05-10-2012, 12:25 PM
AN ELECTRONIC HARMONIUM
[attachment=35379]
How it works
This harmonium can generate 15 different notes of
music (one at a time). It has a PCB with 15
switches. Each switch corresponds to one note. So,
as you press the switch, the instrument plays a
corresponding note.
Now let us have a look at the functioning of 555 as
an oscillator. If we assume that 555. has been given
a 9-volt power supply across pins 1 and 8, it exhibits
the following properties:
1. When voltage on pin 2 falls below 3 V, out put at
pin 3 is switched to +9V and pin 7 acts as 'open)
circuited'. Any change in voltage level at pin 2 will
not change the state of IC now.
2. When voltage on pin 6 goes above 6V, pin 3
switches to 0V level and pin 7 acts as if it has been
short circuited to ground. Any change in voltage of
pin 6 will not change the state now.
In our circuit, we have connected pins 2 and 6
together. So if we assume that output at pin 3 is
9V, at a particular instant the combination of R1 and
Rk (R2 to R16) charges capacitors C3, and voltage
across the capacitor keeps on increasing.
Warning
VISHA kits are sold as stand alone training kits.
If they are used as part of a larger assembly and
any damage is caused, our company bears no
responsibility.
When it becomes slightly more than 6V, pin 6
senses it and changes output voltage at pin 3 to
0V and pin 7 starts acting as if it has been
shorted to the ground. So C3 starts discharging
through Rk. As soon as pin 2 senses that voltage
across the capacitor is less than 3V, output is
switched back to 9V. So the cycle repeats itself.
This way we get square waves at pin 3. Since
capacitor C3 charges and discharge through Rk,
the charge and discharge times can be varied by
changing values of Rk and in turn the frequency
of square wave can be changed. The values of
R2 to R16 (which represent Rk) have been
calculated to give the correct ratio within 2 per
cent tolerance.
[attachment=35379]
How it works
This harmonium can generate 15 different notes of
music (one at a time). It has a PCB with 15
switches. Each switch corresponds to one note. So,
as you press the switch, the instrument plays a
corresponding note.
Now let us have a look at the functioning of 555 as
an oscillator. If we assume that 555. has been given
a 9-volt power supply across pins 1 and 8, it exhibits
the following properties:
1. When voltage on pin 2 falls below 3 V, out put at
pin 3 is switched to +9V and pin 7 acts as 'open)
circuited'. Any change in voltage level at pin 2 will
not change the state of IC now.
2. When voltage on pin 6 goes above 6V, pin 3
switches to 0V level and pin 7 acts as if it has been
short circuited to ground. Any change in voltage of
pin 6 will not change the state now.
In our circuit, we have connected pins 2 and 6
together. So if we assume that output at pin 3 is
9V, at a particular instant the combination of R1 and
Rk (R2 to R16) charges capacitors C3, and voltage
across the capacitor keeps on increasing.
Warning
VISHA kits are sold as stand alone training kits.
If they are used as part of a larger assembly and
any damage is caused, our company bears no
responsibility.
When it becomes slightly more than 6V, pin 6
senses it and changes output voltage at pin 3 to
0V and pin 7 starts acting as if it has been
shorted to the ground. So C3 starts discharging
through Rk. As soon as pin 2 senses that voltage
across the capacitor is less than 3V, output is
switched back to 9V. So the cycle repeats itself.
This way we get square waves at pin 3. Since
capacitor C3 charges and discharge through Rk,
the charge and discharge times can be varied by
changing values of Rk and in turn the frequency
of square wave can be changed. The values of
R2 to R16 (which represent Rk) have been
calculated to give the correct ratio within 2 per
cent tolerance.