Hidden Talents
Hi everyone, I am Eric. I am a mechatronics/computer engineer and am always fascinated by solving problems with automation approaches. I like to look around in my environment and imagine how everyday processes can be automated or what is possible in case certain information is collected automatically. Of course, not everything is practical or useful, but sometimes I have good ideas that are not too hard to implement.
One of these ideas was a WiFi-attached postbox sensor. The idea for that came to my mind during the application process for my master’s program. A few universities still send their acceptance letters via traditional mail and not electronically. So I went day after day to my postbox only to find it empty. So, I thought, if I cannot receive mail electronically, I can at least notify myself electronically when something is waiting for me in the postbox.
For this project, I wanted to experiment a bit with wireless communication, especially WiFi, because it makes the system quite easy to install. Also, I did not want to spend too much money, but I knew that having some spare parts would be handy for testing and in case I broke something. So, I ended with a budget of around 50 € (single systems cost only around 10 €).
For the development, there were primarily 3 functional components to consider: the sensing mechanism, the telemetry unit, and the power supply. For the power supply, I quickly realized that the system must be battery-powered to keep the flexible installation. For the telemetry unit, I had a quite old but popular microcontroller in mind that had an integrated WiFi module (the ESP8266) and for the sensing principle, I thought of multiple solutions. I considered light barriers, simple photo resistors, and capacitive sensors but at the end of the day, the most practical solution was simple mechanical switches, because they only draw power when activated. Since the system is battery-powered, the energy consumption was of major importance. If I had to go to the postbox every day to change the battery, the whole purpose would be gone.
In the final system, the microcontroller is, most of the time, in deep sleep mode. Only when the mailman opens the postbox do the switches send a short wake-up pulse, so that the controller connects to the WiFi, sends an e-mail, and goes back to deep sleep. With that, I was able to achieve an operating time of around 5 weeks with a single charge.
With the Hans-Peter Wild Scholarship, I was able to buy a solar panel to recharge the battery automatically. After a while, I reused the solar panel for a solar-powered phone charger, another tinker project of mine where I wanted to learn more about currently used charging protocols. Besides that, I planned on buying a 3D printer to make proper housing for the system, but since my room in Heidelberg is not very big and quite stuffed with other “spare parts” this wish is currently postponed.
