USB Interfaced Indoor/Outdoor Thermometer

The project demonstrates the USB peripheral on the PIC18F2550 microcontroller by building a thermometer that can measure the indoor and outdoor temperature.

The PIC18F2550 microcontroller used in the project is a smaller 28-pin version that reads the sensor data and sends it to the PC through the virtual serial port like USB interface. Temperature sensors are used although other analog sensors can be included. All components are available in through-hole versions even if the PCB uses surface mount parts.

The Microchip TC1047A temperature sensor is used as the indoor temperature sensor that is soldered to the board physically which causes it to run a few degrees hotter than room temperature. The PIC from the power supply is decoupled by a 0.1uf capacitor between power and ground. A 48MHz internal clock is generated using a 20MHz crystal together with two 27pf capacitors. An outdoor temperature probe uses a header for connection.

To emulate a serial port, the CDC USB class is used by the firmware which is made up of 3 sections including the USB driver, a service routine, and a main routine. The firmware sets all configuration bits correctly as well as device programming.

Rest of the project