## Introduction: Theremin: an Electronic Odyssey [on 555 Timer IC ] *(Tinkercad)

In this experiment, I have designed an Optical Theremin using a 555 Timer IC. Here I'll show you how to generate music (close to it :P ) without even touching the musical instrument. Basically this instrument is called as Theremin, originally constructed by a Russian scientist Léon Theremin.The original theremin used radio frequency interference caused by the movement of the player's hand to change the pitch of the instrument. This optical theremin depends on the intensity of light that falls on a photoresistor which can be controlled by the movement of the player's hand. I'll try to explain the every stage of the circuit also. I hope you'll love this practical implementation of Electronics which you would have studied in your college.

Don't have Electronics components? OR You fear playing with electronics stuffs? Hey, No need to worry!

I have designed this whole circuit virtually on Tinkercad (www.tinkercad.com). Check it out and play with electronics by designing actual stuff and also run them (simulation).

## Step 1: Components Required

Here's the list of all the essential components needed to build this circuit:

1) 555 Timer IC

2) 10 kOhm Resistor

3) LDR (Photoresistor)

4) 100 nF Capacitor

5) Piezo (Buzzer)

6) +9 V Battery & Power DC Jack (5.5mmx2.1mm)

First of all, design this whole circuit on tinkercad to get an idea! You can also check the basic circuits output on tinkercad. I have attached the csv file containing list of all components for reference.

## Step 2: Circuit Design & Working

Basically 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip-flop element.

There are various modes of application of 555 Timer IC, depending on how we configure it.

The 555 Timer IC can be connected either in its Monostable mode thereby producing a precision timer of a fixed time duration, or in its Bistable mode to produce a flip-flop type switching action. But, here we are connecting the 555 timer IC in an Astable mode to produce a very stable 555 Oscillator circuit for generating highly accurate free running waveforms whose output frequency can be adjusted by means of an externally connected RC tank circuit consisting of just two resistors and a capacitor.

In out circuit you can see the RC tank circuit , where LDR ( Light Dependent Resistor) is also acting as part of RC tank circuit along with 10k Ohm Resistor & Capacitor.

BASIC WORKING: By simply moving our hand over the LDR, we are changing the amount of Light falling on the LDR, which is changing the light intensity & hence it overall resistance. More the Light, Least the resistance & Vice-versa. So, by changing the resistance of LDR, we are changing the RC time constant of the overall circuit which is overall changing the Frequency of this circuit (square pulses generated by 555 Timer IC) by the changed charging & discharging time of Capacitor.

Full Explanation:

When the 555 is in astable mode, the output from pin 3 is a continuous stream of pulses (square waves).

Pin 2 is the Trigger pin (used to trigger the the circuit components), it will be connected to ground through a capacitor. The charging and discharging of this capacitor switches on pins 3 and 7. Pin 3 is the Output pin. In this circuit it outputs a square wave signal. Pin 4 is the Reset pin. This pin is connected to the positive side of the battery. Pin 6 is the Threshold pin.

The capacitor will charge up and when it reaches about 2/3 Vcc (voltage from the battery), this is detected by the Threshold pin. This will end the timing interval and send 0 V(Volt) to the Output pin 3 (switches it off). Pin 7 is the Discharge pin. This pin is also switched off by the Threshold pin 6. When pin 7 is switched off it cuts the power to the capacitor which causes it to discharge. Pin 7 also controls timing. Pin 7 is connected to the 100K ohm resistor (LDR) and Changing the value of the 100K ohm resistor (LDR) changes the timing of pin 7 and thus changes the frequency of the square wave output by pin 3. Pin 8 is connected to the positive power supply (Vcc).

The 555 chip is in astable mode which means that Pin 3 is sending a continuous stream of pulses between 9 volts and 0 volts (square wave signal). In the following circuit I have modified the standard 555 square wave generator by replacing the 100k ohm resistor with a Light Dependant Resistor (LDR) or photoresistor. I have also added a piezoelectric speaker to convert the waves into sound.

This is how sound is generated using 555 Timer IC & LDR. I hope you guys understood the logic. If you guys didn't understood the astable mode logic, then please read a little about all the different modes of it, then it'd be more easier to understand. Still any doubts? Feel free to ask

## Step 3: Simulation Output & Result

Please see the circuit simulation (Oscilloscope Output) and its Actual working of the circuit I designed on the breadboard through the Video. Hope you liked the spooky sounds :P (Motorbike Starting).

Point to Observe: Note that initially I am not putting any torch light and almost covering it with my hand to block light,then I am getting very LOW FREQUENCY sound! While moving hand slightly up, its getting more light and hence the Frequency is slightly increasing. But when I put the Torch light, then the frequency jumps to much Higher frequency suddenly due to large amount of light!. See, how you can play with it to generate different frequency sounds.