The circuit is mainly composed by Power Circuit, Audio Amplifier Circuit, Frequency Dividing Circuit and LED Driver Circuit.1,Power Circuit: The power output voltage is 9V--15V. D1 can avoid the demage of three terminal regulator when the power polarity is connected in a wrong way. After the C4's filtering , L7806 three terminal regulator will provide the whole circuit with a stable voltage of 6V. 2,Audio Amplifier Circuit: Electret microphone MK1 transfers the obtained sound to electric signal which will be amplifed twice by Q1 and Q2. At this time, UR1 can adjust the size of Q2 signal in order to adjust the sensitivity of the whole circuit. 3,Frequency Dividing Circuit: Three frequency dividing circuits is added to indicate the electrical level on the different frequency, as it's featured with three sections of LED indicator in a seperate way. VR2, VR3 and VR4 are used for adjusting the sensitivity of LED indicator on the different frequency. The sound signal from three different frequency can be distinguished according to the different capability of C6, C10 and C11. Q4, Q5 and Q18 collectors can obtain three different frequency and the voltages after dividing and amplifying by diode and transistor. The level of voltage depends on the size of the sound from outside. 4,LED Driver Circuit: There are 9 pieces of 1N4148 diode in each frequency. If the sound is louder, the higher voltage will be obtained by Q4,Q5 and Q18 connector and more 1N4148 start work. Then more LEDs can light. Three-segment 10-point voice-activated level indicator kit (blue, green, red 5mm high-brightness LED), including more than 200 components and 443 solder joints, is a relatively challenging soldering kit. Note: This is a DIY kit, and you need to solder it yourself. Colour:Random Color Material:PCB+components note:PCB board color is random, no specified color is accepted It's DIY kits, needs to finish by yourself. Package Contents: 1 * PCB board 1 * DIY kit Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.