TSHWANE UNIVERSITY OF TECHNOLOGY
Combined Project for Digital Systems I (Digital Technology I)
THIS PROJECT IS COMPULSORY.
Total percentage of final mark: 20%
You have been contracted to design and DC voltmeter capable of measuring a voltage
from 0V to 15V and displaying the value measured on a 2 digit digital readout.
1. INTRODUCTION
The circuit uses an ADC to convert the analogue voltage measured to a digital value. The
ADC will be discussed during a practical session. The circuit then uses a multiplexer, adder
and comparator to perform the binary to BCD conversion. If a number is greater than 9 it will
be an invalid BCD code. We therefore compare each 4 bit number from the switch using a
comparator to determine if it is greater than 9. At the same time we add 6 to any value from
the switch using an adder. If a number is greater than 9 the output of the comparator will
select the binary value on the switch that has been added to 6. If it is not greater than 9 the
binary value on the switch is directly sent to the seven segment decoders. This is achieved
using a multiplexer.
Note: In order to complete this experiment you will need to understand BCD addition.
2. DESIGN
Step 1: Take the 4 bit binary number and check if it is greater than 9. At the same time take
the 4 bit number and add 610 to it.
Step 2: If the 4 bit number is not greater than 9 then select the A’s on the MUX (A should be
connected to the 4 bit output directly). If it is greater than 9, then select the B’s on the MUX
(The B’s should be connected to the 4 bit binary number that has been added to 6).
Step 3: The MUX output should be connected to the decoder and display of the LSD. The
MSD should be connected to the carry output of the adder.
3. BLOCK DIAGRAM
Cout
Adder
(Add 6 to switch)
MUX
A’s
Display 1
(MSD)
ADC
B’s
Out
Comparator
(Switch >9)
G
Display 2
(LSD)