin 10, UART0_RXD
Serial data from dAISy to Raspberry Pi, 3.3V signal level, 38400 bps
Pin 11, GPIO17
Input, 3.3V, normally low, set high to enter sleep mode, see section 3.2
Pin 12, GPIO18
Input, 3.3V, normally low, pulse high for 150ms to reset AIS receiver, see
section 3.2
4.2 Serial 1 header
The header Serial 1 exposes the primary serial
interface of the dAISy AIS Receiver. It is connected
in parallel with the serial interface of the Raspberry
Pi and offers the same data and functionality.
Serial 1 is always active and runs at 38400 baud. It
can be used to run the dAISy HAT standalone,
without being connected to a Raspberry Pi.
When connected to a Raspberry Pi, Serial 1 should
only be used to receive the same data as the
Raspberry Pi. Do not send data through the RX pin
while the HAT is connected to a Raspberry Pi.
The 5V pad is connected to the 5V power rail of the
Raspberry Pi. When the dAISy HAT is not connected
to the Raspberry Pi, the 5V pad can be used to power the AIS Receiver. When running standalone, the
dAISy HAT will draw a maximum current of 40mA in receive mode.
dAISy Serial 1
dAISy MCU
Raspberry Pi
Comment
5V
5V to 3.3V LDO
Pin 2, 5V
5V power rail of Raspberry Pi and HAT. Can
be used to power HAT standalone.
GND
GND
GND
Connected to the GND plane of the HAT
TX
Serial 1 TXD
Pin 10, UART0_RXD
Serial data out, 3.3V signal level, 38400 bps
RX
Serial 1 RXD
Pin 8, UART0_TXD
Serial data in, 3.3V signal level, 38400 bps.
Don’t use when HAT is connected to
Raspberry Pi.
IO
GPIO
-
I/O, 3.3V signal level, configurable to enter
sleep mode, see section 3.2
4.3 Serial 2 header
The header Serial 2 exposes the secondary serial interface of the dAISy AIS Receiver. This serial port is
controlled by dAISy’s MCU and not connected to the Raspberry Pi.
Speed and function of Serial 2 are configured in the debug menu. It can operate as secondary output or
as NMEA input. The pinout is compatible with the Adafruit Ultimate GPS module.
The 5V pad is connected to the 5V power rail of the Raspberry Pi. When the dAISy HAT is not connected
to a Raspberry Pi, the 5V pad can be used to power the AIS Receiver. When running standalone, the
dAISy HAT will draw a maximum current of 40mA in receive mode.
dAISy Serial 2
dAISy MCU
Raspberry Pi
Comment
5V
5V to 3.3V LDO
Pin 2, 5V
5V power rail of Raspberry Pi and HAT. Can
be used to power HAT standalone.
GND
GND
GND
Connected to GND plane of dAISy HAT
TX
Serial 2 TXD
-
Serial data out, 3.3V signal level,
configurable speed.
RX
Serial 2 RXD
-
Serial data in, 3.3V signal level, configurable
speed.
IO
GPIO
-
I/O, 3.3V signal level, configurable to enter
sleep mode, see section 3.2
4.4 I2C header
This header breaks out the I2C interface of the Raspberry Pi. This allows applications running on
Raspberry Pi to communicate with I2C sensors. For example, OpenPlotter supports temperature,
pressure, humidity and light sensors.
The I2C interface is independent of the AIS Receiver and the pads are directly connected to the
Raspberry Pi expansion header. For more information about the I2C interface, refer to the
documentation of the Raspberry Pi.
dAISy I2C
Raspberry Pi
Comment
3V3
Pin 1, 3V3
3.3V power from Raspberry Pi, 50mA max
current
SDA
Pin 3, SDA1 / GPIO2
I2C data, 3.3V signal level
SCL
Pin 5, SCL1 / GPIO3
I2C clock, 3.3V signal level
GND
GND
Connected to GND plane of dAISy HAT
4.5 Debug header
The debug header breaks out the debug and programming interface of the MCU controlling the AIS
receiver. The MCU is a Texas Instrument MSP430F5232.
The debug header also gives access to the 3.3V power rail of the AIS receiver, which can be used to
power peripherals. Maximum current available is 150mA. Recommended current for continuous
operation is 50mA. Back-powering the AIS receiver through the 3.3V pad is possible but may degrade RF
performance.
dAISy Debug
dAISy MCU
Raspberry Pi
Comment
GND
GND
GND
Connected to GND plane of dAISy HAT
TST
TEST / SBWTCK
-
TI SBW programming interface
RST
RST / SBWTDIO
-
TI SBW programming interface, reset
3V3
3V3
-
Connected to 3.3V rail of dAISy HAT. 150mA
max current, 50mA continuous.
4.6 RF connectors
The edge-mount antenna connector of the dAISy HAT is female SMA, standard polarity. There is also an
unpopulated footprint for a surface mount vertical MMCX connector, for example Molex 73415-2061.
The dAISy HAT is matched for an antenna with an impedance of 50 ohms, which is standard for marine
VHF communication.
5Tips for good AIS reception
dAISy is not the most sensitive AIS receiver out there. But you we can help it to excel with some basic
measures.
5.1 Antenna
If everything else is optimal, almost any antenna tuned to the VHF band will do. I used a simple wire cut
to length for my first prototypes. However, a good antenna will greatly improve results.
AIS messages are broadcast on two channels around 162 MHz, which is in the maritime VHF band. This
means that any antenna sold as “marine VHF antenna” will be a good start.
The short VHF “rubber duck” antennas are cheap and will work at short distance. As long as you check
whether 162 MHz is inside the supported frequency range, you can even ignore the “marine” and save a
few bucks. However, the more broadband the antenna, the worse the reception quality.
A step up are VHF whip antennas. These are steel rods about 1 meter (3.5ft) long. While bulky, these
don’t cost much more than the “rubber duck” but provide superior results. Personally, I use the TRAM
1600-HC which cost around US $40.
The AIS antenna should be separated as far as possible from the voice VHF antenna to avoid
unnecessary interference. The best separation is achieved by vertically separating the antennas or at
least mounting them on opposite sides of a vessel.
To avoid damaging dAISy’s receiver, the antenna should be mounted at least 3 meters away from, or at
least out of the transmitting beam, of high-power transmitters such as radars or other VHF antenna
installations.
IMPORTANT: Do NOT directly connect the dAISy HAT to the same antenna as your VHF radio, this will
damage the AIS receiver. To share an existing antenna with a VHF radio, use an ACTIVE splitter. Active
splitters protect the AIS receiver by automatically disconnecting it when the VHF radio is transmitting.
Several customers reported good results with the inexpensive Glomex RA201 VHF/AIS/Radio Splitter.
5.2 Location, location, location
Good AIS reception requires line of sight.
A few buildings and trees between you and your targets aren’t ideal, but you will still be able to catch a
few messages. Hills and mountains however are almost certain showstoppers. A clear view of the water
and your targets is ideal.
In my experience the most important factor is the height of the antenna above sea-level (or lake-, river-,
wherever-level the ships are). Sitting at the beach or on the deck of a boat will work. Mounting the
antenna on the mast of your boat or standing on the observation deck of a cruise ship is better. A hill
overlooking the harbor is great. Climbing that 2000m mountain that towers over the coast is AIS heaven.
In a nutshell: The farther you can see, the better.
5.3 Radio noise
The main weakness of dAISy, and probably most low-cost and SDR-based AIS receivers, is susceptibility
to radio noise. The effect of noise is reduced range and few successfully received packets.
Unfortunately, there’s not much we can do except finding a spot that’s less impacted by noise. Outdoors
is better than indoors (computers, power-supplies, wireless networks, ...). Countryside is better than
down-town (taxi radios).
dAISy has an integrated 12 MHz wide bandpass filter to reduce the impact of radio noise outside the 162
MHz target frequency. However, to keep cost and size down, the integrated filter is rather simple. A very
narrow-band antenna or an external bandpass filter can improve reception. Please report back any
results if you go down this route.
6Troubleshooting
Problem
Solution
No activity of the status LEDs
Verify that the dAISy HAT is properly seated.
Device in reception mode, but not valid AIS
messages received (no ¼ second green flashes)
Verify the antenna connection and location.
Good AIS reception requires line-of-sight, verify
your setup from a location that is certain to have
traffic, for example near a harbor.
Device indicates valid AIS messages (¼ second
green flashes), but no messages received on the
Raspberry Pi.
Verify that the serial port shows up, if not verify
the hardware configuration. Verify the serial
configuration of your software. Verify the serial
communication with a program like screen.
Software receives positions, but fewer than
expected and/or with worse range than
expected.
Verify the antenna connection and location.
Good AIS reception requires line-of-sight. Move
the antenna away from sources of electrical
noise.
After some time, dAISy indicates a device error
(fast blinking red LED)
This should not occur with the dAISy HAT. Power
cycle the Raspberry Pi to resolve the issue.
If a problem persists don’t hesitate to contact us.
7Specifications
Power
Power input ports
Raspberry Pi Header (RPi), Serial 1 & 2, Debug
header
Input voltage RPi / Serial 1 / Serial 2
5V
Input voltage Debug
3.3V
Input current RPi / Serial 1 / Serial 2 / Debug
< 35 mA
Input current in sleep mode
< 0.8 mA
Power output ports
Serial 1, Serial 2, Debug header
Output voltage Serial 1 / Serial 2
5V
Output voltage Debug
3.3V
Maximum output current Serial 1 / Serial 2
Limited by external 5V supply
Maximum output current Debug
150mA
Radio
Independent receivers
2
Frequency bands
161.975MHz, 162.025MHz, 156.775MHz,
156.825MHz
AIS channels
2, freely configurable
Bandpass filter
SAW 156.3 - 162.025MHz pass band
RF connector
SMA
Input impedance
50Ω
Data I/O
AIS message encoding
NMEA 0183 (!AIVDM)
Supported AIS message types
1-27
Serial speed RPi / Serial 1
38400 Baud fixed
Serial speed Serial 2
4800, 9600, 38400 Baud configurable
Serial protocol
8 data bits, no parity, 1 stop bit (8N1)
Serial mode RPi / Serial 1
NMEA out fixed
Serial mode Serial 2
NMEA out, NMEA in configurable
Serial signal voltage RPi
3.3V
Serial signal voltage Serial 1 / Serial 2
3.3V (5V tolerant)
Dimensions
Circuit board without connectors
65mm x 56mm
Circuit board with connectors
65mm x 66mm x 14mm (6mm w/o RPi conn)
Circuit board mounting holes
4x Size: 2.75mm (M2.5) Distance: 58mm x 49mm
See also: https://github.com/raspberrypi/hats/blob/master/hat-board-mechanical.pdf
Weight
Product
18g
w/o 40-pin Raspberry Pi header
14g
8Source code and schematics
Currently dAISy is only partially open source.
The core of dAISy, how the Silicon Labs Si4362 radio IC is programmed to receive AIS, is available on
Github. While the project does not include all the functionality of dAISy as sold, we do backport any bug
fixes that are relevant to the task of receiving AIS. https://github.com/astuder/dAISy
There is also a long thread on 43oh that documents the journey of dAISy from its humble beginnings.
https://forum.43oh.com/topic/4833-potm-daisy-a-simple-ais-receiver/
If you want to experiment with the real code, brick your device with custom firmware or even build your
own dAISy from scratch, contact us. Tinkerers welcome!
9Contact
Please don’t hesitate to contact us if you need support. We also love to hear about your projects and are
happy to share your related blog posts, videos, and pictures on our social media.
You can also reach us on GitHub, and Twitter.
https://wegmatt.com
Wegmatt LLC
6356 138th Ave NE, #212
Redmond, WA 98052
United States of America
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