Piano using 555 (Group8)

PROCEDURE TO DESIGN CIRCUIT ON SOFTWARE –
• Firstly, open the software in which you want to draw the circuit
• Select the components as per the circuit diagram.
• Components should be selected from the library of the software. As per 
there rating.
• Design the circuit by properly connecting the wires.
• We are now able to stimulate the circuit.
PCB LAYOUT–
WORKING OF SQUARE WAVE GENERATOR –
How do speakers work:
In order to translate an electrical signal into an audible sound, speakers 
contain an electromagnet: a metal coil which creates a magnetic field when an 
electric current flows through it. This coil behaves much like a normal 
(permanent) magnet, with one particularly handy property: reversing the 
direction of the current in the coil, flips the poles of the magnet.
Inside a speaker, an electromagnet is placed in front of a permanent magnet. 
The permanent magnet is fixed firmly into position whereas the electromagnet 
is mobile. As pulses of electricity pass through the coil of the electromagnet, 
the direction of its magnetic field is rapidly changed. This means that it is in 
turn attracted to and repelled from the permanent magnet, vibrating back and 
forth.
The electromagnet is attached to a cone made of a flexible material such as 
paper or plastic which amplifies these vibrations, pumping sound waves into 
the surrounding air and towards your ears.
The frequency of the vibrations governs the pitch of the sound produced, and 
their amplitude affects the volume – turn your stereo up high enough and you 
might even be able to see the diaphragm covering the cone move.
To oscillate this diaphragm, we use the output from the 555 timer IC in its 
astable state.
Working of a 555 timer IC as an astable multivibrator:
Astable multivibrator is also called as Free Running Multivibrator. It has no 
stable states and continuously switches between the two states without 
application of any external trigger. The IC 555 can be made to work as an 
astable multivibrator with the addition of three external components: two 
resistors (R1 and R2) and a capacitor (C). The schematic of the IC 555 as an 
astable multivibrator along with the three external components is shown
below.
The pins 2 and 6 are connected and hence there is no need for an external 
trigger pulse. It will self-trigger and act as a free running multivibrator. The rest 
of the connections are as follows: pin 8 is connected to supply voltage (VCC). 
Pin 3 is the output terminal and hence the output is available at this pin. Pin 4 
is the external reset pin. A momentary low on this pin will reset the timer. 
Hence when not in use, pin 4 is usually tied to VCC.
The control voltage applied at pin 5 will change the threshold voltage level. But 
for normal use, pin 5 is connected to ground via a capacitor (usually 0.01μF), so 
the external noise from the terminal is filtered out. Pin 1 is ground terminal. 
The timing circuit that determines the width of the output pulse is made up of 
R1, R2 and C. The following schematic depicts the internal circuit of the IC 555 
operating in astable mode. The RC timing circuit incorporates R1, R2 and C.
Initially, on power-up, the flip-flop is RESET (and hence the output of the timer 
is low). As a result, the discharge transistor is driven to saturation (as it is 
connected to Q’). The capacitor C of the timing circuit is connected at Pin 7 of 
the IC 555 and will discharge through the transistor. The output of the timer at 
this point is low. The voltage across the capacitor is nothing but the trigger 
voltage. So, while discharging, if the capacitor voltage becomes less than 1/3 
VCC, which is the reference voltage to trigger comparator (comparator 2), the 
output of the comparator 2 will become high. This will SET the flip-flop and 
hence the output of the timer at pin 3 goes to HIGH. This high output will turn 
OFF the transistor. As a result, the capacitor C starts charging through the 
resistors R1 and R2. Now, the capacitor voltage is same as the threshold
voltage (as pin 6 is connected to the capacitor resistor junction). While 
charging, the capacitor voltage increases exponentially towards VCC and the 
moment it crosses 2/3 VCC, which is the reference voltage to threshold 
comparator (comparator 1), its output becomes high. As a result, the flip-flop 
is RESET. The output of the timer falls to LOW. This low output will once again 
turn on the transistor which provides a discharge path to the capacitor. Hence 
the capacitor C will discharge through the resistor R2. And hence the cycle
continues.
Thus, when the capacitor is charging, the voltage across the capacitor rises 
exponentially and the output voltage at pin 3 is high. Similarly, when the 
capacitor is discharging, the voltage across the capacitor falls exponentially and 
the output voltage at pin 3 is low. The shape of the output waveform is a train 
of rectangular pulses. The waveforms of capacitor voltage and the output in 
the astable mode are shown below.
While charging, the capacitor charges through the resistors R1 and R2. 
Therefore, the
charging time constant is (R1 + R2) C as the total resistance in the charging 
path is R1 + R2.
While discharging, the capacitor discharges through the resistor R2 only. Hence 
the discharge time constant is R2C. The charging and discharging time 
constants depend on the values of the resistors R1 and R2. Generally, the 
charging time constant is more than the discharging time constant. Hence the 
HIGH output remains longer than the LOW output and therefore the output
waveform is not symmetric.
The value of T ON (time when voltage is high) is given by: 0.693 * (R1 + R2) C
Similarly, the value of T OFF (time when voltage is low) is given by: 0.693 * R2 C
Hence the frequency of the waveform can be altered by changing the value of 
R2 or R1.
How it is used in our project:
When we press a button, firstly the circuit becomes complete and the speaker 
produces a sound. However, when we press different buttons, different sounds 
can be perceived. The reason for that is, when we press different buttons, we 
are changing the value of R2 and in turn the value of T ON and T OFF. This 
leads to the diaphragm of the speaker oscillating with different frequencies 
and hence produces different sounds.
APPLICATION OF SQUARE WAVE GENERATOR –
• It is used to produce different types of tones and sounds by changing 
the resistor values.
• We can use it as a best birthday gift for the kids.
• We can also use this circuit as a Machine gun by changing the resistor 
and capacitor values
Precaution –
• This circuit should be tried only by qualified person familiar 
with the operation.
• Make all the wirings properly.
• Make sure you design it properly before starting it.
• Perform in Teachers guidance