Mavrk wireless weather station communication system
By: Bill Gesner
Goal Receive weather information from two RJ-11 connectors(phone jacks). Transmit the data wirelessly from the Texas Instrument micro Mavrk to a Texas Instrument Mavrk. Send the data to a PC and a secondary embedded device.
Weather Meter Design Rain Gauge: The rain meter pools water which causes a circuit to close once per 0.011” of rain. Anemometer: The speed of the wind is recorded by closing a circuit once per rotation. Wind Direction: The direction of the wind causes a change in resistance across the output.
Rain Gauge Input A digital input port was used to detect the current state of the circuit. The number of times the circuit was closed was counted. Once every two seconds the count was transmitted wirelessly to the base station. The data was sent to the PC via USB as well as the serial port.
Wind Speed Input Similar to the Rain gauge method. The Anemometer circuit closes once per revolution. A wind speed of 2.4 km/h causes the switch to close once per second. The amount of times the Anemometer circuit closed was counted and transmitted once every five seconds.
Wind Vane Input The direction of the wind alters the resistance across the wind vane output. An analog to digital converter input was used to detect the voltage drop across the wind vane which was connected in series to a 10kOhm resistor. The value of the ADC was transmitted wirelessly once every two seconds.
Temperature A built in temperature sensor is included on the micro Mavrk. The temperature sensor output is connected to the ADC similar to the wind vane input Functionality of the temperature sensor is optional to allow for the possibility of an extra ADC input.
Humidity A secondary chip can be attached to the micro Mavrk to add humidity detection. The TMP-112 replaces the output of the built in temperature sensor with the output of a humidity sensor. The temperature data is then available via I2C with more precision.
Light The brightness in the room can be read from the micro Mavrk. This functionality can be enabled using the standard micro Mavrk or the TMP-112.
Output The output of the data is then sent to the Texas Instrument demonstration software “App Monitor”. This displays all built in functionality such as temperature, humidity, and light levels. The raw data is also transmitted serially via UART.
UART output packet structure The data sent to secondary embedded hardware required a data structure to ensure valid transmission. In total 7 bytes were transmitted 2 byte header 1 byte to identify what sensor was transmitting data 2 bytes of data 2 byte footer
Conclusions The mavrk system is a modular and versatile development platform that can be used for swift prototyping. The sparkfun weather station is straight forward and well documented Code Composer is an easy to use and friendly environment.