WHAT’S INSIDE ?

The BeMap device is a bike lamp featuring GPS tracking and sensors measuring pollution along your cycling route. Cyclists can gather data about their surroundings in order to chose their path to work according to pollution values.

The basic configuration features Swiss sensors SGX MiCS-4514 used for measuring NO2 and CO levels, and the Sensirion SHT21 Humidity and Temperature Sensor IC.

The device is based on an Arduino Leonardo and sensors can communicate through an I2C data bus or analog pin. Users can modify and upgrade their own device as it is open-source.

hardware

Download the schematics and gerber files !

THE STORY BEHIND THE ELECTRONICS

Deep in the philosophy of our device we needed to find a way to make the device transparent for the user. Transparent in term of reliability so you won’t ever have to worry about it but also transparent in term of hardware and technology.

When you add to that the fact that we are now living in a world full of tinkers and makers of all kinds, we concluded that it would best suited for our device to be based on an existing open-sourced platform, you guessed it: Arduino.

 

Soldering

solder

To make our communication with the PC through a serial connection, we wanted a platform able to handle the usb protocol in a single chip so we settled on the Atmega32u4 as known as Leonardo for all the Arduino aficionados out there.

Now that we had our main processing unit laid out we had to get all the remaining components, and for that we use three main filters: availability, price and performance. A compromise between those three criteria always worked out for us.

With that in mind we needed a GPS “name of GPS here”, which communicate with the remaining available UART port on the Atmega with the NMEA protocol, we needed an accelerometer, we chose the ADXL”number here” because the Arduino library was allready existing, we needed some kind of memory, we chose flash, for it’s reliability, form factor and it’s storage/price ratio.

For the power supply we needed something rechargeable to stay in line with what we are trying to achieve, but also lightweight and with a decent autonomy, that leaves us with the LiPos which we implemented with the help of two chips, a switch mode DC-DC converter (TPS61200) and a one cell LiPo charger (MCP73833).

In the end the only part missing was the set of sensors needed to measure the pollution/environmental data and for that we decided to have one chip to measure temperature and humidity (Sensirion “numberhere”) and another chip to measure CO and NOx (“SGX number of chip here”). Measuring pollution in a bike lamp is quite a challenge, since “lab accurate” sensors don’t come in a small enough form factor, also power consumption in catalytic devices such as the one we chose is quite a hassle to be handeled on a small LiPo. We had to make a decision and try with a sensor that on paper was not ideal to make it work for us in our device.

Now you would tell me, wait a minute, there is no light source yet, how do you call that a “lamp”. Well you would be right, but on the right angle board in the front of the device along side of the SGX sensor we shoved a really bright LED which has a stunning Lumen/Amps ratio to keep you safe on your bike in the darkest nights of winter.