Temperature regulator

My first project was this  schematic to measure and control temperatures.


The temperature is measured by the sensor LM35C, this is a calibrated sensor with an accuracy of 0.25 degree per degree. The sensor has an output of 10 mV/C.

The regulation  consists of the LM324, it is used as a comparator with a hysteresis of 0.5 C. The temperature setting is via the potentiometer of 10K. Using the resistance Rx of 18K it is possible to measure temperatures below zero, see lm35c.pdf.

The temperature reading and settings are done by the CMOS analog switches IC5 and IC6. The switches in these ICs are sequentially controlled by the timers and dividers IC 1.2 and 9. It is also possible to  secure the  readout  with S2, wiith S3 can be used to selected the next readout. S2 is used to select the settings.