A friend of mine asked me to design a basic variometer for para gliding.
He wanted a standalone device "beeping" when climbing.
Here is the prototype (difficult to make more simple..) :
- an ESP32 Lolin Lite board
- a BMP280 sensor
- a 3.3V buzzer
and no solder, no PCB till now
Of course a B4A App as I couldn't resist to design something a little more complicated... But bear in mind that the device really works standalone. The App is totally optionnal and transparent (no interface for binding, all automatic !)
I took my scooter to ride the 2 roads down/up and back down/up.
Variation of altitude is displayed in real time, using @Johan Schoeman excellent library
I have added a menu to open Google Earth and display the track. (thank you @agraham )
The altitude is given @1Hz by the sensor via BLE and lat/Lon by the GPS into the smartphone.
A parameter allows to tune the altitude and correct the offset between sensor and Google Earth.
The result is quite impressive. This tiny sensor is really accurate and stable (+- 50cm max).
As you can see, I directly powered the BMP280 with 2 IO pins of the ESP32 It's possible because the BMP only sinks 5µA... + and Gnd are thus provided by 2 IO pins. If I switch them as inputs then the BMP is totally off. This should be nice when the ESP will be in deepsleep to protect the battery !
Similarly the buzzer is sinking 14mA wich is a little too high for one single IO pin (12 mA max)... so I used 2 pins to drive the buzzer directly and safely.
The Lolin32 board allows to plug a lipo bat and has a charger embedded (charge it or power it with a 5V USB charger).
As such this design is really my most minimalistic one : (three componants !) and soooooo cheap (<10$)