Abstract:

The Touch Switch with Lamp circuit is based on a readily available touch sensor, comparator IC LM393, and relay. The touch sensor acts as the touch detector, while the IC LM393 functions as a comparator. In the absence of touch, the touch sensor remains non-conductive, and the LED stays off. When touch is sensed, the touch sensor becomes conductive, and the LED glows.

Application of the Circuit:
Traditional touch sensor-based circuits often use costly and complex components. However, this Touch Switch with Lamp circuit leverages a readily available touch sensor, reducing cost and simplifying the circuitry. The circuit automatically activates the LED in the presence of touch, providing a continuous glow, signaling touch detection.

Why This Circuit:
The touch sensor is easily modifiable by simply touching it with a finger. Operating over a DC voltage of 5V (via a DC supply cable), this circuit is efficient and straightforward for various applications.

Explained Working of the Circuit:
The core idea is to turn ON the LED when a touch is detected. The touch sensor converts touch into electrical energy, while the IC LM393 functions as a comparator. The relay acts as a switch—normally closed contact becomes open, and normally open contact becomes closed. The LED remains off when no touch is detected but glows when touch is sensed.

How to Build:
Carefully study the manual, circuit, PCB layout, and components before soldering. Use color-coded resistors and ensure correct component placement, particularly paying attention to polarity-dependent components like diodes and electrolytic capacitors.

Testing the Kit:
After assembly, connect a 5V DC power source. Manually touch the sensor; the LED will glow if working correctly. Adjust the R2 variable resistor to set the desired light intensity.

ICs Used:
LM393 – A dual differential comparator IC, widely used and popular.

Part List:

• Semiconductors:
  U1 – LM393 (8-pin comparator)
• Resistors:
  R2 – 10k Ohm (variable)
  R3 – 1k Ohm
  R4 – 1k Ohm
  R5 – 10k Ohm
  R6 – 10k Ohm
• Capacitor:
  C1 – 1uF
• Miscellaneous:
  D4 – Touch sensor
  D1 – Red LED
  D2 – Green LED
  5V USB Cable
  PCB
  LED
  Relay

Key Applications:

Used widely in electronic circuits, automation, robotics, and educational projects. Optimized for reliable performance in India-specific environments and conditions.

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