#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..
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.
Voltage: 5-12V LED: 12 green, 8 red Board size: 160mm x 18.5mm
|5mm Red LED||8||D14-21|
|5mm Green LED||12||D2-13|
|micro USB socket||1||K1|
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.
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