PROJECT: SMS thermometer

General description:

A thermometer with a modem. Can be used to monitor room temperature remotely e.g. to prevent freezing of water pipes.


General description:

PN-junction threshold voltage's temperature dependency is used for measurement. A constant current is generated by an op-amp. Another op-amp amplifies the voltage and offsets the output voltage suitable for a PIC 16F690 microcontroller analog input. PIC communicates with Adafruit's SIM800- module using AT-commands through UART. An inquiry can be sent by a cell phone to the module which responds by sending back the measured temperature in an SMS. Indicator leds on the top cover show roughly the temperature, <0, 0-5, 5-10, 10-15, 15-20, or >20 degrees C.



Adafruit Industries SIM800- module

PIC 16F690





Schematic controller

Schematic SIM module

PCB controller