This is a circuit that transmits temperature data over an IR link and it allows the isolation of temperature sensor. It is a good solution of obtaining temperature readings from points at potentials a few tens of volts from ground by linking a temperature probe  only by an IR connection to the readout point. This circuit consist of a temperature sensor, an IR receiver, and an IR transmitter. Here is the circuit:

IR Linked Temperature Sensor circuit schematic

As the temperature sensor, this circuit uses the MAX6576 that will convert temperature into period. This sensor is connected to the IR transmitter. The IR transmitter is triggered to generate a short (about 10µs), high-intensity IR pulse by each positive-going transition of the square-wave output from the MAX8576. This circuit also uses a 74HC132, the three fourth gates are paralleled and used as the IR LED driver and the remaining one gate is used as a positive edge differentiator. This circuit powered by a CR3032 lithium battery.

The second circuit is a IR Receiver/Signal Processor that is used  to receive the IR light pulses generated by the temperature sensor. It will transform the IR light pulses into two types of output: analog and digital. The analog output is a DC voltage proportional to the IR signal period and the digital output is simply a standard logic pulse recovered from the IR signal. This circuit consist of four circuit blocks : the signal-recovery/timing generator, the linear ramp generator, the buffered sample-and-hold and  the amplifier/filter. [Source: maxim-ic.com]