signalk-rpi-ina219hat v0.7.2

signalk-raspberry-pi-ina219hat

ina219 current shunt and power monitor sensor information for SignalK (SK).

If you are uncomfortable with a soldering iron this project might not be for you.

By default these boards are set up for reporting current between -3.2 A to 3.2 A, Voltage 0-26 VDC, and Power. This is great for small systems, but the imputus for this project was identifying the level of individual consumers such as my fridge and heatpump. This has allowed a better understanding of battery sizing and energy use decisions.

It is adaptable to other circuit monitoring - for example I have used it to generate a power profile for my windlass using a 500A shunt.

There are commercially available circuit monitors, but most struggle with - for example - the 35A@12V load of a DC heat pump or the 60A@24V of a loaded windless.

Sure it is easy enough to get a spot measurement, but a detailed view of dutycycle of and power draw of the multispeed motors is very difficult.

Looking around I found a project from Jean-David Caprace, and combining that with available Pi Hats and some shunts produced the data flow I needed.

This plugin can be downloaded via the SignalK application.

Achnoldgements

This work is built on the excellent work of Jean-David Caprace https://github.com/jdcaprace and all who have contributed to the SignalK syetem.

Getting Started

You will need a raspberry pi with SignalK installed along with a ina219 sensor hat board.

The ina219 sensor

There are 2 hat boards that I am aware of:

The 3 channel hat from SB Components - https://www.amazon.com/gp/product/B08TC6CW9Y/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

The 4 channel hat from WaveShare - https://www.amazon.com/gp/product/B085WQCVVW/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

The boards are available from other stockests.

Using a multichannel hat allows more channels of measurement ot be performed and provides a potentially neater installation. The INA219 supports up to 16 devices on a single I2C bus.

The datasheet of the ina219 can be found here: https://www.ti.com/lit/ds/symlink/ina219.pdf

My 'issue' with the as supplied boards is that the current shunt is located on the PCB - meaning that all the current being senced needs to flow through the PCB. This is fine for low power applications, but makes measuring high power applications problamatic.

Current shunts are expressed as current for voltage signal, such as 50A/50mV. For example https://www.bluesea.com/products/category/6/19/Meters/Shunts.

To allow "easy" input of the shunt parameters this max current, sence voltage parameter pair is a convienient input format.

The INA219 is designed around a full scale measurement of 40^(gain step)mV. The code will select the gain step one larger than the expressed maximum sence voltage.

Higher gain steps produce lower resolution so the shunt should be the smallest possible to measure the desired current closely.

Connecting the Sensor

You need to make sure Raspberry Pi is turned off while doing this!

Before connecting the hat to the Pi the on PCB shunts need to be remove the on board shunts. Do this in and ESD safe environment.

This involvers soldering irons... molten metal.. and nast vapours.. if this scares you STOP. This project is not for you. Also this very ikely removes any warrently or support that might have possible come from the vendors.

For unused channels I suggest that you short the 3 inputs together with a short lenght of wire.

Plug in the hat and wire to the shunt.

For proper circuit current measurement the shunt should be connected to the high side of the circuit.

The 2 leads from the hot side of the circuit should be routed through inline fueses, I use 1A blade fuses.

Now you can power your Pi and do the configuration.

Configuring the Plugin.

In order to use the sensor, the i2c bus must be enabled on your rasbperry pi. This can be accomplished using "sudo raspi-config". Here is a example of how to do this - https://www.raspberrypi-spy.co.uk/2014/11/enabling-the-i2c-interface-on-the-raspberry-pi/

In SignalK admin mode install the plugin from the app store.

Enable the desired channels.

And configure the shut parameters. These will be written on the shunt and be of the form..

• 100A/50mv for this enter 100 and 50, the fields are numeric and do not need the A and mv.

If you want to leave the default resistor on and measure low currents the values to enter are 3 and 300.

Select the I2C address for that channel, For the available hats this is 0x40 through 0x44, but I have allowed for all the possible I2C addresses in case someone makes a 16 channel board.

Select the I2C bus. All the hats connect to I2C-1, but RPI3 and 4 have several available I2C busses.

Check the box if it is a 24V power circuit.

Enter the measurement frequency - Periods of less than 0.5s can cause system instability due to load.

Now if you want to add another measurement channel you can. You can infact add the same measurement channel a second time and you will get a second output of almost the same data.

Troubleshooting

When you first start SK, you should see one of two things in the /var/log/syslog; ina219 initialization succeeded or ina219 initialization failed along with details of the failure.

If the sensor isn't found you can run ls /dev/*i2c* which should return /dev/i2c-1. If it doesnt return then make sure that the i2c bus is enabled using raspi-config.

You can also download the i2c-tools by running sudo apt-get install -y i2c-tools. Once those are installed you can run i2cdetect -y 1. You should see the ina219 detected as address 0x77. If the sensor isn't detected then go back and check the sensor wiring.

A note on Sampling

Sampling is just that .. a way of reducing data. One hopes that the sample catches reality. But you should be aware in the ways in which it can fail In INA219 takes a snapshot of the voltage and current, at an interval of your choosing. This snapshot is taken over 0.068s at a (default) 5s. For steady state loads this is fine. But it might miss - or catch - something like a motor starting. For these cases it is better to use a meter with peak ( max and min ) capture. Peak capture is not the target for this device.

Authors

• Brian Scally - Author of this plugin