Circuit detectors and sensors based electronics projects

This temperature switching circuit is designed to monitor temperature using a sensor manufactured by National Semiconductor LM335, which provides an output voltage of 10 mV / ° C. This voltage is compared to IC1a and IC1b two reference voltages. One of them is fixed and the other with P2 to P1. Comparator output is used for switching of D2, D3 and D5.
Note that this temperature switching circuit is designed for temperature monitoring "normal" between 25 and 100 ° C.

Using electronic diagram below can be made a very simple circuit that activate a relay at the touch of a sensor with finger.

This touch switch electronic circuit is based on a Schmitt trigger with latching, built IC1a, IC1b and R3. IC1b's output signal comes back to IC1a input through R3, resulting in maintaining stable condition of both gates. While the circuit is at rest, the anode of D1 is at "0" and the cathode of D2 is at level "1" retain their status.
When contact is shorted by finger touch, the voltage drop across R8 increases. This increase is translated into a short pulse of R1-C1. This pulse transmit through D1 a “ 1” at input of ICla. IC1b's output and output will also go to "1".