By Phil Ray electron@ieee.org 3-Nov 1999

INTRODUCTION HARDWARE SOFTWARE OPERATION IMPROVEMENTS

INTRODUCTION

This simple circuit is designed to report the temperature via any standard FM broadcast band radio at regular intervals. It uses a simple low bit rate tone signalling scheme which can be interpreted easily by both humans and machines. Such a device can be used stand-alone or as part of a PC-based weather station or HVAC system.

My prototype was constructed with an ATMEL AT90S1200 fitted to a Dontronics SimmStick model DT-104. To save design time, I modified a low cost "wireless microphone" kit to act as the transmitter.

Commercial wireless thermometers are usually sold with only one receiver/display unit, and thus are limited to monitoring at only one location. My design allows any inexpensive FM radio to be used to monitor the temperature. Any number of monitoring locations can easily be set up.

Also, by plugging the output of the FM radio into the sound card on a PC and running a program which I am developing, temperature data can be logged for later display/analysis.

A prototype version built into a Sescom LAB-9 enclosure. The "TUNING" control is a small screwdriver adjustment between the 2 screws in the photo. Operation in harsher environments would require a weatherproof enclosure.

Inside the box, the guts of the system are 2 PCBs, the DT-104 and a modified "wireless microphone" kit.