Case study: bachelor thesis / IoT prototype

IoT prototype for monitoring CO and LPG in garages

The bachelor thesis at the Faculty of Information Technology, Brno University of Technology came from my own idea for a wireless sensor network prototype for monitoring carbon monoxide and LPG in garages according to ČSN 73 6058. The result was a designed, built and programmed measuring node with ZigBee communication.

Bachelor thesis prototype for wireless CO and LPG monitoring in garages
Problem

Underground garages need pollutant monitoring

I built the bachelor thesis topic on my own idea: solve a practical access problem for LPG vehicles in underground public garages. Many garages had a traffic sign banning LPG vehicles. To remove that restriction technically, an operator needed to monitor pollutant concentrations in the air and react according to ČSN 73 6058.

The standard works with carbon monoxide (CO), nitrogen oxides (NOx), benzene (C6H6), dust particles, soot and volatile substances from operating fluids in garages. CO is the decisive gas for public garages. For garages that allow LPG vehicles, monitoring propane-butane (C3H8-C4H10) also makes sense because it forms an explosive mixture with air.

The practical task was to design a device that measures CO and LPG, indicates state locally, sends values wirelessly and can serve as a base for another product version for public garages or home garages.

Solution

Wireless measuring node with CO and LPG sensors

I built a measuring device prototype with a custom PCB, power supply section, MQ-6 sensor for LPG, MQ-7 sensor for carbon monoxide, LED signalling, USB/UART connection and a ZigBit ATZB-24-A2 wireless module. The firmware ran on the BitCloud stack and used ZigBee / IEEE 802.15.4 communication.

The network used a coordinator and routers. A router measured concentrations, processed ADC values, indicated status locally with LEDs and sent data to the coordinator. The coordinator could pass the data to a higher-level system, for example ventilation control or statistics collection.

I handled the full product path on the prototype: electrical schematic, component selection, PCB design, hand soldering, device bring-up and all firmware. The firmware set included PCB testing, sensor preheating, coordinator operation and router operation.

The hardest part was connecting hardware and firmware into one working unit. The PCB had to work with three voltage levels, switch sensor power, connect ZigBit to a computer through FT232RL, read the ADC, drive LED signalling and send acknowledged data through the ZigBee network. BitCloud stack 1.14.0 also had build issues with Atmel Studio 6, so I had to trace and work around them.

01The sensor node measured CO and LPG in regular cycles.
02The firmware averaged values, handled different sensor behaviour and signalled state on the device.
03Measured data was sent through the ZigBee network to the coordinator with transfer acknowledgement.
Result

Working base for another IoT device

The result was a designed, built and programmed prototype. The work covered the whole chain from idea and component choices through PCB design and hand assembly to firmware for PCB testing, sensor preheating, coordinator operation and router operation.

The prototype showed the full path from a concrete environment requirement to embedded software and wireless communication. The same type of work applies today to internal tools, IoT prototypes, operational automation, device data collection and connecting measurements to a web or mobile application.

Project examples

Prototype design examples

Crops from the bachelor thesis show the power design, converter, device schematic, PCB and logical parts of the hardware.

Figure 4.2 power supply schematic for the CO and LPG IoT monitoring prototype
Figure 4.2: Device power supply schematic.
Figure 4.3 switched step-down voltage converter for the CO sensor
Figure 4.3: Switched step-down voltage converter.
Figure 4.6 FT232RL converter wiring between USB and ZigBit UART
Figure 4.6: Converter wiring.
Figure B.1 device schematic with ZigBit ATZB-24-A2 and MQ-6 MQ-7 sensors
Figure B.1: Device schematic.
Figure B.2 PCB layout for the CO and LPG monitoring prototype
Figure B.2: PCB layout.
Figure B.3 logical parts of the device with CO sensor LPG sensor and ZigBit module
Figure B.3: Logical parts of the device.
Sources

Sources used in the bachelor thesis

  • ENERGIZER HOLDINGS: Ultimate Lithium Batteries. 2012.
  • MC34063A design tool. 2013. Link
  • ATMEL CORPORATION: Atmel AVR2054: Serial Bootloader User Guide. 2011.
  • ATMEL CORPORATION: ZigBit 2.4 GHz Wireless Modules. 2009.
  • ATMEL CORPORATION: 8-bit Atmel Microcontroller with 64K/128K/256K Bytes In-System Programmable Flash. 2012.
  • ATMEL CORPORATION: Atmel AVR2051: Atmel BitCloud SerialNet: User Guide. 2012.
  • ATMEL CORPORATION: Atmel AVR2050: Atmel BitCloud: Developer Guide. 2012.
  • DIODES INCORPORATED: AP2141/AP2151: 0.5A single Channel Current-Limited power switch. 2009. Link
  • Farahani, S.: ZigBee Wireless Networks and Transceivers. Elsevier Ltd, 2008.
  • FLAGA S.R.O.: Safety data sheet: Propane-butane. 2013.
  • FTDI: USB UART IC FT232R. 2012. Link
  • HANWEI SENSORS: Technical data MQ-6 GAS SENSOR. 2007. Link
  • HANWEI SENSORS: Technical data MQ-7 GAS SENSOR. 2007. Link
  • Mikulčák, J.; Široký, B.; Šůla, J.; et al.: Mathematical, physical and chemical tables for secondary schools. PROMETHEUS, 2011.
  • Plíva, Z.: EAGLE prakticky: řešení problémů při běžné práci. BEN, 2007.
  • PRIMAGAS S.R.O.: Safety data sheet: LPG motor fuel. 2012. Link
  • Czech Republic: Decree No. 268/2011 Coll. 2011. Link
  • Czech Republic: Decree No. 23/2008 Coll. 2008. Link
  • STMICROELECTRONICS: DC/DC converter control circuits. 2007.
  • TEXAS INSTRUMENTS: LP2950/LP2951 Series of Adjustable Micropower Voltage Regulators. 2011.
  • TEXAS INSTRUMENTS: Current-Limited, Power-Distribution Switches. 2011.
  • ÖNORM H 6003: Lüftungstechnische Anlagen für Garagen - Grundlagen, Planung, Dimensionierung. 1997.
  • ČSN 73 6058: Jednotlivé, řadové a hromadné garáže. Czech Office for Standards, Metrology and Testing, 2011.

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