Electroposium

AUTOMATED SOLDERING ROBOT

2013-03-30T13:47:00.000-07:00

I will come up with the description soon. Meanwhile, have a look at the video.

PLOTTING 3D GRAPHS USING MATLAB

2013-02-21T10:33:00.000-08:00

In continuation to my post PLOTTING 2-D GRAPHS USING MATLAB which explained plotting various 2-D graphs and defining graph, figure, colour and background properties etcetera, my current post explains plotting 3-D graphs and related functions.

To start with, the function used here is plot3( ) for plotting 3-D graphs. We will plot a sphere and before it let us see the code to plot a circle centred at (2,2) of radius 2.

x=0:0.01:4;
y=((4-(x-2).^2).^0.5)+2; % semicircle for y>0
plot(x,y)
hold on
y=-((4-(x-2).^2).^0.5)+2; % semicircle for y<0
plot(x,y)

Keeping the above example in mind let us plot a sphere centred at (2,2,0) of radius 2.

for i=-20:20 % for plotting 40 circles.. u can increase or
% decrease
z=i/10; % z can obtain the values from -2 to +2 in a
% sphere with centre (2,2,0) and radius 2
r=(4-z*z)^0.5; % r is radius of circle in xy plane, equation
%of a sphere is x^2+y^2+z^2=2^2 and x^2+y^2=r^2
x=2-r:0.01:2+r;% as 2,2 is the centre of xy plane
a=x./x; % a converted to a vector of same size as x
z=z*a;
y=((r^2-(x-2).^2).^0.5)+2; % circle eqn
plot3(x,y,z)
hold on
y=-((r^2-(x-2).^2).^0.5)+2;% circle eqn
plot3(x,y,z)
end

In order to study the 3-D plot from every angle, MATLAB provides "Rotate 3D" feature which is demonstrated by rotating the above plotted sphere to an angle.

There are some more codes by which a sphere can be drawn. Let us plot a sphere of radius 2 by using polar coordinates.

r=2; % radius 2
o=0:0.1:2*pi; % theta
for i=0:31.4
h=i/10; % phi
x=r*sin(o)*cos(h);
y=r*sin(o)*sin(h);
z=r*cos(o);
plot3(x,y,z);
hold on
end

One of the function available in MATLAB is meshgrid( ). Let us see how we can plot a 3-D plot with its help.

like for e.g.

a= [1 2 3];

b=[6 7 8];

and we want to have elements (1,6) , (1,7), (1,8), (2,6), (2,7), (2,8), (3,6),(3,7), (3,8)

then [X,Y]=meshgrid(a,b) solves our problem

as it creates X= 1 2 3 Y= 6 6 6

1 2 3 7 7 7

1 2 3 8 8 8

Now see the following code to generate the sphere via meshgrid( )

a=-1:0.05:1; % an array
b=-1:0.05:1; % another array
[x,y]=meshgrid(a,b); % generates all the possible coordinate
%range from (-1,-1) to (1,1)
z=(1-(x.^2+y.^2)).^0.5; % equation of sphere with radius 1 and
%origin as centre
for i=1:41
for j=1:41
if imag(z(i,j))==0 % check to plot only real values that
%satisfy the eqn of sphere as they are
%the true values
plot3(x(i,j),y(i,j),z(i,j)) % plotting individual points
hold on
end
end
end

hold on
z=-((1-(x.^2+y.^2)).^0.5);
for i=1:41
for j=1:41
if imag(z(i,j))==0
plot3(x(i,j),y(i,j),z(i,j))
hold on
end
end
end

Using the meshgrid function and polar coordinates we have the following code for a sphere.

r=2; % radius =2
phi=linspace(0,pi,50); % phi=0 to pi divided in 50 slots
theta=linspace(0,2*pi,50);
[phi,theta]=meshgrid(phi,theta);

x=r*sin(phi).*cos(theta);
y=r*sin(phi).*sin(theta);
z=r*cos(phi);
plot3(x,y,z)

Now let us plot some other figures.Following is the code to plot a cone

o=pi/4; % apex angle/2
l=5;
for h=0:0.01:l*cos(o); % height from min to max
r=(l*cos(o)-h)*tan(o); % radius of the circle to pe plot in x,y plane
x=-r:0.01:r; % range of x
z=(x./x)*h; % z converted to a vector of same size as x
y=(r^2-x.^2).^0.5;
plot3(x,y,z);
hold on
w=-(r^2-x.^2).^0.5;
plot3(x,w,z);
hold on
end

Now let us plot a cube with 4 sides of side length 2 :-

x=0:0.01:2;
y=(x./x)*0;
w=(x./x)*2;
for a=0:0.01:2
z=(x./x)*a;
plot3(x,y,z) % xz plane plotted at y=0
hold on
plot3(x,w,z) % xz plane plotted at y=2
hold on
plot3(w,x,z) % yz plane plotted at x=2
hold on
plot3(y,x,z) % yz plane plotted at x=0
hold on
end

Now let us plot a line with direction cosines(2,1,1) and passing through (1,2,3)

k=-5:0.01:5;
x=2*k+1;
y=k+2;
z=k+3;
plot3(x,y,z)

Now let us plot a plane with equation 2x + 3y + 5z =10

a=0:0.1:5;
b=0:0.1:5;
[x,y]=meshgrid(a,b);
z=(10-(2*x+3*y))./5;
plot3(x,y,z,'b')

Now let us plot a cylinder of radius 2 and height 4.

r=2;

h=0:0.1:4;

theta=0:0.1:2*pi;

[H,THETA]=meshgrid(h,theta);

R=H./H.*r;

x=R.*cos(THETA);

y=R.*sin(THETA);

z=H;

plot3(x,y,z,'b');

3-D BAR GRAPHS AND PIE CHARTS

We learned to plot 2-D bar graphs and pie charts in my previous post. Now taking the profits of two companies in the corresponding years we will study 3-D bar graphs and the function used to plot the same is bar3( ).

year1= [2005 2006 2007 2008 2009 2010];
profit1=[500.43 600.76
562.62 970.45
357.81 1100.3
597.39 708.7
624.61 300.34 %first column company A
731.98 900.32 ]; %second column company B
bar3(year1,profit1,0.6);% default detached
title('detached');

Keeping all the rest statements same and changing the last two, in the above program, let us see some variations.The first is grouped and the other is stacked.

bar3(year1,profit1,'grouped');
title('grouped');

bar3(year1,profit1,'stacked');

title('stacked');

Let us now have a look at 3-D pie charts and the function used for it is pie3. Suppose we have 52 engineering, 24 medical ,16 art, 20 pharma and 80 maths students.
a=[52 24 16 20 80];
pie3(a);

Let us see a variation in the above code.
a=[52 24 16 20 80];
b=[1 0 0 1 0];
pie3(a,b);

This ends the basics of graph plotting in MATLAB.

SEMI/FULLY AUTOMATIC WATER PUMP DRIVER SYSTEM USING LOGIC GATES

2012-03-04T02:05:00.283-08:00

Everyone uses submersible or normal water pumps to fill overhead tanks of their buildings or bungalows. These pumps are still operated manually by majority of people. Sometimes, the water pump may run dry in case of low water level. This may cause an internal damage to the pump. Sometimes, user may forget to switch it off resulting in overflow of overhead tank and wastage of water.

In my previous post FLOWING WATER INDICATOR, I mentioned about overcoming this problem but still it was manual and I also mentioned about the best solution i.e. using SEMI/FULLY AUTOMATIC PUMP DRIVER SYSTEM.

This system reduces human effort and completely avoids wastage of water and provides safe running of water pump.

A fully automatic pump driver system intelligently switches on the water pump if the overhead tank gets empty below a certain level and if there is adequate water in the underground tank and it needs no human intervention. It will also switch it off or keep it switched off, if the overhead tank is full or in case of low water level in the underground tank.
In the semi-automatic mode user will have to switch on the pump manually and the pump would get off automatically. This mode is useful in summers in scarce water conditions.

Usually, these types of systems are made using micro-controllers which increases the cost of circuit and makes it complex. Making it using logic gates, makes it cheaper.

It also makes it easier to be implemented by anyone who has a little knowledge of Boolean algebra and electronics.

AUTOMATIC PUMP DRIVER SYSTEM

First, consider the image of a common water system :

In order to create an automatic pump driver system, signals from underground tank and overhead tank are required to find their status.

We put sensors for the same. In automatic system we require 6 sensors: 3 for overhead tank and 3 for underground tank.

Brass screws can be used as sensors as they do not rust but with time a scale gets deposited on their surface and they become non conducting and have to be replaced. Definitely it is a drawback but this is not a major worry as the process is very slow.

Let us consider the requirements of our system:

1) OVERHEAD TANK

The system should receive a signal when the overhead tank is full and also when the water level is below a particular level (which is considerd empty)

So we require two sensors ‘Overhead Tank Full’ and ‘Overhead Tank Empty’ for the same. Third one will be common anode for providing +5V. System won’t receive any signal from it.

2) UNDERGROUND TANK

The system should receive a signal when underground tank is empty and when water level has reached a particular level. So we have two sensors for the same: ‘Underground Tank Sufficient’ which says there is sufficient water in tank and ‘Underground Tank Empty’ which indicates no water in underground tank. Third one is again common anode which provides +5V.

Now we will see how the sensors work. Water is conducting as salts are present in normal water. In tanks, Common anode is kept at the base which provides 5V, if any sensor gets immersed in water, due to conduction in water it becomes high. If water level is below a sensor it will be open circuited and we have to take good care of it as it is not grounded and some ICs take open circuit as high which is a practical problem because we want to take this condition as low. This problem can be solved by first inverting all the inputs using transistors (as inverters) and then again inverting them implementing the logic using IC’s.

brass screw sensors

Another metal contact sensor covered
by plastic case

The sensors fixed at various levels are shown in the image below:

sensors in an overhead tank

Water level in no case will go above O.T.F. and when it goes below O.T.E. the tank is considerd empty.
Water level can go above U.T.S.. Pump will switch on automatically only when water level in underground tank is above U.T.S. and in overhead tank below O.T.E. and can remain on till it reaches U.T.E. or overhead tank becomes full, whichever comes first.
Pump will remain off if overhead tank is full or underground tank is empty.
In rest all combinations of possible conditions, pump will remain in its previous state i.e. if it was off it will remain off and if on then it will remain on.

We will now see the system as a digital circuit and for that we need to analyse it in the terms of ones and zeroes. So let us consider a few conditions to make this more clear

Underground Tank empty :- U.T.E. is 0 U.T.S is 0
Sufficient water in U.T. :- U.T.E. is 1 U.T.S is 1
Water level between U.T.S. and U.T.E. :- U.T.E is 1 U.T.S. is 0
Overhead Tank empty :- O.T.E. is 0 O.T.F is 0
Overhead Tank full :- O.T.E. is 1 O.T.F is 1
Water level between O.T.S.and O.T.E. :- O.T.E is 1 O.T.S. is 0

We have 4 inputs: U.T.E., U.T.S., O.T.E. and O.T.F. Let us consider the truth table so that we determine all possible conditions:

P is the output to the pump's relay.

U.T.E.	U.T.S.	O.T.E.	O.T.F	Condition	P
0	0	0	0	U.T. & O.T. empty	0
0	0	0	1	Not Possible	X
0	0	1	0	U.T. empty, O.T. neither full nor empty	0
0	0	1	1	U.T. empty, O.T. full	0
0	1	0	0	Not Possible	X
0	1	0	1	Not Possible	X
0	1	1	0	Not Possible	X
0	1	1	1	Not Possible	X
1	0	0	0	U.T. neither full nor empty, O.T. empty	Previous state
1	0	0	1	Not Possible	X
1	0	1	0	U.T. neither full nor empty, O.T. neither full nor empty	Previous state
1	0	1	1	U.T. neither full nor empty, O.T. full	0
1	1	0	0	U.T. full, O.T. empty	1
1	1	0	1	Not Possible	X
1	1	1	0	U.T. full, O.T. neither full nor empty	Previous state
1	1	1	1	U.T. full, O.T. full	0

In a few conditions, output ‘P’ takes its previous state as we can see in the above truth table.
This can be explained by taking the following example:

U.T.E.	U.T.S.	O.T.E.	O.T.F.
1	1	1	0

There is sufficient water in the underground tank and in overhead tank water level is between O.T.E. and O.T.F. i.e. overhead tank is neither full nor empty. This situation can arise in two cases:
1) Let us assume that overhead tank is full so the pump is off and P=0. Now with consumption of water, it will drop below O.T.F. and the above illustrated condition will occur.We cannot keep the pump on because if we do so, process of pump on and off will occur too fast (approximately after every minute or so). As the water level will lose contact with O.T.F. sensor, pump will switch on and now the tank will get full too soon and the pump will switch off. This fast occurring cycle can damage the water pump. Hence, O.T.E. has its own significance that the pump should switch on only when it is low.

2) Now assume the overhead tank to be empty i.e. O.T.E. low. Pump will switch on and the tank will start filling. Now the same condition will again occur and we cannot keep the pump off as we are required to fill the tank till brim, once the pump is on.

So, in certain conditions the ‘P’ has to take its own previous value that if it was off it should be off and if it was on it should be the same.

For ‘P’ to have its own previous value in some states, we will have to give feedback i.e. our circuit will have one more input P(n) and output from it will be P(n+1).And so we have the final truth table:

P(n)	U.T.E.	U.T.S.	O.T.E.	O.T.F.	P(n+1)
0	0	0	0	0	0
0	0	0	0	1	X
0	0	0	1	0	0
0	0	0	1	1	0
0	0	1	0	0	X
0	0	1	0	1	X
0	0	1	1	0	X
0	0	1	1	1	X
0	1	0	0	0	0=P(n)
0	1	0	0	1	X
0	1	0	1	0	0= P(n)
0	1	0	1	1	0
0	1	1	0	0	1
0	1	1	0	1	X
0	1	1	1	0	0=P(n)
0	1	1	1	1	0
1	0	0	0	0	0
1	0	0	0	1	X
1	0	0	1	0	0
1	0	0	1	1	0
1	0	1	0	0	X
1	0	1	0	1	X
1	0	1	1	0	X
1	0	1	1	1	X
1	1	0	0	0	1=P(n)
1	1	0	0	1	X
1	1	0	1	0	1=P(n)
1	1	0	1	1	0
1	1	1	0	0	1
1	1	1	0	1	X
1	1	1	1	0	1=P(n)
1	1	1	1	1	0

Now we can deduce an expression from the table by having the minterms that produce 1.

Let P(n)=A, U.T.E.=B, U.T.S.=C, O.T.E.=D, O.T.F.=E, P(n+1)=Z for simplicity in calculations.

Z=A’BCD’E’+ABC’D’E’+ABC’DE’ +ABCD’E’+ABCDE’

=A’BCD’E’ + ABC’E’(D + D’) + ABCE’(D + D’)

=A’BCD’E’ + ABC’E’ + ABCE’

=A’BCD’E’ + ABE’(C + C’)

=A’BCD’E’ + ABE’

=BE’(A’CD’ + A)

=BE’(A + CD’)(A + A’)

=ABE’+ BCD’E’

So we have the final expression

P(n+1)= P(n).UTE.OTF’ + UTE.UTS.OTE’.OTF’

We can have a simple circuit to implement the above expression:

Circuit with pump in on state

Circuit with pump in off state

Connecting LEDs is helpful so that the user can determine the status of overhead tank and underground tank. This system is very convenient and requires no human intervention.

SEMI-AUTOMATIC PUMP DRIVER SYSTEM

In summers, in scarce water conditions, suppose the water level is maintained between U.T.S. and U.T.E. and overhead tank is completely empty. It will not work till the water level is above U.T.S. In this case automatic system fails and user will switch the pump on manually i.e. by switching to manual mode. Now, in no case pump should be on when water level is below U.T.E. (pump would be running dry) and when O.T.F. is high (overhead tank full). In manual mode nothing would be taken care of so Semi-automatic Pump Driver System comes into picture.

User will only have to switch on the pump and it will intelligently switch it off. As mentioned earlier two conditions are taken care of:

U.T.E. should not be low.
O.T.F should not be high

So the system requires only 3 inputs: U.T.E., O.T.F and user’s input U.

We omit the sensors O.T.E. and U.T.S because they are not required and hence we consider the following diagram:

As we have 3 inputs, out of which one will be from the user. User will just press a push to on button for switching on the pump so just a trigger will be given and for converting it to a sustained input we will again require feedback. It will become more clear from the truth table.

U(n)	U.T.E.	O.T.F.	U(n+1)	P
0	0	0	0	0
0	0	1	0	0
0	1	0	0	0
0	1	1	0	0
1	0	0	0	0
1	0	1	0	0
1	1	0	1	1
1	1	1	0	0

We get a 1 for P and U(n+1) only when U.T.E. is high, OTF is low and user wishes to switch on the pump i.e U(n) is high.

So we can have the expression from the truth table.

P= UTE.U(n).OTF’

For the above expression we can have the following circuit:

Circuit with pump on

Circuit with pump off

As only two inputs (U.T.E. and O.T.F.) amongst the four in automatic pump driver are used here, we can make a system which has both modes automatic as well as semi-automatic. Infact we can add a manual mode too in the system. This will be a complete system and will give no problems.

SEMI/FULLY AUTOMATIC WATER LEVEL INDICATOR AND CONTROLLER

We can make this by combining all the three modes: automatic, semi-automatic and manual. This can be done by giving a 3-way switch on relay’s input i.e. relay will take input from the mode, which user has selected.

The above circuit seems to be complex but is not actually. The relay has been connected to a 3-way switch i.e. it can get three inputs from three systems. The system requires the same number of sensors as in automatic pump driver system. The circuit in red outline is of automatic mode, in green outline is of semi-automatic mode and in black is of manual mode.

The latter two we have studied. In manual mode switching the pump on and off is user’s wish so no input is taken in the circuit. Two inverter gates are put to for delay so that feedback works. If user pushes to on once, the ouput is fed back to the input and pump remains on. If user pushes to switch off, output is grounded and logic ‘0’ is fed to switching on input and the pump stops.

So, we have the circuit:

Considering all the above three systems, some users may only want to prevent overhead tank overflow and for that we can make a much simpler system.

OVERHEAD TANK OVERFLOW GUARD

This system will prevent tank overflow and the system will have only two inputs for monitoring basis: O.T.F. and U(n). This is the simplest system among all and covers the most important function. Circuit of the system will be:

Installing an appropriate system from all the above systems will reduce human efforts and will help to manage and conserve water well.

PLOTTING 2-D GRAPHS USING MATLAB

2011-12-08T03:21:00.000-08:00

2-D graphs in MATLAB (7.10.0 R-2010a) can be easily plotted using ‘plot ( )’ function. I am not describing the details of MATLAB and using plot function.

An example of plotting a 2-D graph (sine curve):

x=0:0.01:2*pi;

y=sin(x);

plot(x,y);

An example of plotting two graphs simultaneously:

x=0:0.01:2*pi;

y=sin(x);

z=cos(x);

plot(x,y);

hold on

plot(x,z,'--r'); %’--r’plots dashed red colored graph
hold off

Title, x-axis label, y-axis label, legend, arrow can be added using the option ‘Insert’ in figure window or using the Plot Edit Toolbar.

Grid lines can also be added using property editor-axes (go to edit option and then click axes properties) or by simply checking the edit plot option in tools and then right clicking on graph and checking the grid option. In the figure grid lines are added for only y-axis.

Legends can be edited by double clicking on them (initially you will see data1 and data2 written). Also properties of it can be edited using the property editor.

I have changed the x-limits to 8(explained later) so that the legend does not hide a part of graph. This is not necessary, but doing this makes the graph look neat and realizable at every point.

Edit Plot option in ‘Tools’ can be useful to avoid certain commands or alterations in commands and also properties of the figure, graph paper, graph can be changed.

1) FIGURE PROPERTIES

Check the Edit Plot option in tools and then left-click outside the graph i.e. the area which is purple in the figure. This gets the rectangle formed by 8 square bullets at the outermost of the figure. Now right click in the same area and you will get four options: Color, Close Figure, Show Property Editor (by which you can give the figure window a desired name and get the color options), Show M-Code.

2) GRAPH PAPER PROPERTIES

Edit Plot option being checked; click inside the graph paper and not on the graph drawn such that the eight rectangular bullets appear on the boundary of graph paper as shown in figure and then right click.

Add Data option is a useful one and is discussed later.

Color option allows you to change the color of graph paper (here I have changed it to light green).

Show Property Editor option opens property editor-axes as shown in figure. From here you can give labels, set limits of the axes (here set to 8), grids for respective axis can be added and many more properties can be changed.

3) GRAPH PROPERTIES

In order to study graph properties we take a different example:

x=0:0.1:2*pi;

y=sin(x);

plot(x,y);

To edit the graph or plot we follow the same procedure i.e. check the edit plot option and now click on the graph or plot and nowhere else and the rectangular bullets will appear on the graph and now right click it.

Option color allows to change the color of plot, Line Style (way of joining points or plotting) can be set to solid, dash, dot, dash-dot, none.

In the figure shown below color of graph has been changed to black and Line Style is kept solid.

Line width is thickness of the graph and 'Marker' is another beautiful option which can make the graph look better, and its size can be adjusted by 'Marker Size'.

In the figure drawn below marker selected is ‘*’ as it can be seen checked and various types of it can be selected.

These options can be added by commands also and it is important to know them. We can edit the graph from the figure window but if multiple graphs are plotted like in case of 3-D figure where 200 or more graphs can be plotted on the same graph paper editing is not possible as we will have to select them one by one and do the required changes. Commands are convenient in this case as they can be put in the loop and the required condition will be applied to all the graphs. This you can evident from my next post.

Show Property Editor opens Property Editor-Lineseries window and similar options of Line style, Line width, Marker, Marker Size are available and we can opt for different Line Style color and different marker color which we earlier couldn’t do.

X data source and Y data source can be also specified by just putting the expression in the respective column. In the figure shown below Ydata source has been put ‘cos(x).*exp(-0.2*x)’ and x dat source auto and the resultant graph is shown.

In the Edit Plot mode, in all the possible three domains: figure, graph paper and graph explained earlier, Property Editor function is the best function as you can access all possible options for editing and many additional ones too, which are useful like different color can be filled in markers (closed), outline can be of different color and the graph can be given a third color. In the edited damped sine the marker is filled with red, outlined with blue and graph is dashed black. A simple graph of damped sine can be drawn simply by defining x vector and putting y= sin(x).*exp(-0.2*x) and can be made presentable by editing.

graph without editing

same graph edited using various property editors

2-D GRAPH TYPES

Many types of graphs can be plotted using MATLAB : bar graphs, pie charts etc.

I will explain the useful graph types in brief, so that they can be used for basic work. Let us assume the following data of a company:

Year	2005	2006	2007	2008	2009	2010
Company A profit(in crores)	500.43	562.62	357.81	597.39	624.61	731.98

Now if we simply plot the data, the graph is not very much understandable, as shown

The x-axis is plotted with step size 0.5 i.e. 2005, 2005.5, 2006… In order to change it to one go to Property Editor-Axes as shown in above figure. Click the ‘Ticks..’ option, ‘edit axes ticks’ window will pop up as shown and then check the ‘Step by’ option and put 1 in the text box and click apply.

Graph can be made presentable by using bar graphs.

BAR GRAPHS

For the above plotted graph or the normal plot or Lineseries graph, go to Property Editor-Axes and change the Plot Type option to bar as shown in the figure 2.

Also the Plot Type can be changed using 'Add Data' option which I earlier mentioned in graph paper properties and this option can be selected by Plot Browser also.

Direct command bar(var1,var2) can be used to plot bar graphs. Commands can also be used to plot a certain color bar graph, line width can also be specified by commands.

figure1 bar graph

But still it is not presentable. We can again follow the plot editing techniques using ‘Edit Plot’ option in the three domains. But this time, Property Editor in the third domain will be Property Editor-Barseries as shown in figure 2 and after editing the graph will appear as in figure shown below. Bar width and color can be changed by respective options, in Property Editor-Barseries.

figure-2 bar graph

Data of the corresponding bar can be written above the respective bar with the help of Text Box and properties of it can also be edited by double-clicking on it. Property Editor-Text box will open up and properties can be modified.

I plotted another dashed lineseries red graph to make it look better. However, it is not necessary. The final edited graph, may look like shown below:

AREA GRAPH

It fills the area under lineseries graph with the color of graph and then the outline or plot color can be changed. Change the Plot Type to Area after plotting the graph. area(var1,var2) command can also be used to plot the graph.

STAIR AND STEM GRAPH

Commands stairs(x), stairs(x,y) etc. can be used for stairs and stem(x), stem(x,y) can be used for plotting stem graph. These can also be selected from the Plot Type or the Plot catalog and editing can be done in edit plot mode.

PIE CHARTS

Pie charts are used for one variable. Consider in a survey if 52% of students opt engineering, 14% medical,18% commerce and remaining 16% other fields and we are required to draw a pie chart then following can be done:

a=[52 14 18 16 ]; %declare the vector with data to be plotted

pie(a) % forms a pie chart for data a

Each patch can be edited e.g color, outline etc. and a patch can be separated out by defining another vector whose dimensions are equal to that of vector of data. If we are required to separate other fields students patch. Then 4^th value should be put1and rest zero,

c=[0 0 0 1];

pie(s,c)

Pie charts can also be made from the Plot Catalog from Figure palette or from Plot Type.

3-D graphs, 3-D pie charts, 3-D bar graphs, 3-D figures can also be drawn using MATLAB which I will explain in my next post.

FLOWING WATER INDICATOR

2011-09-28T10:32:00.001-07:00

Submersible water pumps in underground water tanks are commonly used for filling overhead tanks. Sometimes, the water pump may run dry in case of low water level. This may cause an internal damage to the pump. To avoid this an fully/semi-automatic pump driver system and water level indicator can be used which will switch on the pump if water-level of the overhead tank is below a particular level and if there is adequate water in the underground tank. It will also switch it off or keep it switched off, if the overhead tank is full or in case of low water level in the underground tank. But this method is a bit costly and obviously it is fully automatic and is the best solution. But I made something which I think is the cheapest solution to the problem i.e. FLOWING WATER/WATER STREAM INDICATOR.

If the pump will run dry, there will be no water in the pipe through which the overhead tank fills. This condition can be detected by a simple electrical circuit. Impure water is a good conductor of electricity and I used this principle.

In the above circuit LED glows when water is flowing and switch is closed. I used a 16 V source for this circuit and adjusted potentiometer to around 1.66 k(explained later) so that voltage drop across LED is less than 10V. As flowing water resistance is in series, value of the components may vary which can be easily calculated.

SENSORS FITTED ON A
THERMOCOL BLOCK

I used a waste thermocol block of dimensions about 20cm x 8cm x 8cm (according to my plastic overhead tank and the pipe in it as shown in picture) for getting the sensors(conductors) fixed just below the pipe. So you may use a block (water resistant) of different dimensions for fitting the sensors/conductors.

I used two 2.5” brass screws (as they don’t rust) as my sensors and fitted them 3cm apart from each other along the axial line of pipe and tied two ends of wire on the heads of both the screws.

The length of the wire tied to both the screw heads was 30 feet in this case and this can vary according to the place where you want to fix the LED and LED can be fitted anywhere inside your home or near the motor switch.

CALCULATION OF VARIOUS PARAMETERS

Value of resistance in series(R1) will vary according to the length of wire, type and pressure of water.

In the circuit used above, replace 10k pot and led with a multimeter i.e. connect a multimeter with the sensors under flowing water and with full length of wire as shown in the circuit:

Set the multimeter to voltage measuring mode and get the reading. It will give us the value of open circuit voltage which would be approximately V(16V in this case) and then set the multimeter to current measuring mode and get the short circuit current reading.It will be a few milli-amperes due to the flowing water resistance.In my case it was around 4-5mA and so the resistance offered by water was approximately16V/5mA=3.2k .Now come back to the original circuit with LED. We need to limit the forward voltage of led to 5-10V. I wanted it to be 6V which can be monitored by connecting a voltmeter(multimeter set involtage mode) in parallel with the led.Keep on adjusting the potentiometer till you get 6V or desired forward voltage across LED.Current will decrease accordingly which we dont need to worry about as it would be less than 5mA and forward current limit of a LED is 20mA. Set the multimeter to resistance mode and measure the set potentiometer resistance(R2).The current can be calculated by a simple kvl equation:

V-I(R1+R2)-V1=0

V=source voltage

I=series current

R1= resistance offered by water stream

R2=series resistance(10 k pot. which was set)

For my project I substituted V=16, R1=3.2k, V1=6V and R2=1.66k

16-I(3.2k+1.66k)-6=0

I=2.05mA

This circuit can be used in any case where you need to detect flowing water. Rain water can be detected by replacing both the screws and using sensor which works for rain drops. Sensor can be made by etching a pcb which look likes below :

But now the values of the components will change because even a drop of water will glow the led.

IMAGES OF WATER STREAM DETECTOR:

(view enlarged images by clicking on them)

CIRCUIT TESTING

BLOCK FITTED IN OVERHEAD TANK

TWO NUT-BOLTS FITTED VERTICALLY
TO FIX THE BLOCK

TWO NUT-BOLTS FITTED HORIZONTALLY
FOR THE SAME

LED FITTED NEAR MOTOR SWITCH

WATER STREAM FALLING ON
BOTH SCREWS

FULL VIEW OF THE SYSTEM
WITH OVERHEAD TANK