This simple circuit can be used to emulate the operation of a music box. The number of notes may be limited to 10 at the most, and therefore is capable of generating a simple melody.
By: Akanksha Rathode
The circuit uses two popular integrated circuits: The timer 555 and 4017 decade counter
Operation of the circuit of music box may be learned as follows:
The left 555 is used as clock generator for the 4017 decade counter.
The operating frequency of the clock can be altered and adjusted simply by changing the value resistor R1 or by replacing it with a potentiometer 50K ensuring a 1K series resistor of 1K so that you don't accidentally move the pot to short the supply with pin7 of the IC.
When the left IC 555 clock rate is varied, the speed of the 4017 output sequence is changed proportionately which determines the musical sounds of the box
The above output signal 555 feeds the clock input of CD4017 which delivers 10 active outputs (high voltage) sequentially beginning with 0 and ending exit at junction 9.
As may be seen in the diagram the outputs 3 and 6 of the 4017 outputs are not used. This is purposely done in order to create spaces of silence in the melody from the music box.
Each CD4017 output may be seen feeding a series diode with a resistor which effectively links the corresponding resistor in series with the second resistor R2 555.
The above arrangement in conjunction with the capacitor C2, force the second 555 to oscillate at a specific predetermined frequency.
Whenever a CD4017 output is activated, the right hand side 555 oscillates at a frequency prefixed by the set R (of the outputs of 4017), in conjunction with R2 and C2. Once the entire sequence of the 4017 outputs are implemented, the IC is reset and process is repeated.
To operate the speaker transistor Q1 has to pass the saturation cutting frequency ranges to which the second 555 is configured at.
As can be seen, the project enables us to experience and achieve a sequenced set of notes as per the liking of the user. Experimenting with the values of the resistors in series with the diodes may be a good idea to start with.
You can also experiment and change the spaces and location of the "silences", by randomly leaving or choosing from the other pins of the 4017 outputs.
The music box circuit is powered with 9 volt PP3 battery or from a 9V AC/DC adapter.
Bill Of Materials for the music box circuit
- IC1 = IC2: 555 timer
- IC3: CD4017 decade counter
- Q1: TIP29 NPN bipolar transistor or the like
- R1 = R2: 33K resistor
- R3 = R5 = R9: 10K resistors
- R4 = R7 = R10: 15K resistors
- R6 = R8: 22K resistors
- R11: 470 ohm resistor
- C1: 10uF/25V
- C2: capacitor of 10nF
- D1 = D2 = D3 = D4 = D5 = D6 = D7 = D8: diode 1N4148 or equivalent
- LS: Miniature speaker 8 ohms.
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