Dancing LEDs


Posted on Feb 7, 2014

The basic circuit illuminates up to ten LEDs in sequence, following the rhythm of music or speech picked-up by a small microphone. The expanded version can drive up to ten strips, formed by up to five LEDs each, at 9V supply. IC1A amplifies about 100 times the audio signal picked-up by the microphone and drives IC1B acting as peak-voltage detector


Dancing LEDs
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. Its output peaks are synchronous with the peaks of the input signal and clock IC2, a ring decade counter capable of driving up to ten LEDs in sequence. An additional circuit allows the driving of up to ten strips, made up by five LEDs each (max. ), at 9V supply. It is formed by a 10mA constant current source (Q1 & Q2) common to all LED strips and by a switching transistor (Q3), driving a strip obtained from 2 to 5 series-connected LEDs. Therefore one transistor and its Base resistor are required to drive each of the strips used. Adopting the additional circuit, only one item for R10, R11, Q1 and Q2 is required to drive up to ten LED strips. On the contrary, one item of R9 and Q3 is necessary to drive each of the strips you decided to use. For example: if you decided to use 5 LEDs, pin #15 of IC2 must be connected to pin #1; if you decided to use 8 LEDs, pin #15 of IC2 must be connected to pin #9 etc. Whishing to use a wall-plug adapter instead of a 9V battery, you can supply the circuit at 12V, allowing the use of up to 6 LEDs per strip, or at 15V, allowing the use of up to 7 LEDs per strip.




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