The circuit mainly consists of the condenser microphone, the transistor amplifier and the light emitting diodes.
At stable state, VT1 in a critical saturation point, so that VT2 deadline, LED1 and LED2 neither LED, R1 to the capacitor microphone MIC to provide bias current, seized the microphone in the indoor environment after the acoustic signal to a corresponding electrical signal by capacitance C1 to VT1 to enlarge the base, VT1, VT2 composed of two direct-coupled amplifier circuit, as long as the right to select R2, R3 to make a silent-wave signal.
VT1 in a critical saturation point, and to enable VT in a closed state, two LED no current flow through without LED, when the acoustic signal MIC seizure, there is audio signal into the base of the VT1, the signal so that the negative half-cycle VT1 from the saturation, VT1 rise of collector voltage.
VT2 conduction, LED1 and LED2 LED light, when the input audio signal when a weak, not enough to withdraw from the VT1 saturation, LED1 and LED2 remain extinguished, and only when a strong signal input to light-emitting LED was lit, Therefore, LED1 and LED2 will sound as the environment (such as music, speech) signal strength of ups and downs and flashing LED.
Components List:
| VT1 - 9014 |
VT2 - 9014 |
BT200- Microphone
|
C1 - 1uF/16V |
| R1 - 4.7K |
R2 - 1M |
R3 - 10K |
C2 - 100uF/10V |
LED assembly and debugging:
1. According to the principle of the assembly drawing pictures, and then assembled by the assembly.
2. The attention of the transistor can not take the wrong polarity, components neatly arranged, beautiful.
3. Electricity VT after the first test of the collector voltage to between 0.2 ~ 0.4, if the voltage is too low to exert the voice signal, VT1 can not withdraw from the saturation point, VT2 conduction can not be, if the voltage exceeds the VT2 dead-zone voltage, when the static on the on-VT2 to LED1 and LED2 LED light, so.Capacitance for different microphone sensitivity, and β values of different transistor, VT1 of the size of the collector resistor R3 to determine through testing.
4. From about 0.5 meters away from the microphone, the voice of the ordinary (moderate volume) speech, LED1, LED2 should be with the scintillation voice.
For loud, the only flashing light-emitting LED, can be appropriate to reduce the resistance value R3 can also be a greater value of the replacement transistor &beta.