Sensor Circuits


House Security System

Here is a low-cost, invisible laser circuit to protect your house from thieves or trespassers. A laser pointer torch, which is easily available in the market, can be used to operate this device. The block diagram of the unit shown in Fig. 1 depicts the overall arrangement for providing security to a house. A laser […]


Radiator Temperature Indicator

This radiator temperature indicator can be designed using electronic circuit diagram below. Temperature indicator consists of two special zener diode, D1 and D2, connected in series to ensure accuracy of 5.96 V Zener voltage at 25 ° C. As long as the radiator temperature does not exceed 50 ° C, thermal indicator will flash a […]


Pulse Rate Monitor

This simple circuit enables you to listen to your heartbeat, for instance, while you are exercising. The transducer used for detecting the pulse is an electret microphone, X1 in the diagram. The model used has two (polarized) terminals. As usual with this type of microphone, it functions via a series resistor, R1. The potential drop […]


Ultrasonic Distant Obstacle Detector

The first sensor a robot usually gets fitted with is an obstacle detector. It may take three different forms, depending on the type of obstacle you want to detect and also — indeed, above all — on the distance at which you want detection to take place. For close or very close obstacles, reflective IR […]


Home Made Metal Detector

This homemade metal detector circuit will help you find objects composed of materials with relatively high magnetic permeability. It is not suitable for buried coins discovery that is not sensitive enough but you can detect pirates treasures! The metal detector is powered by 2 × 9V batteries, each of it charges with 15mA. L1 detector […]


Electronic Gate Keeper

This circuit can do the job of a Gatekeeper and alerts you if someone passes through the gate. The alarm can be an AC bell or a Lamp. The alarm turns on for 1 minute and stops if the light barrier is restored again. Infrared rays are used as the light barrier to activate the […]


Super Light Sensor

This “Super Light Sensor” responds to minute fluctuations in light level, auto-adjusting over the range from about 200 lux up to 60,000 lux (ie, from a modestly lit room to direct sunlight). It has lots of potential uses – eg, detecting a car entering a driveway, a person moving in a room, or wind rustling […]


Infra-Red Proximity Detector

The detector is intended for the recognition of obstructions at distances of a few millimeters to a few centimeters. Similar detectors are used in the industry and health services, for instance, to open a water tap via a magnetic valve. The sensor, IC2, is a Type SFH900 optoisolator from Siemens or similar. A phase-locked loop […]


Earth Fault Indicator

The security of many electrical devices depends today on the availability of an earthed mains outlet. We should remember that these are connected to the frame or to the metal housing of the equipment and so it routes to the protective earth (PE) connections. In this setup, mains voltage, however small, will cause the differential […]


Fastest Finger First Indicator

Quiz-type game shows are increasingly becoming popular on television these days. In such games, fastest finger first indicators (FFFIs) are used to test the player’s reaction time. The player’s designated number is displayed with an audio alarm when the player presses his entry button. The circuit presented here determines as to which of the four […]