Music test light circuit

Ordinary electric pens use neon tube displays, which are difficult to observe and distinguish in strong light environments. In addition to using LED displays, the music test pen can also emit musical
sounds to distinguish whether there is power or not. Moreover, hidden wires can be easily found in the walls of rooms with concealed wires. '.
    Figure l6-35a is the circuit schematic diagram of the music electroscope. The detection circuit is composed of field effect transistor VT1 and transistor VT2. When there is electricity,
the alternating magnetic field generated by the mains generates an induced potential in the detection circuit, causing the on field effect transistor VT1 to turn off. VT2 is turned on, the light-emitting
diode LED lights up, and the music card circuit plays the sound. No power pair. VT1 is turned on, and V product is less than 0.7V, causing VT2 to be turned off.
    The field effect transistor VT1 of the music electroscope uses an N-channel junction field effect transistor 3DJ6, and the transistor VT2 uses a silicon NPN
low-frequency transistor 3 DX201B, with an amplification factor greater than 100. The music card circuit can use an ordinary music greeting card circuit. Light-emitting diodes
should be imported tubes that are usually transparent and emit red light after being powered on to facilitate comparison in strong light environments. Laminated battery for power supply crystal radio
4F22 type 6V. Resistors and capacitors are small components. The shell can be replaced by a commercially available remote control shell. The reference size is 120mm×
36mmX 25mm.
    The picture is the printed circuit board diagram of the music electroscope pen. The size of the printed circuit board is 32mm×32mn. The induction coil of the music electroscope pen is made of
a plastic copper wire with a diameter of 1.13mm to make a small circle with an inner diameter of 3mm, and is soldered to the printed circuit. On the board, keep the sensor away from the power line. Turn on the power switch and adjust
the resistance of resistor R2 to make transistor VT2 just cut off. Then put the induction coil close to the phase line, due to the effect of the electric field. VT1 is cut off, VT2 is turned on, and
the light-emitting diode lights up. Decrease the resistance R from large to large, so that the voltage at both ends of the music card is between 2-3V. The music card circuit works and drives the piezoelectric ceramic piece
to make sound. If you stick the pen on the wall and move it slowly, you can use the light-emitting diode LED and the sound of music to determine whether there are hidden live
wires in the wall. This can avoid the risk of electric shock when drilling holes in the wall. At the same time, you can also find the in-line breaks in live wires.