Title of project:
Digital voltmeter using PIC-controller
Purpose/Motives:
1. Easy
to build
2. Ranges
from 0-30v
3. Accuracy
up to 100mv
4. It
measures DC voltages
5. It
is coast effective
Schematic
diagram:
Real look of Project:
Components:
1. PIC16f72
2. 7-segmet,
3digit common cathode(multiplexed)
3. Crystal
4MHz
4. Zener
diode 5.1v
5. Voltage
regulator 7805
6. Resistor
560 ohm (8), 1k (3)
7. Transistor
BC547 (3)
8. Variable
Resistor 10k
9. Resistor
20k & 120k
10. Switch
11. 9v
battery
12. Capacitor
33pF (2)
Let’s
understand the working of this voltmeter. We use PIC16f72
IC in this project (it is the heart of this project). It has 28-pins.
We
have an ADC (Analog to digital converter).
It is a peripheral device which is built-in in our IC Pic16f72 (It has an 8bit ADC). With the help of code we can enable/disable our ADC easily.
The purpose of using ADC is that we have to measure the voltages which are
available in the form of analog signal(analog value) but we have to display
them in the form of digits on 7-segment display so that we need to convert the
input voltages into digital form by using analog to digital converter (ADC). So
the voltages which have to be measured, we apply them directly on the ADC
input. Now here we have 8-bit ADC so our input voltages will convert in 256
levels in ADC. According to formula:
No. of levels in ADC=2resolution
of ADC
So
in our case:
No. of levels in ADC= 28 =256
Since
our voltages now available in 256 levels to obtained our required voltages
value at the output of ADC we have to calculate a factor which will multiply to
the output of ADC to give required values. So we have another formula:
Multiplication factor=(Vcc/no. of levels)x100 = (5/256)x100=1.9607843
Vcc
is the input voltages of our pic IC which is maximum 5v.
We
have calculated a factor (Vcc/no. of
levels). Now if we multiply it with our
ADC
output so it gives output in mili-volts. To get the values in volts we again
multiply it by 100. So we have a total factor (1.9607843).
We
know that ADC gives the output voltages by comparing the input voltages to the
reference voltages of the PIC IC which is 5v. So ADC can give the maximum
output voltage values up to 5v only(because of reference volts). Then to get
voltages up to 30v we have multiply the ADC output to the 6 to get 30v from 5v.
Multiplexed 7-segment
We are using the word
multiplexed which means when 4 segment
displays are connected as a single segment, the data bus of all the segments
comes in parallel and the enable pin is different for all segments. In this
way, we control the individual segments by controlling each segment’s enable
individually. In our project we have done this by using switching transistor
connected between the multiplexed 7-segment and PIC IC.
Now if we select the
enable pin separately of segment so at one time only one segment would be ON
and would display remaining other would be off at that time. This
is how multiplexed seven segment display
works. But now the question is how can we show different data in these 4
segments at a time? Remember, human eyes can’t find the difference within 10ms.
I hope you already know about the persistence of vision. If we can change the
data with corresponding enable pins of all these 4 segments within 10ms, our
eyes will see a set of 4 digits in this segment. In other words, we will do the
following within 10ms to display 1234. Feed data bus with 1 and set S1 high. Feed
data bus with 2, turn S1 low and set S2 high. Feed data bus with 3, turn S2 low
and set S3 high. Feed data bus with 4, turn S3 low and set S4 high. All this
has to happen with in 10ms. Finally the process repeats to keep the display
stable.
Uses:
1. It
can be used as a panel meter
2. It
can be used in voltage supplies
3. Other
kind of DC-voltage measuring can also be done by using it.
Future horizons:
1. It
can be converted into an Amp-meter
and as a temperature sensor
2. Accuracy
can be increases upto 1-10mv
3. It
can be converted into AC-voltmeter.
4. It
can be converted into an Amp-meter
and as a temperature sensor(we has done
this just using LM35 and small change in conversion factor)
Coding:
•
Main function
•
User define functions:
Ø Short-mask
(function for 7-segment)
Ø Display
function
Specification:
Ø Can
measure DC-voltages
Ø Accuracy
upto 100mV
Ø Ranges
from 0 to 30 V
Ø Uses
multiplexed 7-segment display(3-digits)
Ø Powered
by 7 to 35 DC-voltages
