mirror of
https://github.com/MOSH-Insa-Toulouse/5ISS-2024-2025-MARIN--MULLER-BOUJON.git
synced 2025-06-08 14:00:49 +02:00
112 lines
6.1 KiB
Markdown
112 lines
6.1 KiB
Markdown
## Embedded
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[Full Software design here](hardware)
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We made a breadboard using various components like a *LoRa UART* [RN2483A](https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/RN2483-Low-Power-Long-Range-LoRa-Technology-Transceiver-Module-DS50002346F.pdf), an [SSD1306](https://cdn-shop.adafruit.com/datasheets/SSD1306.pdf) I2C Screen and a [Gaz Sensor MQ5](https://wiki.seeedstudio.com/Grove-Gas_Sensor-MQ5/) from Seeed Studio. The goal would be to communicate using the LoRa chip to [ChirpStack](https://www.chirpstack.io/) by sending the sensor data directly to the gateway. We decided to use an ESP32 for this project, because it has a wide variety of pins that can be dynamic allocated on each gpio. Plus, espidf is a framework we are familiar with.
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## Hardware
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[Full LTSpice simulation and EasyEDA design here](hardware)
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**Amplifier Design**
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Gas sensor Characteristics:
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The gas sensor has an impedance of several gigaohms, requiring signal amplification. But amplification increases signal noise as well, hence the conditioning circuit needs several filters to improve signal quality:
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- Filter for the high-frequency noise.
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- Filter for the 50Hz outlet noise.
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- Filter for the ADC sampling noise.
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When designing the signal conditioning circuit two types of amplifiers were considered: a standard low-cost amplifier and a costly very low offset amplifier (LT1050).
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We performed simulations on both and found that the LTC1050, better suited our application (as expected) because a high offset could significantly affect the accuracy of the gas sensor
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*Image: LTSpice Simulation of the circuit comparing the two OpAmps*
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Filters Specifications:
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- First Filter: Cutoff frequency at 16 Hz.
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- Second Filter: Cutoff frequency at 1.5 Hz.
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- Third Filter: Cutoff frequency at 1.6 kHz.
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*Image: LTSpice Schematic of the cirtuit with the 3 filters outlined in blue*
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Gas sensor model LTSpice simulations:
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In order to simulate the entire signal conditioning circuit, we needed an electrical model of the gas sensor, described as follow:
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*Image: Gas sensor electrical model schematic*
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*Image: LTSpice Simulation of the gas sensor model without 50Hz filtering*
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*Image: LTSpice Simulation of the gas sensor model with 50Hz filtering*
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Based on the above-cited images we can clearly see why the filters (and particularly the 50Hz filter) are useful.
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The goal in this part is to create a fully working PCB with everything we designed so far. Our own gaz sensor will be used. The first step would be to emulate on **LTSpice** the behavior of such a sensor. With this we can then design a board with the correct schematic on **EasyEDA**.
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**Specifications**
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As we were experienced with PCB design, we decided to directly dive into making the hardware based on what features we wanted:
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- ESP32 based system (as we were at ease with the esp-idf framework)
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- Gas sensor and conditioning circuitry
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- SX1278 LoRa Module as we extensively used it in our innovative project
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- LDL117 low dropout LDO to power the system efficiently on a single cell 3.7V LiPo battery
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- A 2.7kHz buzzer to alarm users if gas levels are above a certain threashold
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- The same SSD1306 I2C Oled Display that we used during the prototyping phase in order to diplay information to users locally
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- A 12650 standard Li-Ion battery holder
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- A button for easy mode switching and styreamlined user experience
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- Bonus: BME MEMS Humidity sensor to provide additional metrics to the users.
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*Image: Complete Schematic with all the Features Listed Above*
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To facilitate and accelerate schematic design, we chose components that we were already familiar with from past projects. This enabled us to skip some prototyping steps.
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We also considered the assembly process during component selection, particularly focusing on component package types to ease the soldering process.
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**Routing the PCB**
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- Ground and vcc plane
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- Dynamic track width to handle different currents
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- Thoughtfull component placement for easy soldering
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*Image: From Left to Right: Top Plane, Bottom Plane and Focus on Dynamic Route Width*
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**PCB Manufacturing**
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We manufactured the PCB using JLCPCB as we am very familiar with the platform (from personnal and semester project). After two weeks we received the PCB and all the electronic components.
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*Image: Manufactured PCBs*
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*Image: Electronic Components*
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Due to lack of time, we couldn’t assemble the PCB during the project time. However, we plan to complete the assembly in our personal time because it was a very interesting project.
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## Node Red
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[Full Node-Red setup here](node-red)
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We would need to create a node-red flow to actually gather the data and show it on a dashboard. To do this we would have to connect using a MQTT Broker, Chirpstack has the ability to resend, via a given topic the data gathered by the device.
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## App Inventor
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Using the [AppInventor](https://ai2.appinventor.mit.edu/) we have designed a mobile application that can directly communicate with a bluetooth receiver and power on a LED. You can see the application from the files as well as the source file for the embedded part.
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