Wireless Temperature Sensor

About me

I am a student of Brno University of Technology in Czech Republic. I am not so experienced with electronic and this is my first larger project. That is really challenging to me.

About project

Device should be able to meassure ambient temperature and be able to connect and measure any industry sensor, which works on 0-10 V or 4-20 mA principe. Data will be measured once per time, lets say once per hour, and should be transfered wirelessly to the cloud, where should be visualised into graphs, so user can see them easily. Also, project should be battery powered, which means the module should consume as little battery capacity as possible. The main element of this project is ESP32, wireless and bluetooth module. Module will be connected to the Wi-Fi, therefore user should be able to change credientials. Also, user should be able to change time of measurement period. Thats why serial pins of the module are exposed. Afterwards, user will connect USB-UART converter to the pins, so he can comunicate with module. Last thing module should be able to do is to report battery level to the user.

First of all, I started thinking, which batteries will be used. Requirements for the battery are: enough capacity to power the device for at least half a year, to supply the voltage module needs. My first thinking was to use AAA batteries, but they have small capacity and take much space on my PCB. LiOn batteries were the second choice. I started with 18650 LiOn, which was 4,2 V 3600 mAh capacity. Problem was I needed to use stabilizer, which consumed much capacity of the battery while the module was not measuring. I ended up with 18650 LiFePo4, which has got maximum voltage of 3,6 V, which is acceptable my the module and has capacity of 1800 mAh.

Then, I needed to choose right temperature sensor. There is a plenty of them on the internet. I needed the one, which will be as exact as possible, will not be expensive and will consume as little capacity as possible. The DS18B20 was right choice.

After that I started with projecting of 4-20 mA and 0-10 V inputs. Inputs for the sensors will be connected to the module through the connectors on the board. Output of the sensors will be measured by using ADC of ESP32. Powering up sensors is realised by using step up convertor MT3608, which can boost voltage up to 28 V.

Also, I need to program the ESP32 somehow. Thats why I put two tacticle switches on the board, so I can put the module to the flashing mode.

If i take all of those statements in mind, module should be able to work almost 1 year by using only one battery with capacity of 1800 mAh. Thats really impressive.

Support from PCBWay would be a big help to me, because i need qualite PCB, which is not as easy to get as with PCBWAY.com.

Thank you!