An temperature indicator electronic circuit can be designed using electronic diagram below. Temperature circuit uses only the following three integrated circuits, a temperature sensor LM335, LM723 voltage regulator and a level detector with five analog outputs, TL489.
Temperature sensor (IC1) is supplied with a steady stream of reference to the output of LM723 (IC2). This ensures a stable zero point allowing the claim is very accurate. Parts around 723 are thus chosen to allow the regulator output to vary between zero volts and a volt.
A very simple light sensitive switch circuit that can be used in applications like scale automatically lighting, automatically opening a door under the action of a beam of light can be built using electronic scheme from the figure below.
A smoke detector electronic project can be designed using electronic diagram below. Smoke detector circuit diagram below does not use ionization detection, gas or optocouplers it use two photoresistors (LDR's) and an LED.
Smoke detector is built using LM1801 chip which facilitates building using a minimum of components.
Diode D1 rectifies voltage, R7 reducing voltage at a level suitable for integrated circuit.