Bass Sensitive Light Circuit

Bass sensitive lights are lighting units which react to the bass of music and flash to the beats. They are great for professional or private use at parties and events . A bass sensitive light or bass activated light has a built-in microphone which will pick up and respond to sound. These lights are a great way to add a touch of class and create the perfect party atmosphere with minimal effort. They can however cost a lot; although you can pick up cheap ones with a few LEDs for ~£100. If you are a hobbyist, engineer or just a keen DIYer, you can easily and cheaply put together a bass sensitive light circuit using general purpose electronic components and an LED strip.
LED strip lights

The topology for a simple system is as follows in that order: A microphone, a preamplifier, a low pass filter and the LEDs driver. The preamplifier and the low pass filter can be built with a general operational amplifier such as the 741.

The circuit shown in this post works as follows:
1. The microphone detects the music and is fed to the preamplifier.
2. The preamplifier amplifies the signal and the output is fed to the low pass filter.
3. The low pass filter only allows the low frequency components of the music to go through. (As in the bass)
4. The filter output is fed to the comparator and is compared to a predefined DC level.
5. The output to the comparator toggles to high when the filter output signal exceeds the predefined DC level.
5. When the output of the comparator is connected to the base of an NPN transistor.
6. When the comparator output is high, the NPN BJT is turned on allowing current to flow through a series of LEDs.

Bass Sensitive Light Circuit Schematic

The schematics for the bass sensitive light is shown below. The preamplifier and the filter circuit uses the 741 opamp. A 100k potentiometer is present in the first stage feedback and is used to adjust the gain. The filter stage also have further gain amplification and can be adjusted with a pot. The bandwidth of the filter is adjusted with the 10 k pot. C2 is 1uF.

The comparator circuit is built using LM311 and a 10 k pot is used to adjust the DC level. The output of the LM311 drives the base of a ZTX653 BJT.
Bass Sensitive Light Circuit Schematic

The whole circuit is powered with two PP3 9V batteries providing -/+9V. The output stage for driving the LEDs is powered by 12V. We used an old computer power supply to get the +12V and we bought a meter of LED strip for £1.84 from eBay.

The gain of the first stage and the second stage needs to be adjusted during operation; if the music is too loud, the amplifier stage will saturate and the gain will need to be reduced by turn down the value of the pots.


Bass Sensitive circuit
The circuit was connected up and a cheapish microphone was plugged to the input and we played some music. We measured the signal received at each stage of the circuit on an oscilloscope:
Preamplifier Waveform

This signal is then fed through the low pass filter circuit to give:
Filtered Waveform
The filtered signal goes to the comparator and the comparator output goes high when the signal exceeds the predefined DC level.
Comparator Output

The DC level will determine how much of the signal will toggle the LED on. If the DC level is too low, the LEDs will always stay on as all the music signal will be higher than that predefined DC threshold level. Watch a demo of the circuit here:

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