Here’s a circuit to display the songnumber in an audio system forquick reference to songs. It alsoserves the purpose of an extra visual indicatorin modern audio systems.When the power is switched on, thepower-on-reset circuit comprising 3.3kresistor R20 and 1μF, 25V capacitor C6resets the counters, showing ‘00’ in the display.One can also reset the display to zeroat any time by pressing reset switch S1.When the first song starts playing, theoutput pins of IC1 (KA2281) go low andcapacitor C5 starts charging. This forwardbiases transistor T1 and hence the inputto IC3 at pin 1 goes to high state. As aresult, the output of the counter goes tothe next state, showing 01 on the display.The counter remains in this state until thesong is completed.During the time gap before the next songstarts playing, capacitor C5 discharges. Afterdischarging of capacitor C5, the input to IC3becomes low again. When the song starts,the process described above is repeated andthe display shows 02. You can adjust VR3 tochange the time gap setting. This must be setsuch that the circuit doesn’t respond to shortgaps, if any, within a song and responds onlyto long gaps between different songs.Transistor T2 helps in gap-delay adjustment.The intensity of LED11 diminisheswhen a song is completed and thecounter is ready to accept the next pulse.Connect the input to the preampoutput or equaliser output of the audiosystem. Adjust VR1 and VR2 to get thecorrect audio-level indication. If you arealready using KA2281 for audio-levelindication, just connect diodes D1 and D2as shown in this circuit.Note that the counter counts the songsby detecting the gaps. Therefore any longgap within a song may cause false triggeringand the display will also be incremented.However, as this is very unlikelyto happen, the circuit shows the correctsong number almost all the time.

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