Simple Light Switch

Light switch is a simple circuit that can be used to control the LEDs based on surrounding light. Sensors used to detect the light on this circuit using LDR Light Switches. This circuit uses only three transistors and a few supporting components. As a contactor for Light Switches lamp circuit uses relay. To set the sensitivity of the exposure can be adjusted by adjusting R7. Light Switches circuit uses a source of DC voltage 9-12 Volt. For more details can be viewed directly from the following series of images.

Light Switches Series

Component List:

R LDR

R1 4.7 K

R2 1.2 K

R3 2.2 K

R4 1.2 K

R5 1.2 K

R6 2.7 K

R7 100 K

C1 10 uF/16V

TR1 BC107-BC108

TR2 BC107-BC108

TR3 BC557-BC558

D1 1N4148

RELAY 12V

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Automatic light activated switch circuit

The circuit can be used for switching OFF a particular lamp or group of lamps in response to the varying ambient light levels. The unit once built can be used for switching OFF a lamp when dawn breaks and switching it ON when dusk sets in. The power supply is a standard transformer, bridge, capacitor network, which supplies a clean DC to the circuit for executing the proposed actions.

Automatic light activated switch circuit schematic

The LDR must be placed outside the box, meaning its sensing surface should be exposed toward the ambient area from where the light level is required to be sensed. The circuit can be used as an automatic street light controller system or a simple light activated switch.

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Miniature Strobe Light

Strobe lights are widely used by disco lovers to create wonderful visual effects in disco halls and auditoria. The circuit of a battery operated portable miniature strobe light, which can be constructed using readily available inexpensive components, is described here. For convenience and simplicity, an ordinary neon lamp is used here in place of the conventional Xenon tube. The whole gadget can thus be easily accommodated in a small cabinet, such as a mains adaptor cover, with a suitable reflector for neon lamp to give a proper look. Since current requirement of this circuit is very small, it may be powered by two medium-size dry cells (3V) or Ni-Cd cells (2.4V). Transistors T1 and T2 in the circuit form a complimentary-pair amplifier. When switch S1 is momentarily depressed, the circuit oscillates because of the positive feedback provided via resistor R2 and capacitor C1 to the base of transistor T1. The sharp pulses in the secondary winding induce a high voltage in primary winding of transformer X1, which in fact is a line driver transformer (used in reverse) which is generally used in 36cm TV sets. High voltage pulses induced in primary side are rectified by diode D1 and rapidly charge reservoir capacitor C2 to nearly 300V DC. When switch S1 is released, capacitor C2 holds the voltage level for a finite period while capacitor C3 charges slowly through resistor R3. When voltage across capacitor C3 becomes high enough, neon strikes and the capacitor rapidly discharges through the lamp. When voltage across capacitor C3 falls below the extinguishing potential of neon lamp, it goes off and capacitor C3 starts charging again. This cycle keeps on repeating for a short time, based on the reservoir capacitor C2’s value. Precautions. The neon lamp flasher section of this circuit carries dangerously high voltages. All precautions should therefore be taken for protection. Before any repair work, discharge capacitor C2 using a short length of wire with a 100k resistor connected in series.

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Interior Light Fader for Automobile

Here the schema diagram of Interior Light Fader for Automobile. The schema is build using low power operational amplifier LM324 which only need around 3mA of current, so it wont bother the battery supply if left connected for extended periods. This schema is similar to the fading eyes schema above and is used to slowly brighten and fade interior lights of older cars.

The top two op-amps schema module (pins 1,2,3 and 5,6,7) form a triangle wave oscillator running at about 700Hz while the lower op-amp (pins 8,9,10) produces a linear, 5 second ramp, that moves up or down depending on the position of the door switch. The two transistors and associated resistors serve to limit the ramp voltage to slightly more and less than the upper and lower limits of the triangle waveform. These two signals (700 hZ. triangle wave and 5 second ramp) are applied to the inputs of the 4th op-amp (pins 12,13,14) that serves as a voltage comparator and produce a varying duty cycle square wave that controls the IRFZ44 MOSFET and lamp brightness. The 5 second fade time can be adjusted with the 75K resistor connected to the door switch. A larger value will increase the time and a smaller value will speed it up.

When the door switch is closed (car door open) the voltage on pin 8 slowly increase above the negative peaks of the triangle wave producing a short duty cycle output and a dim light. As the ramp moves farther positive, a greater percentage of the triangle wave will be lower than the ramp voltage producing a wider pulse and brighter light. This process continues until the ramp is 100% above the positive peaks of the triangle wave and the output is maximum. When the door switch is open, the reverse action takes place and the lamps slowly fade out.

The MOSFET IRFZ44 shouldnt need a heatsink if the total load is 50 watts or less but the temperature of the MOSFET should be monitored to make sure it doesnt overheat. The on-state resistance is only 0.028 ohms so that 4A of current (48 watts) is only around 100mW. For larger loads, a compact heatsink can be added to keep the MOSFET cool. - Interior Light Fader for Automobile schema diagram

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