Light-sensitive Alarm Project

The circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms. The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light is arranged to fall on the light-sensor. Breaking this beam will then cause the bleeper to sound. The light sensor is an LDR (light-dependant resistor), this has a low resistance in bright light and a high resistance in dim light.

• The light-sensitivity of the circuit can be adjusted by varying the 100k preset.
• The length of bleep can be varied from 0.5 to 10 seconds using the 1M preset.

Using the 7555 low-power timer ensures that the circuit draws very little current (about 0.5mA) except for the short times when the bleeper is sounding (this uses about 7mA). If the circuit is switched on continuously an alkaline PP3 9V battery should last about a month, but for longer life (about 6 months) you can use a pack of 6 AA alkaline batteries.

This project uses an edge-triggered 555 monostable circuit.

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Parts Required

• resistors: 10k, 47k, 1M ×3
• presets: 100k, 1M
• capacitors: 0.01µF, 0.1µF, 10µF 25V radial
• transistor: BC108 (or equivalent)
• 7555 low-power timer IC
• 8-pin DIL socket for IC
• LDR (light-dependant resistor) type ORP12
• bleeper 9-12V
• on/off switch
• battery clip for 9V PP3
• stripboard 12 rows × 25 holes

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Stripboard Layout

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Circuit diagram

Model Railway Level Crossing Lights

A magnet under the train operates reed switches positioned on the track. The trigger reed switch starts the sequence by switching on the amber light, a few seconds later the two red lights start to flash. When the train has passed the level crossing it operates the cancel reed switch which switches off the lights until the next train arrives.

There is a PCB pattern for this project, but if you don't have facilities to make PCBs you can build this project on stripboard instead. Please see the New Railway Modellers website for a stripboard layout and advice on making model lamps and barriers.

This project uses a 555 monostable circuit to switch on the amber LED for a few seconds. When this switches off it triggers a 555 bistable circuit which switches on a 555 astable circuit to flash the red LEDs.

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Parts Required

• resistors: 680 ×3, 1k ×3, 33k, 47k, 82k, 270k
• capacitors: 0.1µF ×3, 10µF radial ×2
• red LED (3mm best) ×2
• amber* (or yellow) LED (3mm best)
  * some amber LEDs are too orange to look correct, yellow may be better
• 555 timer IC ×3
• 8-pin DIL socket for IC ×3
• on/off switch
• battery clip
• reed switch ×2
• miniature magnet - each locomotive needs one
• printed circuit board (PCB) - pattern given below

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PCB component layout

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Track connections

The reed switches can be held in place between the rails with a small piece of blu tac.
Each locomotive will need a miniature magnet glued to its underside, test first with blu tac, then use superglue.

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Circuit diagram

Circuits: 555 monostable (on left) | 555 bistable (in middle) | 555 astable (on right)

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PCB copper track pattern

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Stripboard layout

If you don't have facilities to make your own PCB you can build this project on stripboard. Please see the New Railway Modellers website for a stripboard layout as well as advice on making model lamps and barriers

Electronics Projects – Mini Projects and Final Year Projects

Following are mini project ideas for Electronics Engineering students:

• Home Automation (Ac/Dc) Using Pc Interface
• Color Reflectance Measurement (Solids)
• Access Control System
• Infrared Toy Car Motor Controller
• Dc Motor Direction Control
• Logic Analyzer
• Line Telephone Share
• Simple Code Lock

• Leaf Moisture Analyzer
• Industrial Automation Data Acquisition System
• Variable Auxiliary Power Supply
• Microcontroller based Scrolling Message Display
• Ultra Bright LED Lamp
• DTMF Development Board
• Mobile Cell Phone Charger
• Data Logger
• Solar Battery Charger And Shunt Regulator
• Automatic Light Lamp with Morning Alarm
• G.P.S. Receiver
• FM Booster
• LED Panel Meter
• Air Flow Sensor
• 7 Digit Code Lock (6 – 15v)
• Light Sensitive Inductive Load Controller
• Robot Control Using TV Remote
• FET 4 Input Mixer (+/-9v)
• Quality FM Transmitter
• Autonomous Robot
• Classic Ac 230 V Timer
• Infrared Control For Pc
• Altimeter — To Measure The Altitude
• Build A Simple Infrared Illuminator
• Fire & Smoke Alarm System
• House security system
• Electronic security system
• Clap Switch
• Stepper Motor Control Using Microcontroller
• 4 Digit 7-Segment Multiplex DISPLAY
• Infrared Auto Switch
• Digital Alarm Clock
• Light Sensing Robot
• Ionizer Mains (230v Ac)
• Dc Motor Control PWM Technique
• Telephone Number Display
• DTMF Proximity Detector
• U.S.B. Connectivity To Micro Controller
• Automatic Control for Unmanned Railway Gate.
• Telephone Receiver
• Solar Lighting System
• Build A Carbon Monoxide SNIFFER
• Liquid Dispensing System with Touchscreen
• Temperature Controlled Soldering Station
• Microcontroller Based Intelligent Glass Break Detector
• Telephone Call Counter
• Electronic watchdog
• Automated Traffic Signal Controller
• Fastest Finger First Indicator
• DTMF Telephone Remote Control
• Line Follower Robot
• Automated Car Parking System
• Depth Of The Medium Based On Attenuated Reflectance
• Dual Motor L298 H-Bridge Control
• Micro Controller To Ethernet Interface
• Baby Incubator
• Interfacing IBM Key Board To Micro Controller
• Intelligent Battery Charger
• UNIPOLAR 4-Phase Stepper Motor Controller Board
• Condenser Mice Audio Amplifier
• Electronic Eye With Security System
• Who’s First (Game) Indicator
• Auto turn off battery charger
• Micro Controller Clock
• L293 H-Bridge Dc Motor Controller
• Invisible Broken Wire Detector
• Wireless Vehicle Path Tracer Using IR & RF
• Electrical Equipment Controller
• Simple Function Generator 12v
• Musical Touch Bell
• Electronic Jam
• Anti Theft Alarm For Bikes
• IR Remote Switch