Schematic Reference

A very simple light alarm schematic circuit project can be designed using some common electronic parts, as you can see in the circuit diagram bellow . This light alarm schematic circuit project will sound as soon as the drawer is opened and light falls on the Darlington phototransistor. The output alarm may be redesigned to activate a relay or triac. This simple light alarm schematic circuit project use a MAL12 LDR photoresistor as a sensor .

Light Alarm Schematic Circuit diagram

The 14011 quad , 2 input, NAND gate is wired up to oscillate when the input to it goes high, that is the BC557 transistor turns on after light is detected by the MAL12. The oscillating output from the 14011 turns the BC547 on and off , making the buzzer to sound. After the alarm has started and it is put back into dark conditions , alarm will continue to sound for about 3 - 5 seconds. This is due to the 1uF capacitor and 4M7 resistor which keep the input to the 14011 high .

The circuit is very simple and must be powered from a simple 9 volts DC power supply or a 9 volt battery .

This is a simple parking light switch. The idea is that you drive your car towards your garage. You shine your headlights at the sensor, which switches on an external light . If you dont have a garage the sensor can be placed on a wall or post, and the external light will illuminate the area while you park and leave your vehicle. The circuit also has manual on and off controls.

Parking Light Switch Circuit Diagram


Notes:
This is a very simple light switching circuit using a single transistor and relay to control an external mains powered light. Relay RLA is drawn with two changeover contacts, but a relay with two make contacts can also be used. The contacts MUST be rated at 240V AC and at least 3 Amp (or higher) to safely switch loads of up to 500 Watts. Once energized the relay latches through contacts RLA1 and the external lamp is switched via contact RLA2.

Setting Up:
Wait until darkness and shine your vehicles headlights at the ORP12 Photocell. Adjust the 100k potentiometer until the relay triggers. Turn off the headlights and press S2 to turn off the relay. The external light should go off. It may be necessary to place a plastic tube of about 1 inch in length so that only light emitted by a cars headlights reaches the photocell. This will prevent unwanted triggering.

The light can also be manually controlled by pressing S1 which will latch the circuit, and S2 will turn off the lamp again.

Electronic components are included in the category of light sensors is LDR, Photo Transistor, Photo Diode, Infrared Receiver. The function of the electronic component is to detect the intensity of light received by the component. The light sensor is often used in electronic equipment such as on television, light a light switch, light intensity measuring instrument.

Simple Sound-to-Light Converter Schematic Diagram

The circuits below light a 20 watt lamp when the contacts are touched and the skin resistance is about 2 Megs or less. The circuit on the left uses a power MOSFET which turns on when the voltage between the source and gate is around 6 volts. The gate of the MOSFET draws no current so the voltage on the gate will be half the supply voltage or 6 volts when the resistance across the touch contacts is equal to the fixed resistance (2 Megs) between the source and gate.

The circuit on the right uses three bipolar transistors to accomplish the same result with the touch contact referenced to the negative or ground end of the supply. Since the base of a bipolar transistor draws current and the current gain is usually less than 200, three transistors are needed to raise the microamp current level through the touch contacts to a couple amps needed by the light. For additional current, the lamp could be replaced with a 12 volt relay and diode across the coil.

Fire alarm can be made with a light sensor (LDR) as in the article with the title of Fire Alarm with this LDR sensor. Principles of fire detection Fire Alarm with LDR sensor is to detect the presence of smoke through the LDR. LDR in the series Fire Alarm does not stand alone in detecting a fire, but the LDR in the pair with the light shining on the LDR.

Hence, in the detected smoke from the fire then the intensity of light received by the LDR LDR decreases and eventually trigger an alarm system on a series of Fire Alarm with this LDR sensor. Part 2 that in the series of Fire Alarm with Sensor LDR are some of the sensors, tone generator, audio power.

Image Series Fire Alarm with Sensor LDR

Function Section of the Fire Alarm with Sensor LDR

Part of LDR and light sensor facing to fire smoke detection

Part trigger using transistors and regulators as a trigger tone generator 7805

Tone generator section with IC UM66

Power audio section uses an audio power IC TDA 2002 which is equipped with voleme control (R3)