USB-Interfaced Wireless Sensor for Humidity and Temperature

The project is an improved version of the firmware-only USB implementation of Remote Sensor with the main change of replacing the analog sensors with a Sensirion SHT11 digital temperature and humidity sensor.

No calibration was required for this device since the design of the transmitter was smaller and simpler. An ATtiny45 microcontroller comprises the sensor unit along with 868MHz transceiver module and the SHT11 sensor. Two AA cells are used to power the sensor unit which is expected to provide a battery life of 1 year. The same RFM12 module is used by the receiver together with an ATmega8 microcontroller. This will transmit the received data through USB to the PC. The received data can be written in CSV format by the host software and also in a one-line per value format for integration into the cricket graphing system.

The ATmega8 uses only a few of the I/O ports where two are for audio, two for LEDs, and one for a pushbutton. This enables the use of another controller easily that has an 8-bit timer with two PWM channels. Some volatile variables are awaited to be changed by the main code.

Rest of the project