Circuits.
The circuit comprises signal amplifier and analogue display circuits. Voltage variation from the sensing pads are amplified by the transistor BC548(T1), which is configured as a common-emitter amplifier.The base of T1 is connected to one of the touch pads through resistor R1 and to the ground through potmeter VR1. By varying VR1, the sensitivity of T1 can be adjusted to the desired level. Diode D1 maintains proper biasing of T1 and capacitor C1 keeps the voltage from the emitter of T1 steady.
The amplified signal from transistor T1 is given to input of IC LM3915(IC1) through VR2. IC LM3915 is a monolithic IC that senses the analogue voltage levels at its pin 5 and display them through LEDs providing a logarithmic analogue display.
The circuit comprises signal amplifier and analogue display circuits. Voltage variation from the sensing pads are amplified by the transistor BC548(T1), which is configured as a common-emitter amplifier.The base of T1 is connected to one of the touch pads through resistor R1 and to the ground through potmeter VR1. By varying VR1, the sensitivity of T1 can be adjusted to the desired level. Diode D1 maintains proper biasing of T1 and capacitor C1 keeps the voltage from the emitter of T1 steady.
The amplified signal from transistor T1 is given to input of IC LM3915(IC1) through VR2. IC LM3915 is a monolithic IC that senses the analogue voltage levels at its pin 5 and display them through LEDs providing a logarithmic analogue display.
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