The Ski Speedometer is split into two different PCB’s, the main PCB and the LED circuit.

 

LED Circuit: The LED circuit contains five identical paths starting from the Pin Headers that connect to the main PCB and ending at the LED’s. Each path contains a 10k Ohm Resistor the limit the current entering the base of the transistor. An NPN transistor to provide more current to the LED, an LED, and a 330 Ohm Resistor.

 

Main PCB: The main PCB contains everything the Ski Speedometer needs to operate. It contains a Buck Converter, Arduino, OLED display and the L80-M39 GPS Module.

 

Arduino: The Arduino is powered off 4.5 V from the source and is the heart of the circuit. The Arduino powers the GPS of off the 3.3V Pin and connects the Rx and Tx pins on the GPS module to pins D2 and D3 on the Arduino. It also writes to the OLEDs SDA and SCL using pins A4 and A5.

 

Buck Converter: The buck converter has 4.5V entering it from the 3 AA batteries. The buck converter then steps the voltage down to 3.3V to power the OLED. Although the Arduino has a 3.3V pin, having the GPS and the OLED both running off it draws too much current for one pin, that’s why the buck converter is needed.

 

L80-M39 GPS Module: The GPS module is the reason that the ski speedometer works. It is fully functioning on its own but has no way to display the data, so the Arduino is needed to display information on the OLED. The GPS module works by transmitting and receiving signals from satellites using the Rx and Tx pins on the module. Once the GPS has connected to at least 3 satellites. The information will start being displayed on the OLED. Every time the GPS receives a new signal from the satellites, it’s given coordinates and a timestamp. The Arduino then takes the two readings and calculates the velocity.