This article describes our experience connecting an older-model AIS receiver to a modern Android-based tablet. With only a minimum investment (less than $40), crew on Inceptus can now view AIS targets on their Navionics charting app.
Chris Stask (Inceptus) provided the impetus for this article, volunteering his boat as a test subject and taking photos as we progressed. Bjarne Hansen (Hoku Pa’a) crafted this article and assembled the wires.
Unless a boat is factory-fresh, it will likely sport multiple generations of electronics, from the 1980s all the way to tablets and phones from this decade. This is challenging, since new gear often doesn’t speak the same language as older gear. How does one avoid the financial and environmental costs of discarding old but functioning gear, while still satisfying a desire for new bells and whistles? Here’s how we met the challenge of getting an AIS receiver from 2004 to talk to 2023 software, using communications protocols from the 1960s and 1997.
Those familiar with AIS can skip to the next section – otherwise, the following is a brief refresher about the Automatic Identification System.
AIS uses two VHF digital radio channels to periodically broadcast vessel data such as position, speed, and heading. Equipped with a suitable receiver, one can monitor AIS-transmitting vessels over distances of several miles or more, and this radio-based system transmits through fog and around land obstacles. Further, some shore stations use AIS to broadcast virtual nav-aids, without needing to have a physical object in the water. The following diagram illustrates how AIS functions. More details can be found at AllAboutAIS.com or in “Tips For Installing AIS On Your Boat”.
Though the AIS receiver is shown as separate from the other components, technological advances have produced combination devices, such as Standard Horizon’s GX2400GPS VHF radio with internal AIS Receiver and GPS. At about $650 (summer 2023). It is a very cost-effective way of obtaining AIS receive capability.
An AIS transceiver enables you to transmit your boat’s data to other vessels, while also receiving information from other boats. Why doesn’t every boat have a transceiver? There are many valid reasons: cost is one; another is waiting for technology to further advance, or avoiding the hassle of obtaining an MMSI number. Some folks even want to preserve their anonymity on the water.
What Pieces Are Needed?
For AIS receiving capability you need an antenna, a receiver, and a plotter:
- An antenna can be constructed inexpensively (see: “Build Your Own Inexpensive, Easy, High-Performance VHF/AIS Antenna”), or you can use a spare marine VHF antenna.
- A receiver can be picked up at low cost from boat owners who are replacing their receive-only units with transceivers. We obtained a free Smart Radio SR-161 receiver from a fellow sailor who had installed a new transceiver (thanks Cookie Cutter!). The SR-161 is an older piece of kit – launched in 2004 – but it is well-designed, has good performance, and should last decades if treated well.
- Instead of a dedicated plotter, many mariners employ a less-expensive tablet or smart-phone. A program such as the Navionics Boating app, together with the mobile device’s built-in GPS, provides a stand-alone plotter. Navionics recently added the ability to display AIS targets, but the challenge remains of getting the AIS data into the device, since tablets and phones do not come with a built-in AIS receiver.
Connecting The Pieces
The multitude of interface standards can make it challenging to share data between components. Step one is to determine the physical connection and protocol that each device uses, and then figure out which translator or bridge device might be needed. Physical connection methods include RS-232, RS-422, CAN-bus, Ethernet, and WiFi. The language spoken (protocol) on each physical link also varies: common ones include NMEA-0183, NMEA-2000, NMEA OneNet, SignalK, SeaTalk and other proprietary protocols.
Navionics, with a valid annual subscription, now supports AIS display from receivers and transceivers connected to a mobile device (full details are available on the Navionics website). However, most phones and tablets have limited physical inputs; USB is possible with some but not all devices. How then, do you share data with your device? WiFi is popular – for example, many radar manufacturers now offer units that can cast the radar plot onto the tablet or phone’s screen. This is the approach taken by Navionics.
Legacy AIS receivers that lack WiFi can work with Navionics by using an appropriate bridge device to send AIS data over WiFi. The SR-161 has an RS-232 serial port, so we needed a serial-to-WiFi converter. The SR-161’s data format is NMEA-0183 sentences, which Navionics accepts as-is, so no protocol translator was needed.
Serial-to-WiFi bridges range widely in cost, depending on their features and whether they are made for the boating industry. The Digital Yacht WLN10, for example, is a basic bridge that costs about $270. It would likely have been suitable, but we found a less expensive solution.
We selected the Elfin EW10A, which is widely used to remotely administer computer devices, and is available on Amazon for about $27. Three steps are involved in getting the device to work: hooking it up, configuring the bridge, and configuring Navionics.
Installing the Device
The SR-161 shares information via a DE-9 serial port. The user manual states that the DE-9 male plug uses pin 2 for AIS data output, pin 3 for an optional GPS data input (echoed to pin 2), and pin 5 for signal ground. To make the data connection, we cut the end from a spare RS-232 cable to obtain a female DE-9 socket with a few inches of cable attached. We then used a multi-meter to determine which colour of wire corresponded to each pin.
|2||Brown||AIS Data Out|
|5||Yellow||Signal Ground (shared with the – wire from the power supply)|
The Elfin EW10A comes with a cable that ends in a 4-position screw terminal block: two pins are used for power, and two are for serial data. We connected the brown wire to the converter’s screw terminal labelled ‘Tx’ (indicating that data on this pin will be transmitted on the WiFi channel), and the yellow wire to the negative (–) screw terminal. The DE-9 socket is then plugged into the SR-161.
For the power connection, it is fine to feed both the AIS receiver and the serial converter from the same circuit, which should be protected by an appropriate fuse or circuit breaker. We measured current consumption of less than 0.2A and chose a 2A fuse. The EW10A accepts power in the range of 5 to 18 VDC. The power supply positive wire was attached to the converter’s screw terminal labelled ‘+’, and the negative supply wire was attached to the terminal labelled ‘–’. The SR-161 was similarly attached to the power supply, using it’s red (+) and black (–) wires.
The final connection is for a VHF antenna. For maximum range, it should be mounted outside and up high, away from other transmitting antennas (it is safe to mount it close to receive-only antennas, like GPS). A splitter can connect both voice VHF and AIS systems to a single antenna, but I advocate using a separate antenna for two reasons. First, splitters reduce signal strength (lowering range for both AIS and voice) and second, having two antennas provides you with a backup antenna in the event that the primary one is lost.
At this point, we powered up the system as a preliminary test. The SR-161’s red LED blinks when receiving AIS signals; the green LED flashes each time an AIS message is successfully decoded and sent to the serial port.
Configuring the Bridge
When the EW10A converter is powered up, it presents itself as a WiFi Access Point (AP), to which a laptop, tablet, or phone can connect. Using your device’s WiFi settings, search for and connect to the converter, which by default has the identifier EW10_xxxx. During the connection process, your device may prompt that internet connectivity is unavailable. This message is expected and may be ignored since the converter does not have any connection to the internet.
Once your device has connected to the EW10A, you can use the converter’s built-in web interface for configuration, or you can download a configuration program from the manufacturer. We found the web interface easy to use, and we have described that approach here.
To access the web interface, open a browser (e.g. Safari, Firefox, or Chrome), and type the converter’s IP address (default is 10.10.100.254) into the browser’s address bar and press return. This should open a prompt for a username and password (default is admin / admin), which leads to the pages for configuring the converter’s System, Serial, and Communication settings (examples are shown below).
These settings affect the WiFi interface and what functions are available. At minimum, the User Name and Password, and possibly the WiFi AP Key (Password), should be changed to keep others from re-configuring your converter. If the WiFi Channel chosen by the converter conflicts with something else on board (e.g. WiFi Radar), it can also be changed here.
These settings affect the serial interface with the AIS receiver. For an SR-161, change the Baud rate to 38400, 8 data bits, no parity bit, 1 stop bit, and Flow Control to Disable.
These settings affect how AIS data is presented to the connected laptop/phone/tablet. Navionics works with either TCP or UDP; we chose TCP Server. Note the Name and Local Port number, as they need to be entered in the Navionics configuration.
After adjusting the needed settings, go to the ‘Others’ page, and click on the ‘Restart’ button to reload all the new settings. If you have changed the AP name or IP address, or added a WiFi password, you will need to reconnect with the converter using the new credentials.
If you haven’t already done, so, connect your device running Navionics to the converter’s WiFi AP. Open Navionics, then click on ‘Menu’ → ‘Paired Devices’ → ‘Add Device’. In the resulting dialog, enter the Name, Host IP, Port Number, and connection Type (TCP or UDP) that you had previously set up. Click on ‘Save’ to complete the process.
That’s it! Your Navionics app should now display AIS targets as they come within range.