Instrument panel signal and vibration reader for heavy-duty vehicles, for an industrial institute in Thailand

How the brief came about

The brief for this case was to turn values from a heavy-duty vehicle's instrument panel into digital data that can be viewed as charts over time. The required values include engine speed, oil pressure, engine temperature, hydraulic temperature, fuel level and voltage. The customer wanted to see all values on a single screen, along with the vehicle's vibration values.

A needle-type instrument panel shows only the value at that moment. If the temperature rises briefly or oil pressure drops momentarily, the driver may not see it. Once every value is stored as a chart over time, engineers can see relationships between values, such as temperature and engine speed, and use them as a starting point for analysing problems.

Requirements and constraints

The signal reader has to accept several signal types from the same vehicle and work with the vehicle's power system. The main requirements and constraints according to the project documents are as follows.

• Accept 7 Analog voltage channels of 0–10 V and 1 Analog current channel of 4–20 mA
• Accept 4 Digital channels of 5 V Active Low (active when the signal is at zero) for on/off signals
• Measure vibration on 3 axes and read one additional temperature value
• Run on the vehicle's 24 V power, with the design documents setting out an approach for installation on tractors used in factories or sugarcane fields
• Display charts of 15 sensor values on a single screen, with users able to choose to hide or show the chart of each sensor

How does this signal reader read values from the vehicle's instrument panel?

This signal reader connects to the existing signal wires of the vehicle's instrument panel and sensors, then reads every channel at the same time. The signal input circuit separates channels by signal type, the ESP32 reads values from the circuit, and the NVIDIA Jetson Nano board stores the values and displays the charts. Users therefore do not need to note down values from the panel's needles themselves.

The current signal passes through a converter module to become a voltage before entering the circuit, so every Analog channel receives signals in the same format. The roles are clearly separated: the ESP32 reads signals, while the NVIDIA Jetson Nano stores data and displays results.

1. 1

   Measuring instrument panel signals on site

   We measured the electrical signals of the instrument panel on site, namely engine speed (Tacho Meter), oil pressure, hydraulic temperature, engine temperature, fuel level and voltage, in order to design the circuit to accept signals in the correct range.

2. 2

   Bringing signals into the circuit

   The circuit receives Analog and Digital signals as listed in the requirements above. Each channel connects to the existing signal wire of the instrument panel or sensor.

3. 3

   Measuring vibration and temperature

   The 3-axis Accelerometer measures vibration along the x, y and z axes, while the temperature sensor reads one additional value.

4. 4

   ESP32 and NVIDIA Jetson Nano store the data

   The ESP32 reads values from the circuit and passes them to the NVIDIA Jetson Nano board running Ubuntu. A program written in Python receives the values and stores them in a SQLite database.

5. 5

   Viewing charts through the web app

   Users connect a display via an HDMI cable, open a web browser on the device, and view line charts of 15 sensor values. The horizontal axis is time, the vertical axis is the value read, and users can click to hide sensors they do not want to view.

Deliverables

We delivered the signal reader with software on the NVIDIA Jetson Nano board and a user manual. The items according to the scope of work are as follows.

• Signal input circuit as listed in the requirements, with enclosure and connectors
• Current-to-voltage signal converter module, 3-axis Accelerometer and temperature sensor
• Configuration of the Kernel (the operating system core) and libraries on the NVIDIA Jetson Nano board
• Controller and signal interface section
• Web app with line charts of 15 sensor values, storing data in an on-device SQLite database
• The full software set is written in Arduino, Python and PHP
• User manual, from connecting the display to opening the chart page

Confirmed results at project close

The confirmed result is that we closed out the work according to the scope of work and delivered a user manual. The delivered set reads 8 Analog channels and 4 Digital channels, then displays 15 sensor values as line charts over time on the NVIDIA Jetson Nano board.

During handover, we tested signal reading with a set of instrument gauges provided on site, because the vehicle's actual sensors were not yet available for testing. This result therefore confirms the operation of the circuit and the chart page, but it is not yet a result from use on an actual vehicle.

What we learned

This work offers 3 principles for reading signals from existing vehicles or machines.

• Start from a list of signals measured on the real equipment. This list must include the signal type, value range and number of channels for each value, because the signal input circuit, signal converter module and chart page are all designed from it.
• Convert signals into a single format right from the input. When the current signal is converted to a voltage before entering the circuit, every Analog channel can use the same type of input circuit and be read in the same way.
• Separate circuit testing from testing values in real use. Testing with a signal source on a bench confirms that the circuit can read signals, while values from real use must be confirmed with the sensors of the real equipment. An acceptance test plan should therefore be set, and sensors for testing prepared, from the start.

How can you apply this approach to your vehicle or machine?

If your vehicle or machine has an instrument panel and sensors that send voltage, current or on/off signals, you can use the same approach as this case: read signals from the existing wires, store the values on a unit in the vehicle, and display them as charts over time. What needs adapting depends on the signal types, the power system and the acceptance test method.

• Make a complete list of the signals you need to read, with the signal type and range of each value
• Check the power system of the vehicle or machine and the site conditions, such as dust, heat and vibration, which affect the choice of enclosure and how the equipment is mounted
• Prepare a real vehicle or real sensors for acceptance testing, and define which values must match which