Super Light Sensor

Posted on Feb 7, 2014

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 the leaves of a tree. At the same time, i

Super Light Sensor
Click here to download the full size of the above Circuit.

t has a high level of rejection of natural light variations, such as sunrise, sunset and the movement of clouds. While it is a "passive" system, it can also be used as an "active" system - ie, used in conjunction with a light beam. Its great advantage here is that, since it responds to fluctuations in light level rather than the crossing of a specific light threshold, it is much more flexible than other typical "active" systems. It can be placed within the line-of-sight of almost any light source, including "vague" ambient light, and simply switched on. As shown, the LDR is wired as part of a voltage divider so that, between darkness and full sunlight, its output at "X" varies between about one-quarter and three-quarters of the supply voltage. A wide variety of sensors may be used in place of the LDR, including photo-transistors, photo-diodes and infrared and ultraviolet devices. Fig. 1: light level fluctuations are detected by LDR1 and the resulting signal fed to comparator stage IC1. IC1 in turn triggers 7555 timer IC2 which is wired as a monostable and this drives transistor Q2 and a relay. The signal from the sensor is fed to the inputs of comparator IC1 via two 150kO resistors. However, any signal fluctuations will be slightly delayed on pin 3 compared to pin 2, due to the 220nF capacitor. As a result, the pin 6 output of the comparator (IC1) switches low during short-term signal fluctuations and this triggers...

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    Ttl logic tester
    Twin Bell Circuit Circuit
    Arduino Midi
    Telephony Circuits and DTMF Circuits
    lm3914 in dot mode
    cellphone operated land rover connection to mobile phone problematic
    TTL Three - State Logic Probe PCB
    H Bridge tutorial
    UHF Indicator - Wavemeter
    Voltage Multiplier for Power LED Driver
    Raspberry Pi Driving a Relay using GPIO