Electronic projects


you are here: home page :: projects :: Sensors & control :: light controlled :: Simple optical switch

Simple optical switch

Circuit diagram

Introduction
The 555 is proved to be the most versatile and ubiquitous IC all over the world.This is a possible use: simple inverting schmitt trigger.

Circuit explanation
When the phototransistor is stroken by IR light it conducts and the voltage between the 1Mohm resistor(arbitrary) and the phototrans drops from VCC to lower values. When the voltage drops lower than VCC/3 the 555 is triggered and goes high (from 0 TO VCC). The amount of light that strike the phototrans necessary to bring his collector to VCC/3 is determined by the resistor (Vdrop = Icollector * R , so , if Vdrop= 2*VCC/3, the resistance needed to set the threshold on current is R=2*VCC/(Icollector*3)). High sensibility phototrans would need a smaller resistor, and weaker phototransistors higher value resistor, you can also use a trimmer to set the on threshold level with precision. The time of phototransistor isn't critical. The 555 has high current capability and can drive various devices, such as Bipolars, relays, bipolars+relays, mosfets, mosfets + totem pole , or give a logic output (see pic).
In case you need to trigger something when the gate is blocked (for example a burglar alarm, or a multistage coilgun) you need to invert the output, which is accomplished using a small bipolar transistor wired in an inverting setup (see pic) or swapping the positions of phototransistor with the resistor, so the voltage will drop under VCC/3 when blocked: The formula to determine the resistance to turn off at Icollector is R=VCC/(Icollector*3).

Have fun!

author: Jonathan Filippi
e-mail: jonathan.filippi@virgilio.it
web site: http://www.electronics-lab.com
project categories:
folder Audio (49)
folder Power & high voltage (43)
folder Radio (23)
folder Light & LED (31)
folder Tools & measurement (40)
folder Telephone (18)
folder Automotive (10)
folder Microcontrollers (12)
folder Sensors & control (47)
folder Timers & oscillators (40)
folder Miscellaneous (26)

StumbleUpon button

Share this page
Bookmark and Share
project subcategories:
All subcategories
light controlled
temperature controlled
moisture controlled
sound controlled
other

similar projects:
Infa-Red Remote Control
Infra Red Remote Control Extender
Infra Red Switch
Infra-red Level Detector
Infrared Detector
Infrared gate 2
Infrared Remote Control
IR Remote Control Extender Circuit
Light switch
Light/Dark Detector

recently added projects:
Doorbell for the Deaf
High Quality Intercom
Combinational Conjuring Trick
POT-PLANT POWER
Ultrasonic Dog Whistle
Quiz Circuit
LED Torch
Insect Repellant
Speaker Microphone Circuit
Magic Wand Conjuring Trick.

most popular projects:
Led display digital Voltmeter
500W low cost 12V to 220V inverter
Low pass filter - Subwoofer
Metal Detector
High And Low Voltage Cut Off With Time Delay
Basic UPS Power Supply
2N3055 Power Amplifier
200W audio amplifier
LED Torch
100W RMS Amplifier


DIY Electronics Projects

Promote Your Page Too