#653 USB Audio Level Indicator Kit
An electret-input audio level kit based on cascading LM358 stages with LED indicators.
Here’s a quick demo..
PS: Samba do Cajón - Abellán Oficial
Notes
This 20-LED audio volume indicator kit is widely available from sellers on aliexpress - mine came from WAVGAT Official Store.
It is USB powered, and uses an electret microphone for sound input.
It produces a very nice symmetrical display, pumping out to right and left as the volume increases.
Kit Specifications
Voltage: 5-12V LED: 12 green, 8 red Board size: 160mm x 18.5mm
Parts List
| Item | Qty | Ref |
|---|---|---|
| 2kΩ | 1 | R28 |
| 1kΩ | 1 | R24 |
| 510Ω | 11 | R26,27,22,21,18,17,14,13,9,10,5 |
| 5.1kΩ | 3 | R6,4,2 |
| 100Ω | 4 | R11,12,7,8 |
| 1N5819 | 1 | D23 |
| 1MΩ | 1 | R3 |
| 500kΩ trimmer | 1 | RP1 |
| 1N4148 | 2 | D1,22 |
| 430Ω | 2 | R23,22 |
| 200Ω | 3 | R19,16,15 |
| 10kΩ | 2 | R25,1 |
| 104, 100nF | 2 | C1,3 |
| 5mm Red LED | 8 | D14-21 |
| 5mm Green LED | 12 | D2-13 |
| LM358 | 6 | U1-6 |
| DIP8 socket | 6 | U1-6 |
| electret mic | 1 | MIC1 |
| 100µF electrolytic | 1 | C2 |
| 4.7µF electrolytic | 1 | C4 |
| micro USB socket | 1 | K1 |
Circuit Design
Here’s my redrawing of the circuit using Fritzing, so any errors are mine. Layed out this way, the circuit behaviour is easily apparent. A quick summary:
- the electret mic is based with a conventional input circuit wit the AC signal offset and fed to LM358 (U1a) op-amp, configured as a non-inverting amplifier with the amplification (sensitivity) set with RP1
- LM358 (U1b) buffers the signal and outputs the “audio reference signal”
- the audio reference signal is fed to 10 op-amp units used as comparators against 10 discrete voltage levels
- the 10 discrete voltage levels are set with a multi-stage voltage divider
- each op-amp output drives two LEDs (left and right)
The circuit is actually the basis of the LM3915 that I covered in #065 LevelIndicatorLM3915 and #202 Audio Level Indicator Kit. Note that the resistors are not identical on the LM3915, but form a logarithmic scale. If a linear scale is needed, there is the LM3914 that is otherwise identical. Linear scale is usually better for voltage control of batteries, and logarithmic one for audio level.
Construction complete:
Next Step
The unit works very well, even on 4.5V (3xAA). I’m thinking of making a case for it next with option of battery or USB power.
Credits and References
- USB audio spectrum lamp kit LED car volume level indicator music audio display circuit board to increase the hands-on ability - kit from aliexpress seller WAVGAT Official Store
- LM358N Datasheet
- 1N4148 Datasheet
- 1N5819 Datasheet