Ultrasonic tank sensor with SensESP

Fig .: Ultrasonic level sensor



Fred has another implementation of an ultrasonic tank sensor with him SensESP  and a Wemos D1 mini. The Ultrasonic sensor DS1603L detects liquid levels in a tank and provides the corresponding measured values via SensESP via WiFi SignalK. SensESP is a software framework for the Arduino IDE with which different sensors can be easily integrated into SignalK. The special thing about SensESP is that sensors can be docked in SignalK without a network configuration. A SignalK server is automatically recognized by SensESP and the network configuration for data transmission via WiFi is carried out independently. The level can be visualized in SignalK.

Due to the properties of the sensor, there is no need to drill a hole in the tank, which is why this sensor can be used as a retrofit solution for existing tanks without a level indicator. Thanks to the WLAN connection, no further data cables need to be laid; a 12V supply near the tank to which the microcontroller can be connected is sufficient. The Wemos D1 mini pro module is a microcontroller based on the ESP 8266 with built-in WLAN module. The ultrasonic sensor is connected to the microcontroller. The ultrasonic sensor is glued to the outside of the tank bottom. The liquid level in the tank can then be recorded.

Caution: The sensor must be attached to the bottom of the tank, so it must "ping" from bottom to top in order to record the liquid level. "Pinging" from top to bottom does not work.

The software for the level sensor can be found here: https://github.com/frewie/UltrasonicTankSensor

We have a similar project under DIY ultrasonic level measurement to find. However, it uses its own software that can transmit NMEA0183 data sets via WiFi.

Fig .: Waterproof housing for the level sensor

Integrate WiFi battery monitor in SignalK

First of all, a few important notes that you should definitely pay attention to.

Fig: WiFi battery monitor

The WiFi battery monitor can be integrated into SignalK. The measurement data can then be displayed in the instrument panel. A small detour via MQTT is necessary for integration in SignalK. Since the WiFi battery monitor can also communicate with the Tasmota software via MQTT as standard, we use this interface in conjunction with the SignalK plug-in signal-mqtt-gw by Teppo Kurki. Basically, we don't need an MQTT server on the Raspi if we want to use the SignalK plugin. If an MQTT server is running on the Raspi, the port addresses must be changed to avoid conflicts. The SignalK plug-in behaves like an MQTT server and can interpret the telegrams sent, but without error handling and special transaction protection. The following shows how the configuration must be carried out.

WiFi battery monitor configuration

Under Configure MQTT the following settings are made:

  • Host: IP of the Raspi is running on the SignalK
  • Port: 1883 (change if an MQTT server should run on the Rapi)
  • Client: PZEM-017 (name of the device that is displayed as source in MQTT)
  • Topic: service
  • Full Topic: battmonitor / service

Username and password remain unchanged and are not used.

Fig: Configure MQTT

Then is still under Configure Other to check whether MQTT is activated.

Fig: Configure Other

Under Configure logging the update rate is set with which the telegrams are to be sent. There is also the parameter Telemetry Period. The value is given in seconds. 10 can be used as the smallest value. Data transfers faster than 10s are not possible. The measurement data are then displayed in SignalK with this update rate.

Fig: Configure logging

As a last step, we have to add two special rules to the Tasmota firmware that processes the data telegrams so that they can be used by the SignalK plug-in  signal-mqtt-gw can be processed. Rules are Tasmota firmware extensions with which the behavior of Tasmota can be influenced. If you want to know more about how it works, you can do this here read in detail. The SignalK plug-in for MQTT always expects individual data pairs per telegram with an identifier and a measured value. The identifier corresponds to the data path in SignalK. The data paths should not be chosen arbitrarily and should adhere to the specifications for data paths. Details can be found in the SignalK documentation in the appendix under appendix A and B. Both rules split the original MQTT telegram into 8 individual MQTT partial telegrams as can also be seen in the logging.

18:07:37 MQT: battmonitor / service / SENSOR = {"Time": "2021-04-18T18: 07: 37", "ENERGY": {"TotalStartTime": "2021-04-09T17: 21:15" , "Total": 0.122, "Yesterday": 0.011, "Today": 0.111, "Period": 0, "Power": 6, "Voltage": 13.03, "Current": 0.470}, "DS18B20-1": {"Id": "3C01D6075272", "Temperature": 23.0}, "DS18B20-2": {"Id": "3C01D607E5E3", "Temperature": 23.3}, "TempUnit": "C"}

Rule1 takes care of the forwarding of the temperature values

ON DS18B20#Temperature DO Var1 %value% ENDON
ON DS18B20#Temperature DO Add1 273.15 ENDON
ON DS18B20-1#Temperature DO Var2 %value% ENDON
ON DS18B20-1#Temperature DO Add2 273.15 ENDON
ON DS18B20-2#Temperature DO Var3 %value% ENDON
ON DS18B20-2#Temperature DO Add3 273.15 ENDON
ON DS18B20-3#Temperature DO Var4 %value% ENDON
ON DS18B20-3#Temperature DO Add4 273.15 ENDON
ON tele-DS18B20 DO publish vessels / self / environment / inside / DS18B20_1 / temperature %Var1% ENDON
ON tele-DS18B20-1 DO publish vessels / self / environment / inside / DS18B20_1 / temperature %Var2% ENDON
ON tele-DS18B20-2 DO publish vessels / self / environment / inside / DS18B20_2 / temperature %Var3% ENDON
ON tele-DS18B20-3 DO publish vessels / self / environment / inside / DS18B20_3 / temperature %Var4% ENDON

The temperature values are read in and converted into Kelvin, since SignalK always expects measured values in SI units.

Rule2 processes the electrical measured values.
ON ENERGY#Power DO Var5 %value% ENDON
ON ENERGY#Voltage DO Var6 %value% ENDON
ON ENERGY#Current DO Var7 %value% ENDON
ON ENERGY#Total DO Var8 %value% ENDON
ON ENERGY#Yesterday DO Var9 %value% ENDON
ON ENERGY#Today DO Var10 %value% ENDON
ON tele-ENERGY DO publish vessels / self / electrical / batteries / service / power %Var5% ENDON
ON tele-ENERGY DO publish vessels / self / electrical / batteries / service / voltage %Var6% ENDON
ON tele-ENERGY DO publish vessels / self / electrical / batteries / service / current %Var7% ENDON
ON tele-ENERGY DO publish vessels / self / electrical / batteries / service / energytotal %Var8% ENDON
ON tele-ENERGY DO publish vessels / self / electrical / batteries / service / energyyesterday %Var9% ENDON
ON tele-ENERGY DO publish vessels / self / electrical / batteries / service / energytoday %Var10% ENDON
The two rules are entered individually as a complete text string in the console and confirmed with Enter. Then we still have to set the rules with the commands Rule1 ON  and Rule2 ON activate. The breakdown and the individual telegrams should then be visible in the console.
Fig: Console with individual telegrams for the measured values
Here are some more important commands for rules:
  • RuleX 0 - deactivates a rule
  • RuleX " - deletes a rule
  • RuleX ON - activates a rule

Configuration in SignalK

On the Raspberry Pi you should first check whether an MQTT server like mosquitto running. The easiest way to do this is in a console with the command Top do. It shows a list of all running processes on the Raspi. If the MQTT server is running without being used, then you should use the command sudo apt-get remove mosquitto deinstall. If it is required, a port other than 1883 must be used in the configuration.

In SignalK the plugin signal-mqtt-gw under Appstore -> Available Installed. Under Server -> Plugin Config the following settings are then made.

Fig: Plugin Config in SignalK

If everything is configured correctly, SignalK must be restarted. Then the data is in the Data browser to see.

Fig: SignalK Data Browser

Depending on the number of connected 1Wire temperature sensors (DS18B20), temperature values are then displayed. If the InfluxDB database and the Grafana database front end are also installed, extensive graphic data evaluations can be carried out.

Fig: Measurement data in the SignalK instrument panel

Fig: Measurement data visualized with Grafana


WiFi battery monitor

First of all, a few important notes that you should definitely pay attention to.

While searching the Internet for a battery monitor for DC voltages, I came across the PZME-017. The Peacefair company is known for various inexpensive battery monitors with LCD displays such as the PZEM-015.

Fig: PZEM-017 (100A version, with shunt and USB-RS485 adapter)

Fig: PZEM-015 (300A version as a pure display variant)

The PZEM-017 has the following features:

  • Voltage measurement 0… 300V DC
  • Current measurement: 10A, 50A, 100A, 200A, 300A (from 50A via external shunt)
  • Display of the current power in watts
  • Energy display in kWh for the current day, previous day and total consumption display
  • Modbus RTU-Interface (RS485, 9600Bd, 8N2, binary data transmission)
  • Supported Modbus commands:
    • 0x03 Read memory register
    • 0x04 Read input register
    • 0x06 Write single register
    • 0x41 calibration
    • 0x42 Reset energy measurement
  • 7 devices can be used on the Modbus via adjustable ID 1… 7, ID 0 broadcast
  • USB-RS485 adapter (CH341)

In contrast to the PZEM-015, the PZEM-017 has no display and transmits the measurement data via the Modbus. The Modbus protocol is open and there are some implementations with an arduino. The website is an example here Solarduino called. There, however, a TTL-RS485 adapter is used to connect to the Arduino. In the area of home automation there are implementations with a Wemos D1 mini (ESP8266) with Tasmota firmware and a data connection via WiFi. However, it cannot be used well as a battery monitor on a boat, as you still need an external power supply of 5V for the Wemos D1 mini.

The Tasmota firmware already has all the important interfaces that you need to be able to build a boat battery monitor:

  • Supports all PZEM modules with Modbus interface via TTL signals with unsoldered RS485 chip (U5)
  • Supports temperature 1-wire modules such as the DS18B20
  • Web configuration
  • Display of the measurement data on the website

After some reengineering of the electronics I was able to modify the circuit so that it does not need an additional 5V supply and only needs a few components such as:

  • Wemos D1 mini with Tasmota firmware
  • 1k resistor
  • 4K7 resistor
  • 7 connection cables
  • DS18B20 temperature sensor

and a stand-alone boat battery monitor has been created that can:

  • Input voltage 10… 38V
  • Voltage measurement accuracy: 0.01V
  • Current measurement: 10A, 50A, 100A, 200A, 300A (from 50A via external shunt)
  • Current measurement accuracy: 50mA
  • Display of the current power in watts
  • Energy display in kWh for the current day, previous day and total consumption display (not power off resistant when completely switched off, details look here)
  • Resettable energy meters
  • Configuration and display of the measurement data via the website
  • Temperature measurement: 1… 3 DS18B20 for battery, charger and inverter (operated in parallel on the 1-Wire bus)
  • Own consumption: 16mA (without WiFi activity), 60mA (with WiFi data traffic, if connected)
  • Reduced power consumption of only 1.0mA when the Wemos D1 mini is switched off (look here)

Circuit modification

 Unsolder IC U5 (MAX485)

The IC U5 is not required because we do not use the Modbus and connect the serial TTL data signals (3.3V) directly to the Wemos D1 mini. The easiest way to unsolder it is with a hot air desoldering station. If you don't have this, you can heat up each pin of the IC individually with the soldering iron and carefully bend it up with a needle. But you have to make sure that the pin is not heated for too long, otherwise the conductor track underneath will become detached from the circuit board. This must be avoided at all costs, as we still need the pads to solder the cables. It is also important to note how U5 was soldered in, as the cables are soldered according to the pin numbers according to Table 1.

Fig: Pin numbers

Fig: Position of U5 (unmodified board)

Solder in 1k resistor

The 1k resistor has to be soldered parallel to R15. R15 is the series resistor for controlling the optocoupler U2 (CT817C Receiving side). With the resistor soldered in parallel, R15 is reduced to 320 Ohm, so that the LED of the optocoupler can be controlled from the Wemos D1 mini with a 3.3V TTL signal.

Fig: 1k resistor

Solder the 4K7 resistor and bridge

The 4k7 resistor serves as the Pull-up resistor for the 1Wire bus. It is soldered to the pads of the missing resistor R19. In addition, a small bridge from R19 to R17 is soldered as can be seen in the picture. This connects the resistor to 3.3V.

Fig: 4k7 resistor with bridge

Solder the 3.3V supply voltage to the Modbus output circuit

Since the Modbus output circuit is operated electrically isolated from the measuring circuit via the optocoupler, an external supply voltage of 5V is required in the original circuit. This is fed in via the Modbus connections. In our case, however, we do not need electrical insulation, as we transmit the data via WiFi and operate the rest of the circuit with the same 3.3V supply voltage as the measuring circuit. For the feed we need a black cable from Z2 to U1 pin 3 and a red cable from plus E1 to C7.

The optocouplers actually no longer make sense. We still need them because the signals from the microcontroller U3 are inverted and we cannot use them directly.

Fig: Supply lines

Solder in the Wemos D1 mini

The connections of the Wemos D1 mini are soldered to the free pads of U5 as follows:

Cable color From Wemos D1 mini To meaning
red 3V3 U5 pin 8 3.3V supply
black G U5 pin 5 Dimensions
green TX (GPIO 1) U5 pin 1 Receive Modbus
green RX (GPIO 3) U5 pin 4 Send Mosbus
yellow D1 (GPIO 5) R19 lower pad 1-Wire data signal

Tab. 1: Cable assignments

Fig: Pin assignment Wemos D1 mini

Fig: Cable on the Wemos D1 mini

Fig: Assignment of the cables to U5

Flash Tasmota firmware

Before the Tsmota firmware is flashed, the following must be observed:

Note! In our modified circuit, the Wemos D1 mini is not operated with the 5V supply, but with 3.3V directly from the measuring circuit. If the Wemos D1 mini is supplied with 5V via the USB connection, the battery monitor must be disconnected from the 12V supply and from the shunt. Otherwise there will be a double feed and the Wemos D1 mini or the PC could be damaged. So all 4 cables must always be disconnected from the measurement connections when working with the USB cable.

The current version of the Tasmota firmware can be downloaded here: http://ota.tasmota.com/tasmota/release/ The firmware is available in different language versions. The tasmota.bin file would be a good choice for English-language firmware. If you want to know more about Tasmota, you can visit this website: https://www.tasmota.info There you will find detailed information about supported hardware and flashing.

The easiest way to flash the firmware is with the software Tasmotizer which are available for different operating systems. It works best with the Windows variant.

When flashing via the USB cable, we must not forget to check the box next to “Self-resetting device”. The Wemos D1 mini is automatically switched to programming mode and automatically reset after flashing.

Fig: Tasmotizer settings

Tasmota configuration

The Tasmota firmware is universal and supports a variety of devices. With the configuration, the firmware is adapted to the specific hardware. After flashing, the Wemos D1 mini starts with its own access point, which can be reached under the SSID tasmota_xxxxxx. A password for logging into the WiFi network is not required. The start page can be opened with a web browser under the IP address The respective settings are made under Configuration as shown in the following images.

Fig: Configure WiFi: Enter SSID, password and host name

Fig: Configure tamplate: Select Based on Generic (18), assign the name PZEM-017 and assign GPIOs

Fig: Configure Module: Select module type PZEM-017 (0)

Fig: Configure Other: Assign Device Name Battery Monitor

This completes the configuration and we can see the measured values on the start page of the battery monitor.

Fig: Battery monitor home page

Safe installation in the housing

The Wemos D1 mini can be accommodated in the same housing as the battery monitor. I packed the Wemos D1 mini in a small zip bag. This means that no short circuits can occur with the rest of the circuit and everything is securely packaged. You could of course do the isolation with tape. With the zip bag, however, it is more convenient because you can remove the Wemos Di mini for later software changes.

Fig: Isolation of the Wemos D1 mini in a zip bag

Fig: Closed housing

Connection of the temperature sensor

The DS18B20 temperature sensor can be connected to the connections of the RS485 bus as follows:

Connection RS485 port New function DS18B20
5V 3.3V not used
B. 3.3V red
A. 1-Wire yellow
GND GND black

Tab: Terminal assignment temperature sensor DS18B20

Fig: Test circuit with shunt, load resistor and temperature sensor equivalent to the circuit diagram on the back of the battery monitor

Fig: circuit

Further information

Separate micro USB port

The separate micro USB port on the side of the battery monitor is used for power supply if the battery voltage should drop below 7V. A separate USB cable can then be used to supply an external power supply. As noted in the documentation, this is very dangerous if the battery voltage is greater than 7V. Then the feeding devices can be destroyed via the feed from a PC or a power bank, because the higher voltage is then applied to the feeding devices with the maximum current of the battery. It is therefore not advisable to use this micro USB port. It's just too dangerous.

1-wire port

Up to 3 temperature sensors can be connected in parallel to the 1-Wire port. The sensors can be used, for example, to measure the temperature of the battery, the charger, the solar regulator or the inverter. Any other application would also be conceivable. The Tasmota firmware will automatically detect the additional temperature sensors and display the temperature values below the values from the battery monitor. The assignment of the sensors to the IDs must be found out by testing the sensors.

Power supply

If the battery voltage is less than 10V, the WemosD1 mini will no longer function properly. The Wemos D1 mini gets stuck, especially when switching on with voltages below 10V. Overvoltages above 40V are possible, but should not be present for too long as the power supply heats up significantly.

Current measurement

The current measurement with the PZEM-017 shows an offset of 0.05A for a 100A shunt and thus falsifies the counting of the amount of energy. Only positive measuring currents can be processed. Negative currents through chargers are permitted, but are not taken into account in the energy measurement.

Subsequent change of the shunt value

When the PZEM-017 is delivered, the correct shunt value is entered in the firmware. If you want to use other shunt values, you can reprogram this using the Modbus commands before converting the circuit. It should be noted, however, that the shunts must be designed for 75mV and only the shunt values for currents 50A, 100A 200A and 300A are supported. Switching to other shunt values is done exclusively by software. Internally, only another conversion of the voltage measured at the shunt is carried out. The measurement accuracy is therefore dependent on the shunt used. The measured values for shunts are correspondingly more accurate for smaller currents and less accurate for higher currents.

Setting the shunt value:

01 06 00 03 00 00 79 CA 100A
01 06 00 03 00 01 B8 0A 50A
01 06 00 03 00 02 F8 0B 200A
01 06 00 03 00 03 39 CB 300A
01 06 00 03 00 04 78 09 10A (internal shunt)

01 - ID
06 - write parameters
00 03 - register no.
00 00 - Shunt value (00 00 - 100A)
79 CA checksum


01 06 00 03 00 00 79 CA 100A
01 06 00 03 00 01 B8 0A 50A
01 06 00 03 00 02 F8 0B 200A
01 06 00 03 00 03 39 CB 300A
01 06 00 03 00 04 78 09 10A (internal shunt)

01 - ID
06 - write parameters
00 03 - register no.
00 00 - Shunt value (00 00 - 100A)
79 CA checksum

Energy measurement

The energy measurement is a measurement of voltage and current over time. The product of voltage, current and time interval is formed and the following values are added up. A Peukert factor is not taken into account in the measurement. It is a pure energy measurement.


Measurements on the PZEM-017 with a 100A shunt showed that the battery monitor has precise measurement functions. Only a voltage offset of + 0.01V and a current offset of + 0.05A could be identified as errors. This is completely sufficient for typical applications. In the case of versions with a 200A and 300A shunt, larger errors must be expected as the measurement resolution decreases. A calibration directly on the device via potentiometers cannot be carried out and must be carried out externally with special software from Peacefair. For calibration you need a stable and precise 30V supply and a very accurate 10A power source. Tests with a self-performed recalibration did not produce any better results than the factory calibration.

Storage of measured values

All measured values are lost after the supply voltage is completely switched off and the values of the energy measurement are set to zero. If you want to avoid this, you have to continue to supply the measuring circuit with battery voltage. The pure power consumption of the measuring circuit is only 1mA at 12V. So if you want to continue to receive the energy values, you can only switch off the Wemos Di mini and keep the measuring circuit supplied. This reduces the power consumption from 70mA to just 1mA. For further details see also in the chapter Reduce power consumption.

Reset the counter values

The counter values cannot be reset via a button on the main page of the battery monitor. A little detour via the console is necessary for this. The command EnergyReset 0 entered in the console and confirmed with Enter.

Display decimal places for voltage values

By default, the Tasmota firmware only shows the voltage without decimal places. Up to two decimal places can be displayed if you enter the following command in the console:

VoltRes 2

Set the correct system time

The Wemos D1 mini gets the current time from the Internet via an NTP server. The correct time for Germany can be found on the console with Timezone 99 can be set. Any other time zone can be with Time zone -13 ... + 13 can be set hourly as an offset. In the event that the battery monitor is not connected to the Internet but would like to obtain a current time from an NTP server in its own network, it is possible to redefine several NTP servers. The following commands are required one after the other:

NtpServer 0 (deletes the NTP settings, pay attention to spaces after NtpServer!)

NtpServer1 ptbtime1.ptb.de (sets NTP server 1)

NtpServer2 ptbtime3.ptb.de (sets NTP server 2)

NtpServer2 ptbtime3.ptb.de (sets NTP server 3)

More information about all Tasmota commands can be found here: https://tasmota.github.io/docs/Commands/

Embed measured values in external websites

The measured values of the battery monitor can also be output as formatted data. To do this, you connect to the battery monitor via HTTP

and then receives the following answer

{t} {s} Voltage {m} 0.00 V {e} {s} Current {m} 0,000 A {e} {s} Power {m} 0 W {e} {s} Energy Today {m} 0,000 kWh { e} {s} Energy Yesterday {m} 0,000 kWh {e} {s} Energy Total {m} 0,000 kWh {e

If you want to access this data on third-party websites, you have to CORS (Cross Origin Resource Sharing) in the Tasmota firmware. This is done with the following command via the console:


Any website can then call up the data externally. If you want to use the access a little more restricted, you can also use the following command:

CORS http://my.webside.com

A small example can be found here: Demo_PZEM-017.zip

Fig: Integration in your own HTML pages

Integrate measured values in SignalK

The measured values can also be integrated into SignalK and can then be displayed via the instrument panel. How the configuration works in detail is described here:


Fig: Measurement data in the instrument panel

Reduce power consumption

The power consumption of the battery monitor can be reduced quite significantly to 1.0 mA at 12 V if the Wemos D1 mini can be switched off using a small switch (red cable 3.3V). The original measuring circuit then continues to run in the switched-off state and counts the power consumption. Only data transmission and display of the measurement data is then no longer possible. After switching on the supply voltage, all data are transmitted again and displayed correctly. This is very useful when you are not on the boat, so as not to discharge the battery.


Fig: Installation position for the on / off switch

Measurement of the consumption data of the AC shore connection

If you also want to measure the consumption data of the AC shore connection, you can do this with the Sonoff Pow Power Monitoring Switch with the Tasmopta firmware do. The shore connection can also be switched on and off via the module. The newer variant is the Sonoff Pow R2. It has a larger range of functions and can display more measured values and react to limit values. An ESP8266 is already built into these two devices and is only operated with the Tasmota firmware. A modification of the electronic circuit is not necessary as with the battery monitor. The Sonoff Pow R2 is therefore a good addition to the battery monitor.

Fig: Sonoff Pow (R2)

Low budged energy monitor

Stefan Kaufmann has on his website https://obenschlaefer.com/ presented an inexpensive energy monitor that is also interesting for boat enthusiasts. He originally built the energy monitor for his camper in order to be able to monitor the energy supply. The system is based on components from Victron on. The centerpiece is a Raspi with the free Venus OS firmware from Victron, which is also included in commercial hardware runs, but in this case on an inexpensive Raspi3B. The Raspi is then the control and visualization center for the energy monitor. Operation is web-based using a mobile phone, tablet or PC. In his building instructions he uses a 7 ″ Raspi display on the back of which the Raspi is docked. The Victron components are connected to the Raspi via Bluetoth and use it to exchange data.

Basically, the following things can be done with it:

  • Display of the energy flows between generators (generator, solar cell, charger), storage (lead-acid battery, LiFePo4, etc.) and consumers
  • Remote diagnosis via the Internet
  • Reporting system in the event of device malfunctions
  • Supported devices from Victron:
    • Victron battery computer BMV712
    • Victron MPPT solar charge controller of the Smart-Solar series
    • Victron inverters of the Phoenix series
    • Victron 230V charger of the Phoenix series

Stefan has described his project in great detail on his homepage. In multi-part videos, he describes exactly how the system is set up and what needs to be taken into account. There should hardly be any questions left unanswered.

Venus OS by Victron

Built-in components


Integrate Ruuvi Sensor Tag in SignalK

Video: https://youtu.be/NCJYmDuf2Jg

The Ruuvi sensor day is a small, smart sensor device. This allows the following data to be recorded:

  • temperature
  • Humidity
  • Air pressure
  • 3-axis acceleration sensor
  • waterproof case
  • Data storage in mobile phone app
  • Android and iPhone app available

The data is sent to a data terminal at defined time intervals to save energy via Bluetooth Low Energy. This can be a cell phone, for example, where you can view the data. But there is also a gateway with which the data can also be transferred to other systems such as:

  • SignalK
  • Grafana
  • Io tool
  • Steamr
  • TTN network
  • Node Red
  • and many more services

The Ruuvi Sensor Tag has a large 1000mAh rechargeable battery in the form of a CR2477 battery. This means that data can be recorded for up to 3 years depending on the recording rate, with the data being saved with the current firmware 2.5.9 delivered externally and not in the Ruuvi Sensor Tag. Either the cell phone or a gateway is used to transfer the data to other systems. From the Beta firmware 3.29.3 then the internal storage of the data also works. The case has 2 buttons and two LEDs and measures 52mm in diameter, is 12.5mm thick and weighs 25g. A exact specification is here to find. The Ruuvi Sensor Tag was created as part of a coupon funding campaign and pursues an open strategy of open hardware and open source. Much of the Construction documents are freely available. Various Firmware versions can be downloaded for different applications.

The integration of the sensor tag in SignalK takes place via the signal-ruuvitag-plugin. The corresponding sensor tag can be selected via the plug-in based on its ID and easily assigned to a sensor scheme in SignalK. The received data can then be displayed live in the instrument panel. Long-term evaluations can be carried out with Grafana via the InfluxDB in SignalK.

The Finnish company of the same name Ruuvi is offering the Sensor Tag for 35 euros in over 100 countries.

Long-term evaluation with Grafana

Front Ruuvi Sensor Tag

Extension connections of the Ruuvi Sensor Tag on the back

Visualization with Grafana



Data display in mobile phone app

Related Links


GaladrielMap navigation software

First of all, a few important notes that you should definitely pay attention to.

GaladrielMap is a web-based navigation software from Vladimir Kalachikhin. The name of the software is named after his boat. The software is based on a large number of PHP scripts that generate websites and are published via a web server. The websites can be displayed on any end device such as mobile phone, tablet and laptop. Only a web browser is required on the end device. The output of the navigation software can be displayed under all common operating systems. GaladrielMap has the following features:

  • Display of nautical charts online and offline via cache (OpenSeaMap, OpenTopoMap)
  • Display of your own position via GPS data provided by gpsd
  • Creation of your own routes
  • Creation of driven routes or POIs as gpx, kml and csv
  • Display of AIS information
  • Share your AIS position with others
  • Display of the weather forecast via Thomas Krüger Weather Service
  • Dashboard for displaying navigation data as numerical values

There is one for GaladrielMap virtual machine for Virtual Box to test the software functionality. There is also a executable image for a RaspberryPi with which a finished server with all necessary components can be set up. The image only needs to be saved on a 32GB SD card and then plugged into the RaspberryPi. In addition to the RaspberryPi, there is also the option of Navigation software on a modified WLAN router to run with OpenWRT.

A description and precise installation instructions can be found on Github: https://vladimirkalachikhin.github.io/Galadriel-map/

Route creation

Generate offline nautical charts

Display of AIS information

Share your own location with others

Display of weather information

Saving tracks

Car WiFi router MT7620A 300Mbps and 3G / 4G / LTE Internet gateway with OpenWRT firmware and integrated GaladrielMap

Car WiFi router front view

Car WLAN router in lockable installation frame


Weather forecast with AZ-Touch

The AZ touch Mod is a small 2.4 ″ touch color display with 320 x 240 pixels. On the base board can be used as a control unit ESP32C or a Wemos D1 mini be attached. A small breadboard allows you to set up your own circuits to expand the display.

The AZ-Touch has the following features:

  • Wall housing 120mm x 80mm x 35mm (W x H x D)
  • Resistive touchscreen 2.4 inch (6.14 cm) color TFT with 320 x 240 pixels (ILI9341)
  • For D1mini or ESP32 Dev-Kit C V2 / 4
  • built-in piezo buzzer
  • Integrated 5V voltage regulator (input voltage 9 - 35V DC)
  • Power consumption approx. 0.7W

On the website of Zihatec.de you can find the full description and the Circuit diagram about the AZ-Touch as well as some software examples.

The weather forecast is available in two versions. Once for the ESP32C and once for the Wemos D1 mini. The weather data is downloaded from the Internet by logging the display into an Internet-enabled WLAN.

Here is a little video about it: https://youtu.be/BkN-VGN96Cg


First of all, a few important notes that you should definitely pay attention to.

SensESP is a library that facilitates the integration of ESP8266 and ESP32 based sensors and actuators in a signaK network. The framework is based on PlatformIO and is mostly written in C++. Basically, recurring and important functions are mapped by the framework, so that programming and connecting your own sensors to SignalK is quite easy. Currently there are several well-documented examples of different sensors such as:

  • Tank sensor (10 ... 180 Ohm)
  • Temperature sensors (DS18B20, SHT31)
  • Temperature sensors with a thermopile sensor for higher temperatures up to 500 ° C
  • Voltage measurement 0… .15V
  • BME280 environmental sensor (temperature, air pressure, humidity)
  • Frequency counter (e.g. for wind speed, motor speed, shaft speed)
  • Heading sensor (9DOF)
  • GPS coordinates with speed and direction
  • Battery monitoring with INA219
  • Brightness sensor
  • Speed sensor
  • Relay control as output when measured values exceed limit values

The repository also contains a universal board for an ESP8266 to which various sensors can be connected.

custom-built ESP32 development board in a waterproof enclosure

Here is a software example for a flow sensor:

#include "sensesp_app.h"
#include "wiring_helpers.h"

ReactESP app ([] () {
SetupSerialDebug (115200);

// create a new application for flow meter
sensesp_app = new SensESPApp ();

// setup the fuel flow meter on two pins
// ESP8266 pins are specified as DX
// ESP32 pins are specified as just the X in GPIOX
#ifdef ESP8266
uint8_t pinA = D5;
uint8_t pinB = D6;
1TP3 Telif defined (ESP32)
uint8_t pinA = 4;
uint8_t pinB = 5;

// setup flow meter
setup_fuel_flow_meter (pinA, pinB);

// start application
sensesp_app-> enable ();

Example circuit diagram (Fritzing)

Realization on breadboard

Realization as a circuit board (Gerber Files)

Here is a more professional one Board with ESP32 and breadboard for your own circuits

Order shop for the board: https://hatlabs.fi/?v=3a52f3c22ed6

Additional information

Examples: https://github.com/SignalK/SensESP/tree/master/examples

Sources: https://github.com/SignalK/SensESP

Thread (german sailing-forum) https://www.segeln-forum.de/board194-boot-technik/board35-elektrik-und-elektronik/board195-open-boat-projects-org/78521-sensesp-a-signal-k-sensor-development-library-for-esp8266-and-esp32/

Background stories:

Multifunction display OBP 60

First of all, a few important notes that you should definitely pay attention to.

Display in action


open boat projects LIVE:
Video presentation in German on the OBP 60 multifunctional display (45min presentation, 30min discussion)

After we have dealt with the M5Stack as a multifunction display in 2019 and could show and were able to show some applications at Boot 2020, we are taking a new approach to a new multifunction display here. The M5Stack was not bad, but was subject to certain limitations for which some marine applications were not possible.

The disadvantages of the M5Stack include:

  • Display that is too small and not suitable for sunlight
  • Only 3 control buttons
  • Not waterproof
  • Too low battery power for standalone applications

However, some useful applications could be implemented:

The M5Stack is very flexible to use and well documented, but could not convince in the large number of marine applications. Following the widely used and popular ST60 series of instruments from Raymarine, a new attempt was made to build a more suitable multifunction display. In terms of housing dimensions, the new multifunction display is identical to the ST60 device series. Thus, the multifunction display can serve as a direct replacement for old and defective devices. By supporting old bus systems like NMEA0183 and SeaTalk, a bridge to the new world with NMEA2000 is provided, so that older systems can still be operated. The WLAN capability also allows to go completely new ways in signal transmission with connection e.g. to SignalK. Commercially there is a good selection of multifunction displays, but they are very limited in terms of expandability and adaptability to individual needs. You can only do things with the multifunction display for which the manufacturer has provided functions. Unfortunately, nothing can be modified or extended by the user. The goal of the whole development should be an open system where the user has access to all functions of the multifunctional display and can implement his own ideas by adapting the software and additional hardware. The standard electronics is designed in such a way that in the future it will be possible to replace it by other housings of other device series. Thus, maximum flexibility and openness is given.

Currently, the project is still in development.


In the design of the new display, emphasis was placed on the following points:

  • Standard size for a multifunctional display (110 x 110 mm)
  • Suitable for daylight
  • Waterproof
  • 6 keys
  • Support of the following bus systems:
    • NMEA0183
    • NMEA2000
    • SeaTalk
    • I2C
    • 1Wire
  • Low power consumption
  • WiFi-capable
  • Bluetooth-capable
  • Expandability via I2C bus and 1Wire
  • Hardware extensions via I / O port
  • Autarkic usable with battery pack for several days
  • Standard electronics for compatibility with other device series (NASA, Clipper, Navman, etc...)
  • Freely designable housing and therefore adaptable to other device series
  • Openness (OpenSource, OpenHardware)
  • Rebuildability with hobby means due to simple construction
  • Use of ready-made electronic modules
  • Adaptability to different needs
  • Software library for the Arduino IDE (similar to M5Stack)
  • Software updates via micro USB and WiFi

Video of the construction of the multifunctional display

Video to PCB


Specifically, the multifunction display was implemented with the following components and the following specification:

  • NodeMCU-32S as CPU unit
  • E-Ink display (400 x 300 pixels, 4.2″, suitable for daylight)
  • SeaTalk (full duplex)
  • NMEA 0183 (RX or TX, configurable)
  • SeaTalk (full duplex)
  • I2C
  • 1Wire
  • 8x I / O expansion port (internal)
  • 6x touch keys (swipe capable)
  • 2x digital out (12V, 4A)
  • 2x digital in (12V)
  • 2x Analog In (tank sensor 0...180 Ohm, battery etc.)
  • Battery monitor (12V voltage measurement)
  • Acoustic signal generator (buzzer)
  • Optical signal generator (red LED)
  • LED display lighting (red LEDs)
  • BME280 (temperature, air pressure, humidity)
  • GPS receiver (NEO-6M with internal mini GPS antenna)
  • WiFi 2.4GHz (HTTP, TCP)
  • Bluetooth
  • Power consumption approx. 2W (without backlight)
  • Power consumption approx. 3W (with backlight)
  • Battery deep discharge protection <9.0V (Deep Sleep, 0.2W)
  • Low Power Mode (Deep Sleep with WeakUp 0.2W, 15mA @ 12V)
  • Connections for optional LiPo battery pack (50Wh, approx. 24h self-sufficient)
  • Extension connections 8x digital IO, RX, TX, I2C, 5V 0.5A, GND

The next figure shows a schematic of the function blocks and their interconnection.

Fig. Functional diagram

The board is equipped with various SMD components and will therefore no longer be solderable without further ado. Some electronic modules can be assembled individually ( E-Ink-Display, NodeMCU-32S, BME280, GPS) The board will be offered for sale later fully assembled without electronic modules.

Fig. Front side of the circuit board

Fig. Rear of the circuit board


Fig. Electronics front

Fig. Electronics with e-ink display

Fig. Electronics rear

Fig. Front housing with display disc and contact springs for keyboard

Fig. Rear of the MFD

Circuit diagram

Possible uses

In principle, the following things could be realized with the multifunction display:

  • Instrument display of bus data from NMEA2000, NMEA0183, SeaTalk, WiFi
  • Gateway between NMEA2000, NMEA0183 and SeaTalk
  • Export of all sensor data via WiFi for tablets
  • SignalK connection
  • Weather display with weather history (BME280)
  • GPS display
  • Current position display in sea chart (with internet connection via OpenSeaMap)
  • Wind display (true wind)
  • Simple GPS autopilot (with DC motor as actuator)
  • Anchor watch
  • Battery monitor (with I2C current sensor also charge monitor)
  • Solar monitor (with I2C current sensor)
  • Motor diagnostics (temperature, speed)
  • Speedometer (with common pulse sensor)
  • AIS display graphically (with AIS receiver)
  • Info display for email, messenger services
  • Display for clock (UTC, local time), date, sunrise and sunset
  • Sailing timer (distance and time to start line)
  • Watch timer
  • Next Treckpoint indicator with XTR and audible alarm
  • Tank level indicator
  • Bilge monitoring with pump control
  • Alarm system with notification via WLAN including GPS tracker
  • Weather forecast (with internet connection)
  • Boat automation (with Sonoff components)
  • Reception of commands from a Bluetooth remote control with
  • Receiving Bluetooth wind sensor signals from Raymarine (if the signals can be decoded)
  • Control of audio media players (DLNA)
  • Firmware update via WiFi
  • and, and, and ....

In order to realize the possible applications, however, software is required that still has to be programmed and transferred to the multifunction display in the form of firmware. However, the firmware will not be able to implement all functions at the same time. Depending on the application, a suitable firmware is loaded onto the device via USB or WiFi connection and can then implement one or more functions. We hope that the multifunction display will find a lot of interest and that some will participate in the software development.

Current status

In the meantime, the first firmware has now been implemented. Thanks to the great software project NMEA2000 gateways from Andreas I was able to use core software that already covers many parts that I also needed for my firmware. The NMEA2000 gateway contains a complete gateway for converting the data between NMEA2000 and NMEA0183 and supports the transmission layers CAN bus, RS485, RS422, TCP and USB serial. The core software was written by Andreas for ESP32 microcontrollers in C ++ and was originally for one M5Stack Atom thought. Since the multifunction display also uses an ESP32 as a CPU, I decided to program extensions for Andreas Gateway software. This allows the hardware functionalities of the multifunction display to be used and data to be displayed. Andreas had to add various extensions and software functionalities in his software for me. Within a short time, a very useful firmware for the multifunction display was created with the following functionality:

  • Instrument display of bus data from NMEA2000, NMEA0183, WiFi, USB
  • Gateway between NMEA2000, NMEA0183
  • Generation of any user-defined XDR data for NMEA0183
  • WiFi access point for configuration
  • Web user interface (password protected)
  • Status line in the display
  • Red background lighting that can be switched on and off
  • Simple dashboard for displaying and diagnosing bus data
  • Firmware update via WiFi and USB
  • Export of all sensor data via WiFi for tablets
  • Weather display (BME280)
  • GPS display
  • Simple battery monitor (voltage display)

Currently, 4 display pages can be parameterized through the web configuration, which can be called up via swipe gestures. There are different types of display pages defined as follows:

  • Freely configurable display pages
    • On-value display
    • Two-value display
    • Three value display
    • Four-value display
  • Non-configurable display pages
    • Battery voltage indicator
    • True Wind with instrument display

All available bus data can then be brought to the display pages. The current firmware can be found at GitHub: https://github.com/norbert-walter/esp32-nmea2000

A detailed description of how to install the firmware is in the project for NMEA2000 gateway to find.





One of the biggest hurdles was the lighting of the e-ink display for night operation. It can only be illuminated from the front and requires special front glass that deflects the light coupled into the side via LEDs onto the e-ink display by 90 °. Making it yourself as a maker was not that easy. Industrially manufactured e-ink displays with lighting use front glasses that are microstructured. Such glasses cannot be bought in normal specialist shops. The aim was to apply the microstructuring yourself with the help of a laser. Laser devices that can be bought for makers do not have such a high resolution and we had to make some compromises with regard to efficiency and visibility. The best results came after many attempts a dithered laser point laser with an introduced point density gradient. A laser point is a disruptive body on the surface of the windshield, which deflects the light in all directions. The efficiency is not particularly good, since the light cannot be deflected in a directional manner and is only emitted from all sides in the room, so that only a small part of the scattered light can be used. We were able to achieve a minimum point size of approx. 200 µm with the laser. To create a gradient, we used a graphics program and created a gray level wedge with a 0… 12% gray component and then dithered it. The image resolution was 600 dpi. We used this image template for the laser process. Due to the high number of points, the laser process with a laser with XY traversing unit took a good 45 minutes, as the laser had to build up the image line by line. The result is impressive. The light is deflected as desired onto the surface of the e-ink display.

Fig.Laser points under the microscope (1% gray portion)

Fig .: Dithered image template for the laser process

Fig. E-Ink front lighting

A 3 mm thick Plexiglas pane is used as the front pane. The laser-structured side is on the outside. Alternatively, you can also use special Plexiglas panes for the advertising industry. This plexiglass is used to shine through advertising posters from behind and is often used in showcases or for illuminated pictures. This special Plexiglas is transparent and you can couple light into the front edge of the pane from the side, which is then scattered. The entire volume of the plexiglass acts as a diffuser. The Röhm company produces such special glasses under the name Plexiglas LED plate 0E010SM (4 mm). However, the lighting results are not as good as with the laser-structured windshield. The contrast of the illuminated display is too low and the picture is noisy.

Fig. Left laser-structured disk, right Röhm disk

In addition to protecting and lighting, the plexiglass pane has another task. It should protect the e-ink display from UV radiation (UVB, UVC) so that the display does not go blind. According to the specification, the e-ink display must not be exposed to direct sunlight or UV light. The reason for this is that the small pre-charged color balls in the display lose their charge due to UV radiation and can then no longer be aligned. Ordinary plexiglass has the useful property of suppressing UV light.

Fig. UV transmission of different glasses (2nd from plexiglass)


Fig.Multifunctional display with loaded demo nautical chart

Fig. Allen countersunk head screws as touch buttons

Fig. Viton seal as moisture protection

Fig.Raymarine standard mountings

Fig. Closing seal opposite the cockpit wall with 2mm thick Mosgummi

Fig. Total thickness corresponds to the original

Fig. 3D printing process

Fig. 3D front housing


Fig. Front housing with e-ink display


Fig. Illuminated e-ink display

IR remote


After Christian at Boot 2020 in connection with his plotter Had introduced a bluetooth remote control there is now a new IR remote control. It had been shown that Bluetooth is not that suitable for a remote control after all, since there were significant problems under Linux with the connection establishment and the remote control did not work as expected. The change to infrared enables the use of inexpensive electronic components in connection with a long running time, since no communication has to be continuously maintained with the IR remote control. The remote control works exactly like the remote controls in the home entertainment area. The only difference is that the remote control is waterproof. In order to simplify the implementation under Linux or in microcontroller environments, an intelligent one was added Receiver with a microcontroller that converts the received signals to I2C.

The remote control has the following specifications:

  • IR signals for data transmission at 36kHz
  • 14 keys with freely definable special functions
  • 2 powerful IR diodes
  • CR2032 head cell as power source
  • Inexpensive hardware with standard components
  • Waterproof, robust housing with hand cord
  • 2 different remote controls can be used simultaneously through coding
  • IR receiver with microcontroller for decoding the signals
  • Forwarding of received signals via I2C bus
  • Dimensions: (L x W x H) 140 x 45 x 25 mm
  • Weight: approx 100g
  • Costs. approx. 35 euros
  • Remote control wiring diagram
  • Circuit diagram for receiver

Possible applications:

  • Remote control for
    • plotter
    • Autopilot
    • Multifunction display
    • Audio
    • light
    • Automation