Electronic harmonium

Electronic harmonium

Electronic Harmonium is a simple circuit that generates notes/swaras of Indian classical music system. These notes are sa, re, ga, ma, pa, dha, ni. These seven distinct notes are collectively called Sargam.

This circuit demonstrates the need of electronics in diverse fields like music in life. Let us see as to how we can transform a circuit into a melodious instrument by using simple electronic components.

Let’s get going!


The circuit layout shows the placement of different components (values, polarity). We just have to insert the components at the designated place and solder them properly on the reverse side. On the solder side, there are conducting tracks inscribed instead of wire connections. This makes the circuit neat and easy to make.

Circuit description

The circuit consists of a specially designed PCB, with 15 parallel copper tracks. The resistance of different values is mounted on each track as per layout. Each resistance corresponds to one note. So, as the probe touches different resistance, different notes are generated.

The circuit is built around IC 555. When we put the probe on different resistances, we are effectively changing the frequency between pin 2, pin7 of the IC 555.

Component side of PCB

This is the side where we will mount the components.

Solder side of PCB

Solder side contains conducting tracks to make the connections between various components. We will fix the components at their designated place by soldering.

Now follow these steps to start building the electronic harmonium:

1. Prepare the component identification data (CID) for the circuit.

2. Insert the components according to circuit layout while taking help from the markings on the PCB.

3. First mount the resistors. For the values refer to pictures as well as the post on Resistor: Value reading. Since the resistors do not have any polarity, they can be mounted either way. Turn over the PCB and bend the leads to prevent them from falling.

4. Now mount the ceramic capacitors with 222PF capacitor and 103PF capacitor according to the markings and circuit diagram. Bend the legs after mounting to prevent them from falling.

5. Now mount the IC base and the electrolytic capacitor. The electrolytic capacitor has polarity. Mount the IC base as per the notch direction on PCB. Bend the legs of the electrolytic capacitor normally but bend any two opposite pins on the IC base to prevent it from falling. Refer to the picture below :

6. Solder all of the points and cut off all the leads.

7. Prepare the 9V snap, probe wire and two additional wires for the speaker by striping them and soldering them to their points. refer to the Diagram and pictures below.

The circuit is ready. Enjoy the melodies!!!

Resistance Wheel

Resistance Wheel

Resistor is a very vital electronic component used in most of the circuits. The value of resistor is marked on it in colour coded form. There is a special code to read this value. Resistor: Value reading

In this activity, we will design a handy tool resistance wheel which will eliminate the need to memorize the values of color rings.

Material Used: Card Board, geometry box, color pencils.

  • Draw four circles on a card board of radius 5 cm, 4 cm, 2 cm and 1 cm. Mark there center. Cut these circles. Divide each circle in to 11 parts (10 parts of angle 33 degree, 1 part of 30 degree).

  • Color ten parts of the circle in the following sequence: Black, Brown, Red, Orange, Yellow Green, Blue Violet, Grey and White.

  • Label each circle as per the table given below.
  • The first and second ring is the value ring. The third ring is multiplier and the fourth ring is the tolerance one which is usually gold or silver.
Color I Ring II Ring III Ring
Black 0 0
Brown 1 1 0 Ω
Red 2 2 00 Ω
Orange 3 3 KΩ
Yellow 4 4 0KΩ
Green 5 5 00KΩ
Blue 6 6 MΩ
Violet 7 7 0MΩ
Grey 8 8 00MΩ
White 9 9 GΩ
  • Align all four circles at the centre. Make a hole at the centre of each circle.  Take a splitter nail. Insert the nail through all the circles. Bend the nail at the back.

  • Our resistance wheel is ready.