This document describes the design of a digital tool to measure the length of babies in hospitals. It would use a moving sensor and timer counter to measure length. When the sensor is on and timer counting, it would measure the length by counting seconds and multiplying by 5 cm per second. The circuit would use flip-flops to count time on a display from 0-15 seconds. It would also include a static sub-circuit that always outputs 5. A multiplication sub-circuit would multiply the time by the static value to calculate length for display on a seven segment output.

1. Digital Length
Measuring
Circuits and sub circuits – How it works
Asmaa Ayyash
COMPUTER ENGINEERING STUDENT Istanbul- Turkey

2. Digital length measurement
Suppose I will design a digital tool for a hospital , that can
be able to measure the length of the babies in their early
days ..
As I will suppose that the tool will be Always on ( means it
will always be 1 )
So the input will be the moving sensor (Ms) , and the
timer counter (Tc)
The description of the mechanism :
As I supposed the machine will always be on, So When
The sensor of the machine be on , and the timer start to
count , the machine will measure the length of the baby ,
then ..
As indicated : the machine won’t be able to measure the
length unless the moving sensor is on (1) , and the time
Counter is on (1) .

3. Variables :
Ms : the moving Sensor of the tool .
Tc : the time require for measure each variable ..
Ms Tc
0 0
0 1
1 0
1 1
So According to the truth table , there is only one state at
which the digital tool will be on and doing its work
( measuring ) .

4. General Idea
So , Starting with the idea of the project :
When the moving sensor is on and the time counter
is on , the time counter is starting to count the
number of second , then at a specific time when it
complete the measurement you will stop the
counter and using a static value equal to five ..
means that every second it measures 5 cm , then it
will multiply the number of second counted by the
static value then display the measurement .
Then for each circuit :
First circuit is the time Counter circuit which is
consisting of four flip – flop to count automatically
and sequiencially ,, counting on a 7 segment display
by reset the frequency , then the counter will count
from zero to 15 ..
The MultiSim Diagram is attached :

6. The second circuit will be the static circuit which
value is always five , and the diagram will be as
follow :
The value will always be 5 .
( Static Sub Circuit ) .

7. Then the next Sub Circuit is the Multiplication Sub
circuit : which is responsible for multiplying the
number of second appears on the counter to the
static Sub circuit .
The Multiplication truth table :
a b Output
0 0 0
0 1 0
1 0 0
1 1 1
Which mean we use AND gate .
In multiplication we multiply each digit from the
first input to the all digits of the second input
Then shifting one digit for each digit multiplying .
After that we use parallel adder consisting of 4 full
adders to calculate the partial product
Then the summation of the all digit multiplications
and produce 8 out put , and if we need 4 input we

8. can consider the last 4 digit as an over flow and just
take the first four digit .
4 Parallel Full Adders

10. Since we always multiply by either 0 or 1, the partial products
are
always either 0000 or the multiplicand
There are four partial products which are added to form the
result.
We can add them in pairs, using three adders.
Multiplying 4 bits by 4 bits produce 8 bits .
The last step is displaying the result from multiplying the static
sub circuit value by the time by seconds on seven segment
Which equal the length required …

12. The block diagram of the circuit is :