This document describes two electronic devices: a digital voltmeter and a controlled voltage power supply. The digital voltmeter uses a PIC microcontroller, resistors, diodes, and seven-segment displays to measure input voltages between 0-5V. The controlled voltage power supply uses a PIC, DAC, op-amp, and push buttons to output a controlled voltage between 0-10V. It sends signals from the PIC to the DAC to the op-amp to produce the desired output voltage when the buttons are pressed. Biasing from a power supply is needed to operate the various components.

1. ‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬
OUR PROJECT IS 2 DEVICES :
1.DIGITAL VOLTMETER.
2.CONTROL VOLTAGE POWER SUPPLY.

2. DIGITAL VOLTMETER
 Components :
1.Pic Microcontroller (16F877A).
2. Two resistors (1200 , 330 ohm ).
3.Diode.
4. Two seven segment .

3. Purpose :
Measuring positive voltages.

4. Schematic Circuit

5. Schematic of this process.

6.  In our case … the vertical axis has values from 0 to 5 (volts) … and
ADC samples the signal from 0 to 1023 ( 1024 value) …
approximately , one sample is 0.0049 ... (5/1024) …. And every
value of voltage has an equivalent value of sampling…
 So , the pic reads the value of sampling and multiply it with 0.0049
to get the real value of voltage.
 We used mikroC IDE …it has many built in functions …
 one of them : ADC_READ() … we used this function to do these
steps…
 After we could determine the value of voltage , we display it on
the 2 seven segment .

7.  The 2 common anode seven segment are connected on the same
lines..
 We used an algorithm to display the 2 numbers on the 2 sev seg.
 The algorithm briefly : turn on the first and turn off the second…. and
send the data of the first one..
 Then turn off the first and turn on the second and send the data of the
second…and so on …
 This operation is performed very fast …(high frequency) …
 So we see the 2 seven segment are on and the number is displayed..

8.  Finally: we put a diode in the input voltage to
protect our pic from the negative voltage .
 For sure we take in consideration the voltage
drop on the diode ..

9. CONTROL VOLTAGE POWER SUPPLY.
 COMPONENTS:
1.FIXED 15/-15 VOLT POWER SUPPLY COMPONENTS.
2.pic16F877A.
3.DAC 0808.
4.op-amp 741.
5.Push buttons.

10. Purpose:
Control the voltage by push buttons …
The output range is from 0 to 10 volts.

11. Brief Algorithm :
The 2 push buttons increase and decrease the
voltage by giving a signal to the pic…and the pic
send out a signal to the DAC…and the DAC send
a signal to the op-amp … and the op-amp give
us the wanted voltage.

12. Schematic circuit

13. Step by step algorithm :
 Firstly we explain the components:
1.DAC : (digital to analog converter) is a chip used for taking a
digital signal and do some functions on it to output an analog
signal with a specific range.
Our chip is DAC 0808…it has 16 pins …8 of them are for the
input signal…it takes a port in the pic …so it takes a range of
numbers from 0 to 255 (256 value) …then it sends out a voltage
in another range (0 to 5 volt)…
In fact .. the output voltage is negative…
Here , the role of the op-amp comes.

14. 2.The op-amp: (operational amplifier ) is a chip used for
many purposes…
Explicitly we deal with the op-amp as a black box …we
don’t know yet the internal construction of this IC.
In our case ..we used it for 2 purposes…
For inverting and amplifying….
Briefly , the op-amp has 2 input terminals (positive and
negative) and an output terminal…

15. In our case : the positive terminal is connected to the
ground …and the negative is connected to the output
with a resistor…
Typically , the op-amp makes feedback from the output
to the input many times in order to make the two terminals
have the same voltage.
So , the 2 input terminals have 0 volt.

16.  In addition to the op-amp input terminals have a very
high impedance …so that no current enters it and no
voltage is wasted..

17. Biasing required
 the DAC requires 10 volt and -15 volt biasing. (those are
taken from the power supply).
 the op-amp requires 10 volt biasing .(from the power
supply too).
 The pic requires 5 volt biasing. (from the supply too ).

18.  For more information about :
1.Microcontroller : ask ahmad.
2.About pcb and software : ask sabry.
3.About electronic components : ask
sherbiny.