relier - acquisition system

Open {re}design of an acquisition system for {l}aboratory tests on {i}nternal {er}osion in soils

Project developed by Ricardo Correia dos Santos at Laboratório Nacional de Engenharia Civil - LNEC, in Lisbon, Portugal

relier AS is an open 'low budget' acquisition system (hardware and software), that automatically collects data from multiple analog and digital output sensors, which are commonly used in laboratory tests on soil erosion.

Some project videos

| Sensors overview and GUI | Assembly of acquisition system| |--------------------------|--------------| | | |

Is this for me?

If you need to do a similar project, you just need to have some DIY skills, for scrapping some materials, figuring out how to assemble some things together, and investigate how some components work. The instructions given here should also be taken more like guidelines based on "what I can do with the materials I have". If you do not have the exact same hardware components (sensors, ADC, level shifter, touchscreen...), yours will surely work a little different, but as they should do the same things, there will be similarities too. You may have to adjust the code and/or the connections to meet your needs.

Feel free to contact me if you manage to get it working with different components, so these instructions can be improved and be more helpful.

1. Hardware

The hardware components required to make the relier acquisition system are indicated in this chapter. Instructions about the way those components are connected are presented. For reference, some links and prices of each component are indicated.

The Hardware is composed by the:

• Aquisition box (server, touchscreen, custom PCB HAT and connection plugs);
• Sensors (4 with analog outputs and 3 with digital outputs).

1.1. Aquisition Box

The main items of the acquisition box are the following:

• Server: Raspberry Pi 3 model B;
• 2.8" Touchscreen: Nextion HMI display;
• Custom PCB HAT: made specifically for this project (details about the PCB design).

All these main components are placed inside an aluminum enclosure box, in which openings were made, for the power supply, display, and connections. Peripheral inputs to collect sensors data, and peripheral outputs (USB ports) to storage sensors data, are also available. The acquisition box is powered solely through the power supply connected to the Raspberry Pi (output: DC5V, 2A).

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https://i.imgur.com/RYcSZy1.jpg

You can find more pictures and an overview video in the Media folder of this GitHub repository.

1.2. Sensors

The relier acquisition system is prepared to simultaneously collect data from the following 'low cost' sensors:

• Channels 0-2 : Analog pressure transducer sensor (Piezometric water pressure);
• Channel 3 : Waterproof DS18B20 Sensor (Water temperature);
• Channel 4 : Analog turbidity sensor (Water turbidity);
• Channel 5 : Turbine flow Sensor (Water flow); and
• BME280 sensor (Air temperature, humidity and pressure).

Most of the sensors are connected using the 6 mini aviator (circular) plugs that are linked to the custom PCB HAT. An exception is the BME280 chip, which can be soldered directly to the custom PCB or using a short 4 wires cable. This last option is preferable, because, ideally, to monitor the ambient air temperature/humidity/pressure, the BME280 should be placed outside the AS box (or at least, inside the box, but near large openings), to avoid the heat generated by the touchscreen and by Raspberry Pi!

Note: relier was designed to use low budget sensors. Thus, initially, only allowed the use of a turbine type flowmeter. However, since LNEC laboratory owns an Eletromagnetic type flowmeter (Danfoss MAGFLO 5000), the software was adapted to also allow its use (communication via USB serial port of the Raspberry Pi). Please beware that such devices are much expensive (1500-2000 €) than turbine flowmeters (< 20 €). The user should choose, in each test, one of these types of flowmeter.

The following table indicates the advantages and drawbacks of each type of flowmeter allowed.

Flowmeter type | |Advantages | Drawbacks | -------------------|----------------------------------------|-------------------------------------------------|----------------------------------------------------------------------------| Turbine | |Cheap; Fast response to sudden drop/rise of flow | Low accuracy for low flow rates (may be even unable to detect low flow) | Eletromagnetic | |Better accuracy, even for low flow rates | Expensive; Somewhat smother variation of flow, for sudden drop/rise of flow|

1.3. Bill of materials (BOM)

The following tables show the bill of materials (BOM) of the items used in relier AS, as well as their main specs and indicative prices (in January 2019).

Acquisition Box

| Qt | €/un* | Ʃ € | Photo | Description | Notes | |---------|----------|----------|---------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------| | 1 | 35 | 35 | |Raspberry pi 3B | Server | | 1 | 16.2 | 16.2 | |Nextion HMI touch display 2.8" | Graphical User Interface (GUI) | | 1 | 6.2 | 6.2 | |Aluminium enclosure box (88x38x100mm) | Aluminium enclosure box | | 2 | 10 | 20 | |Micro SD card (>16GB) | One for the raspberry pi and another for the Nextion display (during installation) | | 1 | 8 | 8 | |Raspberry Pi Power Supply | Power up the raspberry pi and the sensors | | 1 | 1 | 1 | |Raspberry pi Hat - Custom PBC: | Interlinks server, touchscreen and the sensors | | 1 | 1.4 | 1.4 | |► 16 Bit I2C ADS1115 Module ADC 4 channel with Pro Gain Amplifier | Analog to Digital conversion for analog sensors | | 1 | 0.3 | 0.3 |![](Media/ima