Networking Marine Instruments: – 07 | Integrating Analogue Sensors

Analogue Sensors on a NMEA 2000 Network: A Practical Guide for Boat Owners

Bringing Classic Sensors Into the Digital Age for Modern MFD Display

Modernising your vessel’s instrumentation by interfacing older analogue sensors with NMEA 2000 and NMEA 0183 networks is increasingly popular among boat owners. Not only does this approach preserve existing investments in proven hardware, but it also unlocks the functionality and convenience of displaying data on new-generation Multi-Function Displays (MFDs). This article explores the process, benefits, challenges, available devices, leading manufacturers, and practical examples, empowering you to make informed decisions for your refit project.

Your shiny new plotter and sailing instruments are ready for installation, but you still have those tarnished old analogue engine gauges; they don’t fit with your vision of a glass cockpit. Can we integrate the existing sensors and display them on the new MFD? Yes, we can!

The Analogue Challenge

Many older boats (and even some newer models) still rely on analogue sensors. These devices output electrical signals, typically voltage or resistance, that traditional gauges interpret. Common analogue sensors include:

• Engine sensors (RPM, oil pressure, coolant temperature)
• Battery monitors (voltage, current draw)
• Exhaust gas temperature sensors
• Speed, depth, and water temperature transducers
• Tank monitoring (fuel, water, grey water, black water)
• Rudder feedback unit (rudder position sensor for autopilots)

These sensors are reliable and time-tested, but they speak a different “language” from digital NMEA 2000 devices. To bridge that gap, you’ll need an analogue-to-NMEA 2000 converter.

Examples of Analogue Sensor Integration

There are numerous sensor types commonly integrated with NMEA 2000 or 0183 networks via analogue-to-digital conversion. Some of the most popular applications include:

Depth, Speed, and Temperature Sensors

Exhaust Gas Temperature (EGT) Sensors

Analogue Engine Instruments

Alarms and Switch Monitoring

Switches for bilge pumps, navigation lights, or security alarms can be monitored using digital input modules. Yacht Devices’ Switch Input Module, for example, can detect the state of up to eight inputs and broadcast their status over NMEA 2000. This integration allows for MFD-based alerting and control.

Rudder Reference Units

Analogue rudder angle sensors, typically potentiometer-based, can be integrated using a rudder reference interface module, translating angular position into digital data. Maretron’s Rudder Angle Sensor is a popular option for such conversions.

Tank Level Sensors

Switches and Outputs

Output modules can be used to control devices—such as activating lights or pumps—via digital commands from an MFD or networked keypad. This allows for remote and automated operation, integrating traditional vessel systems into a modern digital ecosystem.

How to Integrate Analogue Sensors

1. Choose the Right Converter

The key to bridging the analogue-digital divide is the use of signal converters or gateways. These devices read the output from an analogue sensor and translate it into standard NMEA 2000 or NMEA 0183 messages.

• Analogue-to-NMEA 2000 Gateways: These devices convert sensor signals to NMEA 2000 PGNs (Parameter Group Numbers) for modern network compatibility.
• Analogue-to-NMEA 0183 Converters: For legacy networks, these devices output NMEA 0183 sentences from analogue sources.
• Multiplexers: Combine multiple analogue and digital sources and output in NMEA 0183 or NMEA 2000 formats.
• Custom Signal Conditioners: For non-standard sensors, signal conditioners can normalise voltages or resistances for converter compatibility.
• Input/Output Modules: Some modules can handle switch states, alarms, and relay activation, integrating this data into digital networks.

Who makes these things?

Several manufacturers offer analogue-to-NMEA 2000 conversion devices. Popular brands include:

• Actisense: Well known for their EMU-1 for engine gauges
• Yacht Devices: Offers a vast range of NMEA 2000 and NMEA 0183 input/output modules, tank adapters, battery monitors, and sensor gateways.
• Maretron: Has a great range of adapters and a very well-documented site.
• Vetus, Airmar, and others for depth/speed/temperature transducers
• Garmin, Raymarine, Simrad, Furuno: Major electronics brands often supply proprietary analogue-to-digital interfaces or recommend compatible third-party solutions.
• Victron: has a huge range of, mainly, power products, many of which can be integrated into your network. They have an excellent guide here.

When selecting a converter, make sure it is compatible with the sensor type and electrical signal range of your existing equipment.

2. Identify Sensor Types and Signals

Before installation, determine what type of signal each sensor produces. For example:

• A temperature sensor might be a resistive thermistor.
• A tachometer might use a pulsed signal from an alternator or magnetic pickup.
• A battery monitor will use voltage and/or current measurement.

Consult sensor datasheets or use a multimeter to verify signal types.

3. Install the Converter

Installation usually involves:

• Connecting the analogue signal wires to the input terminals on the converter.
• Configuring the converter (via PC software or DIP switches) to interpret the input correctly.
• Connecting the converter to your NMEA 2000 backbone using a standard N2K T-connector.

Ensure all electrical connections are watertight and follow marine-grade standards.

4. Configure and Calibrate

Most converters allow customisation of the data interpretation. This might involve:

• Calibrating resistance-to-temperature curves
• Defining voltage ranges
• Setting engine parameters like cylinder count or gauge scaling

Proper setup ensures accurate and reliable data output to your chartplotter, MFD, or other display device.

Pros and Cons of Integrating Analogue Sensors

Pros

• Unified Data Display: View all key boat information — engine RPM, battery status, depth, speed — on one or more displays.
• Data Logging: Capture and analyse performance or maintenance data over time.
• Alerts and Alarms: Set up custom alarms for temperature spikes, low battery voltage, or water depth warnings.
• Future-Proofing: Gradually upgrade your boat’s systems without having to replace everything at once.
• Cost-effective: Retain functional analogue sensors and save on the expense of a full system replacement.
• Proven Reliability: Classic analogue sensors have stood the test of time and are well-suited to the harsh marine environment.
• Reduce Waste: Reusing existing, functional components reduces electronic waste.

Cons

• Single point of failure: If the network goes down you have lost visibility of your sensors.
• Need to scroll: the screen of the MFD to display vital information
• Cost: There will be some cost involved in the interface devices, and this needs to be weighed against the cost of replacement digital sensors.
• Network complexity: inevitably, the network becomes larger, but this shouldn’t be a showstopper.
• Calibration complexity: Analogue to digital conversion requires careful setup and calibration for accurate readings. It may always be as easy as the manufacturers of the interfaces claim.
• Certification and safety: Integrating some instruments this way may not meet marine certification standards, which can potentially affect insurance or compliance.

Final Thoughts

Integrating analogue sensors into your NMEA 2000 network is a smart and cost-effective way to modernise your boat. It extends the life of your current equipment while giving you access to the benefits of digital data sharing and centralised monitoring. Whether you’re monitoring tank levels, engine health, or navigation parameters, this approach maximises your onboard information while making the most of your existing investments. With a bit of planning and the right hardware, you’ll be navigating with smarter systems — and greater confidence — in no time.

If any specific sensor types, brands, or integration scenarios are not covered here, or if you have unique requirements, please let me know so I can address them directly.

Have I missed any important aspect of your project? Your feedback and questions are welcome to make this guide even more comprehensive. Please leave a comment.

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