Project 2

555 Piano

Overview

Now that you have created a basic circuit and soldered on a protoboard, let's explore integrated circuits! You will build two circuits using a 555 Timer IC: (1) a blinking LED circuit, (2) a three-key electronic piano.

Concepts


Ceramic Capacitors

A capacitor is a component that briefly stores electrical energy, which it charges and discharges in bursts. It is not a battery. Batteries store energy at a high density and slowly charge and discharge that energy.

The ability of a capacitor to store energy is its capacitance, measured in farads (F).

The higher the capacitance, the longer it can store energy. Naturally, the capacitor will also take more time to charge and discharge.

Common Uses

Capacitors can be used to block low frequency AC current, as is the case with our 555 Piano. A capacitor in series with the piezo buzzer filters out the low frequencies to produce clean sound.

We will also use a capacitor to configure the NE555P IC. The time it takes for the capacitor to charge and discharge determines the delay of the IC.

Capacitor Markings

You can determine the capacitance of a ceramic capacitor from its 3-digit markings. As shown on the right, the first two digits are multiplied by 10 raised to the power of the third digit. The product is the value of the capacitor measured in picofarads.

Symbol

Our projects make use of ceramic capacitors which have no polarity. Non-polar capacitors are represented by the schematic symbol on the right.

Pushbutton

A pushbutton is a type of switch. It completes a circuit when pressed and disconnects the circuit when released.

Pushbutton Legs

The figure shows that the legs labeled 1 are internally connected. This pair of legs acts as one node in our circuit. The same is true for the legs labeled 2.

Legs 1 and 2 are connected only while the button is pressed. This means that when the button is pressed, all four of its legs are connected as a single node.

Symbol

Though pushbuttons have four legs, their schematic symbol reduces the complexity to two terminals (as depicted in the figure). We can think of legs 1 as one terminal and the legs 2 as the opposite terminal.

Piezoelectric Buzzer

A piezoelectric buzzer is a component used to emit sound.

Piezo buzzers come in two varieties: active and passive. Active buzzers have a built-in oscillator with a set frequency that cannot be changed. Passive buzzers do not; they have to be fed an oscillating signal.

We will use a passive piezo buzzer.

Symbol

The symbol on the right depicts a non-polar piezo buzzer. The symbols for speakers and piezo buzzers are often used interchangeably.

NE555P IC

The 555 Timer is one of the most popular integrated circuits for hobby projects. It has multiple use cases, but we will operate the timer in astable mode. In this mode, it outputs an oscillating digital waveform (see the image below), which we will feed to the piezo buzzer.

Remember that the frequency of the waveform is the same as the pitch of the buzzer sound.

Pinout Diagram

We will use the NE555P, a variant of the 555 Timer. Its pinout diagram is shown below.

The pinout diagram identifies each contact or pin of the IC. Usually, a datasheet will include a pinout and a table that matches each pin with a description. The pinout may change depending on the IC’s packaging, which the datasheet will indicate. For this project, the IC package is DIP.
Note that the organization of the pinout differs from the schematics below. The true location of the ICs pins is shown by the pinout, not the schematic. Use the notch on a DIP-style IC to find its correct orientation.

How It Works

Learn more about 555 Timer’s functionality in the lecture material here.

Printed Circuit Board (PCB)

Breadboards and protoboards are great for prototyping simple circuits. However, when electronics are more complex or are ready for production, we typically use printed circuit boards or PCBs. Nearly every device, from a digital alarm clock to a laptop computer, uses a PCB. It is a board designed with CAD software, that connects individual components.

The benefits of PCBs over prototyping boards are numerous: They're more compact, more reliable, and enable complex circuit design. Above all, they are easy to mass produce.

For this project, you will solder the 555 Piano to a PCB we designed in a software called KiCAD (as seen below). If you are not enrolled in the course, you may alternatively use a perfboard.

Soldering to a PCB is much like soldering to a protoboard, and you may even find it easier. For more soldering tips visit our workshop material here.

Requirements

For readers who are enrolled in the course: In order to receive full marks on your project submission, make sure it meets the following minimum requirements.

555 LED Blinker

  • You must build a blinking LED circuit.
  • The LED in the circuit must cycle at a rate of roughly once per second.
  • The LED must be brightly lit when turned ON.
  • The LED must be completely dark when turned OFF.
  • The circuit must be built on a breadboard.

555 Piano

  • You must build an electronic “piano” circuit with three buttons.
  • The circuit must emit a distinct tone for each of the three buttons pressed.
  • When a button is pressed, the piezo should emit minimal static noise.
  • The circuit must emit tones at a reasonable volume (not too low).
  • The circuit must be soldered to the provided PCB.

Parts

Part Name Qty
Breadboard 1
Battery (9V) 1
Dupont 9V Snap Connector 1
Header, 2.54mm, Female, 1x2 2
NE555P IC 1
Resistor, 1kΩ 3
Resistor, 4.7kΩ 1
Resistor, 470kΩ 1
Switch, Tactile 3
Dip Socket, 8 pin 1
LED, 3.2V 1
Capacitor, 0.1µF 1
Capacitor, 1µF 1
Capacitor, 10µF 1
555 Piano PCB or Perfboard 1
Piezo Buzzer, 1.5V 1
Jumper Wire ?

Schematics

Instructions

Checkpoint 1

  1. Build the circuit from Schematic A on your breadboard.
  2. Verify that the circuit meets the design requirements. Before proceeding to the next checkpoint, make sure you have created the required deliverables.

Checkpoint 2

  1. Deconstruct the circuit you built in Checkpoint 1 and reuse the components to build the circuit from Schematic B (the piano) on the breadboard.
  2. Verify that the circuit meets the design requirements (no soldering required yet). Before proceeding to the next checkpoint, make sure you have created the required deliverables.

Checkpoint 3

  1. Enrolled Students: Solder the circuit components from Schematic B to the provided PCB.

        If you do not have a PCB, you may use a protoboard/perfboard instead.

Deliverables

Students enrolled in the course must submit the deliverables below to the corresponding Canvas course assignment.

Place the following files in a single folder:

  • Video of the 555 LED Blinker (Schematic A) circuit on a breadboard
  • Video of the 555 Piano (Schematic B) circuit on a breadboard
  • Video of the 555 Piano (Schematic B) circuit soldered to the PCB

Compress the folder to a zip file and rename the file using the format “ops_project#_lastname_firstname.zip” Then, submit the zip file to the Project 2 Canvas assignment.