RS-232 Powered Temperature Sensor

This is a simple circuit that shows the interface of a temperature transducer through a RS-232 interface cable. It can be used to measure a remote temperature far from the host system. While drawing little supply current from the power source, the temperature is converted into a square wave with a frequency proportional to the absolute temperature of its package by the temperature sensor. This circuit uses RS-232 interface to provide power to the sensor because the amplitude of the output signal must be sent over a cable to the host system and it is equal to the power supply. Here is the circuit :

As the temperature sensor, this circuit uses MAX6577. One driver output of a 3V-powered RS-232 transmitter IC2 delivers the power supply to the MAX6577. The IC’s driver delivers a minimal current to the receiver at the end of the line, but it can regulate the output voltage up to ±5.5V. To prevent reverse voltages and helps lower the IC1 supply voltage to +5V this circuit uses diode D1.  We must ensure that input of one receiver inside IC2 and IC1 output voltage levels are compatible between them, to guarantee a safe communication. [Source: maxim-ic.com]