Electronic Piano using 555 Timer IC

Project: 1

-Feb '19

What is the project about?

This is a simple project which required only a few basic electronic components. This was my first project as an engineering student and hence is quite special to me.
It is a DIY electronic Piano which can produce as many numbers of notes as the number of pushbuttons and connected circuitry added. Mine had 8 notes, one corresponding to each fundamental note of music. The pitch could be adjusted by varying the resistance of the potentiometer used. My friends and I had a lot of fun later playing and composing music with it.







Understanding the working

    Circuit Diagram

    Made using CircuitLab

    Components Required

    • 555 Timer IC
    • 8 Ohm Speaker
    • Momentary Push Buttons x 8
    • Capacitors;
      • 100nF x 1
      • 10uF x 1
    • Resistors; 1kΩ x 9
    • Potentiometer 10kΩ x 1
    • Breadboard
    • 9V Battery
    • Connecting Wires

    555 Timer IC

    The 555 IC is a compact timing circuit that produces accurate and highly stable time delays or oscillations. When compared to the applications of an op-amp in the same area, the 555 IC is equally reliable and is cheap in cost.
    I used an NE555 timer IC which came in an 8 pin mini-DIP package. DIP packages are easier to handle and comfortable to work with on breadboards.



    Internal diagram of NE555 Timer IC

    The internal diagram of NE555 can be divided into 5 blocks as highlighted in rectangles in the internal diagram.

    1. Voltage Divider

    The voltage divider network has three 5kΩ resistors which give a reference input voltage to each of the two comparators in block 2.

    2. Comparators

    Two opamps are built-in to compare the input voltage of pins 2 and 3 to built-in voltages of 2/3VCC and 1/3 VCC provided by block1. Comparator UC returns a high(logic 1) if the input of pin 6 is greater than the set value of 2/3 VCC provided by the voltage divider network. This serves as set input for block 3. Similarly, the comparator LC returns a high value if the input of pin 2 is lower than the set value of 1/3VCC set by the voltage divider network again. This serves as the reset input for block 3.

    3.SR Flip-Flop
    If the input voltage at pin 6 is higher than 2/3VCC, the comparator LC returns a high output and this serves as a high set input to the SR Flip-Flop. This causes the output of the Flip-Flop to set to a high too (irrespective of the previous state of the flipflop.

    Similarly, if the input at pin 2 is lower than 1/3 VCC, Reset input of the Flip Flop receives a high input and the output of the Flip-Flop is reset to low (logic level 0).

    When both the comparators return a low, SR Flip-Flop remains in its state and no change of output occurs.

    The invalid state of the SR Flip-Flop is never countered as both the comparators can never return a high value together.

    4. Discharge Transistor
    When the output of the SR Flip-Flop is low and the complement of it is high, the transistor receives a high voltage at its base, and therefore effectively short circuits the path and allows the discharge of a connected capacitor.
    5.Output Driver
    It consists of an inverter circuit which serves as the output of the timer IC.

    The time period of the IC can be adjusted by varying the input of pins 2, 6 or 5.


    Pin Diagram of NE555 Timer IC


    Pin 1- GROUND
    Pin 8- VCC
    Pin 3- OUTPUT
    Pin 2- TRIGGER
    Pin 6- THRESHOLD
    Pin 4- RESET
    Pin 5- CONTROL VOLTAGE
    Pin 7- DISCHARGE


    Tactile Switch

    A tactile switch allows electricity to pass through it momentarily when pressed. They are cheap and are used in low voltage and current applications.
    They have 5 parts; an outer casing, a Plunger or lever which is manually pressed, a metallic dome-shaped contact, a base, and 4 terminals. The terminals are shorted in pairs internally and each pair is insulated from the other when in OFF position. When the switch is pressed, the plunger is pushed down. It is connected to a metallic contact which is also pushed down subsequently. This causes the base to serve as a path connecting the 2 pairs of internally shorted terminals, thereby completing the circuit.


    Why do tactile switches have 4 terminals instead of just two, if they are shorted internally in pairs?

    The dual shorted pins allow inexpensive single-sided printed circuit boards to be used for building X-Y matrices with tactile switches without requiring additional jumper wires for the purpose. It also improves mechanical stability.


    Simulation
    See the original;




    Circuit Construction





    Working




    External Links


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