Download Digital Metronome

Digital Metronome
Planning
A1: I am going to make an electronic metronome device which produces
equally spaced sound at a variable speed which is displayed in beats per
minute.
A2:
Variable
Astable
Logic
Frequency
divide by
60
Counters
LED
Astable 1Hz
Decoders
Displays
Amplifier
Buzzer
The system consists of several sub-systems. The basis of the system is the two
astable oscillators. One oscillator is variable between frequencies of around 40300 Hz by the use of a potentiometer and the other has a fixed frequency of
1Hz.
The outputs of the two oscillators are put into the inputs of an AND gate and
the output of the AND gate is used to drive a counter.
The counter is linked to a decoder and a 7 segment display. The terminal count
output of the counter is connected to the clock input of a second counter which
is also linked to a decoder and a display and a third counter is also linked in this
way. This sub-system thus produces a 3 digit visual output showing the
frequency in Hertz of the variable astable oscillator.
The output of the variable astable is also take to a series of counters and logic
gates which divide the frequency of the output of the oscillator by 60 which
gives an output of the same frequency in beats per minute as the frequency of
the variable astable in Hertz (pulses per second). This means the display system
shows the frequency of this output in beats per minute as opposed to Hertz.
This output is then connected to an LED and a transistor amplifier wh ich is
connected to a buzzer to make buzz sounds at the frequency shown on the
display.
Sub-system in detail: Variable Astable Oscillator
This circuit diagram shows the variable frequency astable in detail. The basis of
the sub-system is a 555 IC. The reset pin is tied high to ensure that the chip
functions correctly. The control voltage (CV) pin i s tied low with a 10nF
capacitor as a frequency modulated output is not needed and the capacitor
eliminates noise. The selection of resistor and capacitor values means that the
100K potentiometer can be used to vary the frequency as shown in the
experiment later.
A3:
1. http://www.technologystudent.com
This website was used in researching some of the sub-systems of my
circuit. Information such as the correct layout of a 555 astable was
obtained from this site. This information is shown in clear diagrams and
explanations that are easy to understand.
2. http://www.kpsec.freeuk.com/components/ic.htm
This website was used to obtain all the necessary IC pinots needed to
build my system. The diagrams are clear and easy to read.
A4: Investigation into frequency of astable
The following investigation was carried out on the variable astable: The
resistance value of the potentiometer was varied and the resulting frequency of
the oscillator was recorded.
These are the results which were obtained:
Resistance of Potentiometer (Kfi)
0
10
20
30
40
50
60
70
80
90
100
Frequency of Oscillator (Hz)
304
57
33
24
17
12
10
9
8
8
7
These results and this graph show that as the resistance of the potentiometer
increases, the frequency of the oscillator decreases. The rate of decrease in
frequency is rapid at first but becomes much more gradual at a resistance of
around 10Kfi.
A5:
My specifications for this project are:
1. The circuit must work with a 9v + 1v power supply so that it is able to
operate with a 9 volt battery as well as a power supply.
2. The metronome must operate at speeds of 40 – 300 beats per minute
3. The system must have a display output showing the speed of the
metronome in beats per minute accurate to + 10%
A6:
Instead of using seven segment displays to show the speed, I could have used a
different display system such as an LCD display. An LCD display would be
capable of showing the same information as he seven segment displays and
would possibly look much neater.
The reasons I decided to use seven segment displays
over and LCD display are:
1. AIthough the system wouId take up Iess space on
its own, it may end up using more space on the
board than the seven segment dispIays as it couId
possibIy need a Iot of decoders.
2. Also I understand how seven segment displays work but I do not know
anything about the workings of an LCD display so the use of it would
require a lot of research ad I would be more likely to make mistakes hen
using it.
A8:
A9:
Resistors
I have used the following resistors in my circuit:
4.7Kfi for the timing mechanism of the oscillators
● 1.2Kfi for protecting the 7 segment displays
● 100fi to protect the LED and the rest pin of the counters in my
frequency divide by 60 sub-system
● All resistors have a tolerance of + 5%
The rail voltage of the circuit will be 9vand the maximum current flowing will
be 10mA
●
P =V x I
=9 x 10ma
=90mW
So 0.25 Watt resistors will work fine in my circuit.
Oscillators
In a 555 astable the time period is (R1 +2R2)C / 1.44
For the 1Hz astable a time period of about 1 second is required
(4700 +2*4700)*0.0001 / 1.44 = 0.979 (3sf)
Therefore the resistors used will both be 4.7Kfi and the capacitor will be 100µF
as 0.979 is very close to 1.
Realisation of a system
B2:
B2:
When constructing my circuit, I took great care to ensure that all polarised
and active components were correctly orientated
B3:
Whilst working on my circuit I made sure to take safety into account. In order
to do this I did things such as checking the polarity of any chips I used, and
checking that I used the correct voltage on my power supply .
B4:
Resistance of Potentiometer
Read-out on display
0
315
20
36
40
16
60
9
80
8
100
6
These results show that the display system works as the numbers displayed are
within 10% of the frequency recordings taken earlier.
B5:
Resistance of potentiometer
Final Frequency of pulses (Hz)
0
5.13
20
0.58
40
0.25
60
0.15
80
0.12
100
0.09
This proves that the whole system works as the frequencies obtained at the
end are equal to within 10% of the original frequency of the astable divided by
60.
B6:
The first time I tested my circuit, it worked.
B7:
There were no faults to fix as the circuit worked on the first try.
Testing andEvaluation
C1:
To record data for the frequencies of the components in my circuit, I used a
oscilloscope to determine the time period of the waves and then calculated the
frequency by dividing 1 by the time period. For testing voltages I used a multimeter as volt meter on the 20K setting and to probe leads.
C2:
I have recorded measurements relevant to my specifications as I have recorded
the frequencies of the pulse that drives the buzzer ad LED at the end of the
circuit and also taken readings from the 3 digit display to see how these match
up to the actual frequencies of the pulse. The frequencies appear to match up
to a certain degree of accuracy so the circuit works as it was intended.
C3:
My circuit worked as I intended which was for it to be an “ electronic
metronome device which produces equally spaced sounds at a variable speed
which is displayed in beats per minute”. I have also met all of my original
objectives:
1. The circuit must work with a 9v + 1v power supply so that it is able to
operate with a 9 volt battery as well as a power supply.
All tests were conducted using a power supply on a 9 volt setting and the circuit
worked as required.
2. The metronome must operate at speeds of 40 − 300 beats per minute
As shown in the tests above the metronome operates at speeds of 6 to 308
beats per minute.
3. The system must have a display output showing the speed of the
metronome in beats per minute accurate to + 10%
As shown in the tests above the display shows a reading which is within 10% of
the speed of the metronome beats.
C4:
As the circuit worked as desired, there was no need to make any
improvements to its workings.