...:: قريبــا ::......:: قريبــا ::......:: قريبــا ::......:: قريبــا ::...

يا طـالـب المـجــد فـي عجــور مــورده =عـــذب مـعـيــن يـروّي غــلــة فـيـنـــــا=شــــم الأنــــــوف أبــاة دام عـــزهــــــم =هـــم الأوائــل إن نــادى مـنــاديــــــنــــا=تـفـوح يـا بـاقـة الأزهـــار فـي وطـنــي =فــوح الأريـــج ونـفـح الطيــب يغـريـنـا كلمة الإدارة


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العودة   منتديات عجور > المنتدى العلمي > قسم الهندسة
 
 

قسم الهندسة الهندسة المعمارية,المدنية,الميكانيكية,الكهربائية ,الزراعية وغيرها

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قديم 08-03-2011, 07:27 PM   #1
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
Mmi مشاريع هندسيه لطلاب الهندسه الكهربائيه والالكترونيه

مشاريع هندسيه لطلاب الهندسه الكهربائيه والالكترونيه
Building a computer controlled radio transmitter


Building a computer controlled radio transmitter


How would you like to send text messages to your friends without wires, and without an Internet connection, and without paying monthly fees?
In this project we will build a very simple radio transmitter that you attach to a serial port on your computer. The computer then runs a free program that converts words you type into radio signals that are decoded by another computer, using a cheap radio receiver, and a sound card.
With a little study, you don't even need the second computer, since the radio signals are in Morse code, which anyone can learn to decode in their head with a little practice. It also comes in handy as a secret ********, or as a way to send long distance messages with a pocket mirror



Click on photo for a larger picture

The computer controlled transmitter needs these parts: (We carry most of the necessary parts in our catalog.)



A one megahertz oscillator
You can use other frequencies if you have a radio that can receive them. We carry this item in our catalog.

A serial port connector
We use a 9 pin RS232 connector. You can take apart an old serial cable, or buy a new connector from an electronics or computer store. We carry this item in our catalog.

Some insulated wire for an antenna
Just about any kind of wire will do, the longer the better.

An alligator test lead
This is a piece of wire with alligator clips at each end. We carry this item in our catalog.


For our first transmitter, we will connect the parts with alligator clips. This lets us quickly change frequencies by replacing the 1 megahertz oscillator with an oscillator with a different frequency. Later we will show a version made with a socket for the oscillator, a printed circuit board, and a light emitting diode that flashes morse code along with the oscillator



Click on photo for a larger picture

The first step is to cut the test lead in half. In these photos I have cut two test leads, one red and one black, to make it easier to see where the connections go. But unless you are making two transmitters (your friend wants to send messages back, doesn't she?) you can just use one test lead (cut into two pieces).
Remove a little insulation from the cut ends of the wire, and solder one of the cut ends to pin 5 and the other to pin 4.




__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
قديم 08-03-2011, 07:27 PM   #2
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
افتراضي

Pin 5 of the serial port connector (the black wire in the photo) connects to the ground pin of the oscillator. Pin 4 of the serial port connector goes to the power pin of the oscillator. The drawing shows the transmitter from the top (pins pointing down). The photo below shows the oscillator upside down, with the pins facing up



The green alligator clip attaches to the antenna, which can be any long wire. It is attached to the output pin of the oscillator. The remaining pin of the oscillator (the one nearest the sharp corner) is not used.
Your Computer Controlled Transmitter is now complete!

Controlling the transmitter

To send a message, we now need a computer program that can convert what we type into Morse code, and turn the oscillator on and off in the short and long pulses (dots and dashes) that are required.
A program to do that (for the Windows operating system) can be downloaded by clicking here. Save the ZIP file on your computer, use a ZIP file decompressor to unpack it, and then double-click on the resulting MorseCode.exe to start running it.




[IMG]Once the program is running, you will see a window like the one above. Type something in the window (such as "Hello there!") and then select the Transmit item in the Radio menu. Your transmitter is now sending your message.[/IMG]



can select how fast the message is sent by using the Speed menu.
You can control which serial port to use through the Com Port menu




The Radio menu has three selections we have not discussed yet. The AM Low Tone selection sets the tone you hear in the AM radio to 500 hertz. The AM High Tone selection sets the tone to 1,000 hertz. The CW selection is only for short-wave radios that have an SSB or CW mode. This selection does not modulate the radio signal, so an AM radio will just hear clicks. This selection allows the signal to be heard farther away, but requires a more expensive short-wave receiver. I have used the



Grundig YB 400PE radio with great success. It usually sells for about $150.00



you are a computer programmer, and would like to look at the source code for this program, you can download it here. There is also a much simpler, command-line version of the program here.


Receiving the code with a computer


Until you have learned to decipher Morse code in your head, you will want to have a computer do it for you.
There are many free programs floating around the Web that will do this for you. One such program can be downloaded here. I won't go into its operation (since I didn't write it), but it has a Help menu, and it is fairly straightforward to use. You will need an audio cable to connect the radio's earphone jack to the computer's sound card input jack, but that is all the hardware required.



You can see it working in the screen shot above, decoding our endless loop of "hello there".
__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
قديم 08-03-2011, 07:28 PM   #3
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
افتراضي

How does it do that?


Most of the important concepts for this project have been covered in other sections of this chapter.
The computer provides power to the oscillator through the DTR pin of the serial port. The program turns the DTR signal on and off, which causes the oscillator to turn on and off in return.
To make the signal audible in a cheap AM radio, the computer turns the power to the oscillator on and off 1,000 times per second while sending the dots and dashes of the code, and leaves it off in between the dots or dashes. This modulates the radio signal at a frequency your ears can hear. In AM Low Tone the audio frequency is 500 times per second.
In the CW mode (CW stands for Continuous Wave), the computer does not modulate the radio signal. It just turns on the oscillator long enough for the dot or dash to be sent. In this case, the receiver does the work of converting the signal into an audible tone your ears can hear, by using a circuit called a beat frequency oscillator. Your short-wave radio may have a switch labelled BFO, or SSB, or CW that allows this circuit to operate.

Some nicer packaging


The computer program turns on DTR and also another signal called RTS, while sending the dots and dashes. In the version of the transmitter shown below, we have mounted a 14 pin socket to a general purpose circuit board from Radio Shack, and plugged the oscillator into that. A blue light emitting diode is connected to the RTS pin of the serial port connector (pin 7). The LED flashes Morse code along with the oscillator, making an eye-catching project.




The serial port connector is wedged onto the printed circuit board by placing the board between the pins



The wires that connect the serial port connector to the oscillator and the LED also serve to hold the connector onto the printed circuit board.
The antenna in this case is a 6 inch long wire. In CW mode, this wire is all that is needed to receive the signal anywhere in the house. A longer antenna will allow the whole block to receive the signal.
By replacing the 1 megahertz oscillator with a 28.322 megahertz oscillator, and connecting the transmitter to a large amateur radio antenna (10 meter beam), I was able to send signals from California to Texas. To do that, you will want to get an amateur radio license.
__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
قديم 08-03-2011, 07:28 PM   #4
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
افتراضي

A simple laser communicator
How would you like to talk over a laser beam? In about 15 minutes you can set up your own laser communication system, using cheap laser pen pointers and a few parts from Radio Shack.
For the transmitter you will need:




A laser pen pointer. You can get one for $10 from our catalog.



A battery holder that holds the same number of batteries as the laser pointer (often 3 cells). The batteries can be any size, but they must be the same voltage as the laser batteries. You may need to get one that holds two cells, and another that holds one cell, and wire them together in series. Radio Shack has a decent selection.



A transistor radio. Later we will use a microphone and an amplifier (Radio Shack #33-1067 and #277-1008), but at first we will send your favorite radio station over the laser beam.



An earphone jack that will fit your transistor radio (Radio Shack #42-2434).



A transformer of the type known as an audio output transformer. It consists of an 8 ohm coil and a 1000 ohm coil. The one I used is the Radio Shack #273-1380. We now carry them in our catalog.



Some clip leads (wires with alligator clips on the ends) to put it all together. At least one of the clip leads should be the type with a long slender point (Radio Shack #278-016, #270-372, or #270-334), to connect to the inside of the laser pointer. You can substitute regular wire and solder if you like, but the clip leads are fast and simple. Radio Shack has a wide selection of clip leads (such as ##270-378).



A two-lead bicolor light emitting diode, to protect the laser from high voltage spikes.




For the receiver you will need:




A small solar cell (such as Radio Shack #276-124). You may have to solder your own wires to it if it doesn't come with wires attached.

A microphone jack that will fit the phono input of your stereo (Radio Shack #42-2434 or ##42-2457). Instead of a stereo, you can use the small amplifiers that Radio Shack sells (#277-1008).


It may be hard to find a battery holder that holds three batteries. You can use two battery holders (one that holds two batteries, and one that holds a single battery) and connect them in series.
Remove any batteries from the laser.
Connect a clip lead to the inside of the laser pointer where the battery touched. Usually there is a small spring to which you can attach the clip lead. The other end of the battery usually connects to the case of the laser. Since there are many different styles of laser pointer, you may have to experiment with clip lead placement to get the laser to work with the new external battery pack. You may also have to hold down the laser's push button switch by wrapping a rubber band or some wire around it. Test the connection before you attach the transformer, to make sure the laser works with the new battery pack. If it doesn't light, try reversing the battery. Battery reversal will not harm the laser.
Connect the 1,000 ohm side of the transformer between the battery and the laser. The 1,000 ohm side of the transformer has three wires coming from it. We only use the outside two wires. The inside wire is called a center tap and we do not use it in this circuit.
Connect the bicolor light emitting diode to the two outside wires of the transformer on the 1,000 ohm side. We are using this part (the bicolor LED) as a protection device to prevent the laser from getting high voltage spikes from the transformer. We didn't need to do this with the old-style lasers that had protection circuits built into them, but there are a lot of lasers being sold lately that have no protection, and need the bicolor LED to absorb any extra high voltage the transformer may produce when it is connected or disconnected. If you see the LED flash when you connect the battery, you will be seeing it absorb a high voltage spike that might have otherwise damaged the laser.
Test the laser by attaching the battery. The laser should operate normally at this point.
Connect the earphone jack to the 8 ohm side of the transformer. The schematic of the transmitter looks like this




The transformer modulates the power going to the laser. The signal from the radio is added to and subtracted from the battery power, and the laser gets brighter and dimmer along with the volume of the music or voice in the signal.
The receiver is the simplest part. You simply connect the solar cell to the microphone jack, and plug it into the amplifier or stereo phono input. It does not matter which way the wires are connected to the solar cell.
Here is the schematic of the receiver:

__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
قديم 08-03-2011, 07:29 PM   #5
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
افتراضي

Setup and testing


Make sure the transistor radio is turned off, and the laser is on. Plug the earphone jack of the laser into the earphone socket of the radio.
Connect the solar cell to the amplifier or stereo, and turn the volume up until you hear a hissing noise, then turn it down slightly until the hiss isn't noticeable. The volume control should be fairly high, corresponding to an ear splitting level if it was playing music.
Aim the laser across the room so it hits the solar cell. You might hear clicks or pops coming from the stereo or amplifier as the laser beam passes over the solar cell. This indicates that everything is working fine at this point



Click on photo for larger picture
Now carefully turn on the radio and slowly adjust the volume until you hear the radio station voices or music coming from the amplifier across the room. The radio should be just audible if the earphone jack is pulled out, not loud. If you can't hear the sound from the amplifier across the room, make sure the laser is shining on the solar cell, then try increasing the volume of the amplifier before you increase the volume of the radio.
At this point you should be hearing the radio station coming in loud and clear in the amplifier across the room. Put your hand in front of the laser beam to break the connection, and notice that the music stops. Wiggle your fingers in the beam and listen to the music get chopped up by your fingers. Your laser communicator is ready for the next step.
To send your voice over the laser beam, you simply replace the transistor radio with a microphone and amplifier. Radio Shack sells small amplifiers (about the same size as the transistor radio) that have sockets for microphones and earphones. You can also use another stereo system, but be very careful with the volume control to prevent damage to the laser.



Using a disassembled laser pointer.


For this project we have removed the laser assembly from a small $10.00 laser pointer. The power supply circuit is the green board attached to the brass laser head. We carry similar laser pointers in our catalog that are easily disassembled for this project.
The laser below has voltage spike protection on the circuit board. The one you get may not have this, and so you will want to put a bicolor LED across the transformer like we did in the previous version



The power supply circuit came conveniently marked with a plus and a minus next to two holes in the board. We solder the black negative lead from the battery clip to the hole marked minus. We solder one of the 1000 ohm coil leads to the hole marked plus. We solder the red positive lead of the battery clip to the other lead from the 1000 ohm coil



The battery clip is attached to a 4.5 volt battery pack (not a 9 volt battery!). Since I didn't have a pack that takes 3 cells, I used one that takes 4 AA batteries, and I replaced one of the four batteries with a straight piece of bare wire.
That's it! We have a laser transmitter, in just a few minutes!


A new receiver


The solar cell receiver has some drawbacks. It is expensive (solar cells are a few dollars each), and fragile.
A cheaper, sturdier alternative is to use a cadmium sulphide photoresistor instead of the silicon photocell.
A cadmium sulphide photoresistor is shown below (magnified many times). It does not produce electricity from light the way the solar cell did. Instead, the light that falls on it changes its resistance to electricity.
If we connect a battery and a photoresistor together, they can act like the solar cell. As the intensity of the light changes, the amount of electricity output changes in response



The new receiver is very simple, and looks like this

__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
قديم 08-03-2011, 07:29 PM   #6
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
افتراضي

Super simple receivers


Using a super sensitive piezoelectric earphone (see our catalog), you can make a laser voice receiver that doesn't need any expensive amplifiers or power source. Just connect it to a small solar cell, as shown below



Click on photo for larger picture
Also in our catalog, we have tiny silicon solar cells that you can attach to a piezoelectric earphone with simple transparent tape, instead of soldering (which can be difficult to do on silicon solar cells).



a solar cell is too expensive or fragile, a cadmium-sulfide photoresistor can also be used. The earphone wires are connected across the photoresistor, and the battery is also connected across the same wires. The battery, the earphone, and the photoresistor are in parallel. A 220 ohm resistor is placed in series with the battery, to reduce power consumption, and prevent heating of the photoresistor



Click on photo for larger picture

Either of these earphone approaches has the nice feature of making the communication private. Only you can hear what is coming over the secret laser link.



How does it do that?


In all of the laser communicators on this page, the laser light is amplitude modulated. This simply means that the amount of light the laser emits varies over time.
To understand what is going on, it helps to consider how a loudspeaker makes sound. A loudspeaker is a paper cone attached to a coil of wire that sits in a magnetic field from a strong permanent magnet.
When an electric current flows in the loudspeaker coil, the coil becomes an electromagnet, and it moves toward or away from the permanent magnet. As it moves, the paper cone pushes on the air around it, compressing the air in front of it, and expanding the air behind it. Waves of compressed and expanded air travel to your ear, and cause your eardrum to move in time to the movements of the paper cone.
The laser communicator adds two components to the loudspeaker concept. We take the electrical signal that goes to the loudspeaker, and connect it instead to the laser, so the laser gets brighter and dimmer as the electric current varies. The second component is the receiver, which converts the light back into an electric current. This current varies in time with the first current, because the amount of light that it receives is varying in time.
This second electric current is used to move the paper cone of a loudspeaker, just as before. However, now the loudspeaker can be quite a distance away from the original electric current, without any wires connecting the two.
__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
قديم 08-03-2011, 07:30 PM   #7
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
افتراضي

Building a computer controlled laser

Although computers got their name from their ability to calculate, one of the main uses for computers today is in communications.
Our modern telephone system is a large collection of computers, communicating with one another by sending pulses of laser light through optical fibers



We can do the same thing at home. In this project, we will build a laser transmitter that the computer will control, sending data by flashing the laser on and off. But we will eliminate the optical fibers, and just send the light through the air, in what is called free space laser data transmission.
The computer controlled laser data transmitter needs these parts:

A pocket laser pointer
We carry this item in our catalog.

A serial port connector
We use a 9 pin RS232 connector. You can take apart an old serial cable, or buy a new connector from an electronics or computer store. We carry this item in our catalog.

An NPN transistor
Almost any type will do, such as the 2N4401 or 2N2222A. We carry this item in our catalog.

A 470 ohm resistor
This resistor will have color codes Yellow Purple Brown and Gold. We carry this item in our catalog.

A light emitting diode
We use a clear lensed red LED, but most any LED will do. We carry this item in our catalog.

A generic printed circuit board
This is not really required, but makes assembly easier. We use the Radio Shack 276-159B. We carry this item in our catalog.

An alligator test lead
This is a piece of wire with alligator clips at each end. We used half of a red one and half of a black one, to make it easy to describe how to connect them, but a single test lead cut in half will do nicely. It does not harm the laser to connect them wrong -- just switch them around if the laser doesn't light up. We carry this item in our catalog.

A nine volt battery clip
This is a clip on connector for a 9 volt battery. We carry this item in our catalog.

A spring-type clothes pin

A screw or nail about 2 inches long with a flat head

A small block of wood for a base

A nine volt battery

A bit of tape and glue to hold it all together


Modifications to the laser


We will not actually modify the laser, so it will be easy to undo the project and still have a working laser pointer. But we will be removing the batteries, taping down the ON switch, and inserting a small screw where the batteries were, to make it easy to connect the laser to the transmitter circuit we will build



With the batteries removed, we can look into the back end of the laser and see the small spring that normally connects to the negative terminal of the battery.
We can also see the switch that turns the laser on — it is the little black box with the red button.



To make it easier to connect the little spring to our circuit, we will wrap some tape around a small screw, and place the screw head against the spring. The tape will be wound around the screw until it makes a snug fit inside the laser, compressing the screw a little bit



Next, we use some tape to hold the ON button down. We will be turning the laser on and off with our circuit, so the button will no longer be used, and must remain in the ON position at all times


The computer will communicate with our circuit through its serial port. If your computer does not have a serial port, there are inexpensive USB serial ports you can buy that will connect easily to your computer and will work fine for our project



We will use a 9 pin female serial connector, attaching wires to pins 4 and 5 only. Those pins are the Data Terminal Ready pin (pin 4) and the Ground pin (pin 5



We will use a generic printed circuit board for this project, although all of the parts could simply be soldered together without it, or even connected with alligator test leads. But soldering the parts to a printed circuit board makes the project sturdy, and guarantees the parts will stay connected



One side of the board has copper foil printed on it. The other side of the board will have our components. The two sides of the board are called the solder side (where we do the soldering) and the component side (where the transistor, LED, and resistor will be).
When we hold the board up to the light, we can see the shadow of the copper foil showing through on the component side
__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
قديم 08-03-2011, 07:30 PM   #8
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
افتراضي



have drawn the outlines of the components onto the following picture of the circuit board. Some of the components seem to overlap in my drawing — this is because the parts will either be bent out of the way a little bit, or the leads will be left long, so one part will be higher than the others. You can choose to use either method of fitting the parts onto the board.
Solder the transistor onto the board first. With the flat side of the transistor facing the bottom of the page, the emitter, base, and collector wires will fit into three holes, and the wires soldered to the copper on the other side of the board.
Next, solder the LED onto the board by placing its leads through the proper holes and soldering them to the foil on the back side of the board. The LED has a flat side, which should face the left. The left lead is the cathode, and the right lead is the anode. The cathode will connect to the base lead (the middle lead) of the transistor, one hole down. The cathode lead is shorter than the anode lead.
Next solder the resistor in place. It will stand up straight, and the top lead will be bent over to go into the hole below the transistor's collector lead.
Cut off the excess leads on the solder side of the board, so it is neat and the leads don't accidentally bend onto one another.
Next solder the battery clip wires onto the board, as shown in the photo. I like to feed them through a large hole and tie a knot in them before I solder them to the board, to prevent the heavy battery from pulling the wires off the board if it falls. The negative (black) wire connects to the emitter lead of the transistor, one hole down. The red positive wire goes into the next unused hole to the right, just past the resistor.
Now we solder the wires from the 9 pin serial connector to the board. The wire from pin 4 goes in the hole below the black battery wire, so it connects to the emitter of the transistor and the negative terminal of the battery. The wire from pin 5 goes into the hole just above the anode lead from the LED, so it is connected to the LED anode.
Lastly, we cut the alligator test lead in half, and solder one half to the hole that leads to the red battery wire, and the other half to the hole that leads to the bottom lead of the resistor



In schematic form, the circuit looks pretty simple, since there are only four parts



We are now ready to connect all the parts together. We tape the laser to the clothes pin as shown in the photo, and glue the clothes pin to the block of wood. We insert the wedge shaped end of half of another clothes pin between the jaws of the first clothes pin. This arrangement makes it easy to make very small adjustments to the vertical angle of the laser beam, making aiming the laser much easier.
Connect the positive alligator test lead to the barrel of the laser, and the negative test lead to the pointed end of the screw. Connect the battery to the battery clip



Lastly, plug the serial connector into the serial port of the computer. The LED and the laser should both light up as soon as you do this. If they don't, then carefully check all of your connections, and make sure that you didn't accidentally bridge two of the copper foil traces together with solder.
If the LED lights up but the laser does not, check the connections, and also check that the button on the laser is firmly depressed.


Controlling the transmitter

To send a message, we now use the same computer program that we used in the Computer Controlled Radio Transmitter project to convert what we type into Morse code, and turn the laser on and off in dots and dashes.
There is one small difference in the setup, however. The laser is not directly powered by the serial port, as the radio transmitter was. The laser circuit has a transistor switch in it. The transistor inverts the signal. This means that when the serial port is turned on, the transistor turns the laser off. When the serial port turns off, the transistor turns the laser on. This is caused by the simple circuit we use. We could have used two transistors to prevent the inversion, but instead, we simply tell the computer program to invert the signals before it sends them. This is easier and cheaper than adding another transistor



receive the morse code signals, we can use a very simple receiver, made from a piezoelectric earphone and a small solar cell. (We carry this item in our catalog.)



You can also connect a phono plug to the solar cell instead of the earphone, and plug it into the sound card of another computer and use the same morse code receiving program as in the Computer Controlled Radio Transmitter project.

How does it do that?


Each of the four components in the circuit perform their own special task



The signal coming in from the serial port swings between 25 volts DC to -25 volts DC. The LED not only lights up to show that the signal got there, but because it is a diode, it cuts off the negative swings of the signal, so the transistor only sees a signal of 0 volts or 25 volts. (Most serial ports never actually go much higher than 12 volts, but the RS-232 specifications allow as much as 25 volts.)
The transistor is set up to act as a simple switch. It has three leads — the base, the emitter, and the collector. The emitter is connected to the negative side of the power supply, which is called ground, because it is often connected to the earth in electronics and radio circuits. The base is connected to the LED that lights up when the serial port signal is on.
When the base of the transistor sees the voltage go from 0 to anything more than about a volt, the transistor goes from the "off" state to the "on" state, allowing electrons to flow from the emitter to the collector.
The collector is connected to the 470 ohm resistor. This resistor is needed to prevent too much current from flowing into the laser, which would damage it.
We use a 470 ohm resistor because we want the current going through the laser to stay below 30 milliamperes. There is a simple rule for calculating how much resistance you need to limit the current. It is called Ohm's Law. It says that the current is equal to the voltage divided by the resistance:
amperes = volts ÷ ohms
We have 9 volts and 470 ohms, so 9 ÷ 470 is about 0.019 amperes, or 19 milliamperes (a milliampere is 1/1,000th of an ampere). This is enough to light the laser brightly, and yet well below the 30 milliampere limit that would damage the laser.
Finally, when the electrons flow from the emitter to the collector and then through the resistor, they get to the laser, and cause it to light up, sending a beam of light we can detect as far as a mile away at night, or across the street in the daytime.
__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
قديم 08-03-2011, 07:31 PM   #9
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
افتراضي

Fun with solderless breadboards



When building a circuit for the first time, it is often very useful to have a way to quickly change connections or parts placement.
In the early days of electronics, quick, temporary circuits were sometimes built on a piece of wood, similar to the boards that bread is sliced on. Building a first prototype came to be known as breadboarding.
Back when components like tubes and transformers were large and long wires were common, it was easy to solder and unsolder connections. Modern circuits, made with small transistors or many legged integrated circuits, are much harder to solder and especially to unsolder.
To make life easier, solderless breadboards were invented. These are blocks of plastic with holes into which wires can be inserted. The holes are connected electrically, so that wires stuck in the connected holes are also connected electrically.
The connected holes are arranged in rows, in groups of five, so that up to five parts can be quickly connected just by plugging their leads into connected holes in the breadboard. When you want to rearrange a circuit, just pull the wire or part out of the hole, and move it or replace it.



In the photo above, we have a complete radio, with an antenna coil, a tuning capacitor, a three-legged integrated circuit, a battery, and earphone, two resistors, and three capacitors. This radio is the Three Penny Radio kit from the Scitoys Catalog, which is usually soldered, using three pennies as convenient places to connect the various parts.
The three-penny radio needs these parts:

An antenna coil
You can wind one by hand, but in this project we use a much smaller coil with a ferrite rod inside, from our catalog.

An MK484-1 AM Radio Integrated Circuit
This is the heart of the radio. We carry it in our catalog.

A Piezoelectric earphone
Also in our catalog.

A tuning capacitor
We use a variable capacitor, from 0 to 160 microfarads. We have it in our catalog.

A 100,000 ohm resistor
This resistor will have four colored bands on it. The colors will be brown, black, yellow, and gold.

A 1,000 ohm resistor
This resistor will also have four colored bands on it. The colors will be brown, black, red, and gold.

A 0.01 microfarad capacitor
This capacitor will be marked something like ".01M" or "103".

Two 0.1 microfarad capacitors
These capacitors will be marked something like ".1M" or "104".

A 1.5 volt battery

A 1.5 volt battery holder

And, in this version:

A solderless breadboard
Also in our catalog.
and later:

A printed circuit board
Also in our catalog.




In the closer view, you can see that the parts we want to be electrically connected are plugged into one of the five holes marked A, B, C, D, or E, (or in this case, where we used the second half of the board, marked F, G, H, I and J) in rows marked 1 through 63.
Along each side of the breadboard are two strips of power supply rails, making it convenient to connect a battery when many parts need power. In our simple radio, only one part needs power, so it is convenient to simply plug the battery wires directly into the main circuit area.
The solderless breadboard is designed to accept the leads from parts such as resistors, integrated circuits, transistors, and other parts with round solid wire for leads. Some of the parts for the radio have thin, stranded wire that is not stiff enough to poke into the holes, or (like the variable capacitor) have flat strips of metal that are too big to fit into the holes.
For these parts, we solder their leads to pieces of wire cut from the leads of other parts, such as resistors or capacitors. Most such parts have leads that are longer than we needed anyway, so they will fit more snuggly onto the board with shorter leads. In the photo you can see that the antenna coil, the variable capacitor, and the piezoelectric earphone have wires soldered to their leads to make it easy to plug them into the breadboard



Having the holes arranged in a labeled grid is convenient for describing the parts layout. We can list each part, and the letter and number of each lead:

Antenna coil: J9 and G16

Tuning capacitor: F9 and F16 (only the two rightmost leads are used)

MK484 IC: H15, H16, and H17 (flat side facing row G)

100,000 ohm resistor( brown, black, yellow): I9 and J17

1,000 ohm resistor (brown, black, red): I17 and I20

0.01 microfarad capacitor (marked 103 or .01M): G9 and G15

0.1 microfarad capacitor (marked 104 or .1M): F15 and F17

0.1 microfarad capacitor (marked 104 or .1M): F17 and F22

Piezoelectric earphone: F20 and F22

Negative battery wire (black): J15

Positive battery wire (red): J20

This makes it very simple to build the circuit, and easy to double check all of the connections.


Making the circuit permanent


Solderless breadboards are great for building circuits the first time, and getting them to work, or experimenting with design changes. But when you get the circuit working the way you want it to work, you will want to copy it to a more permanent form, by soldering it onto a circuit board.
The printed circuit boards we carry in our catalog also have five holes that are electrically connected. The holes are grouped into 3 holes and 2 larger holes, to make it convenient to connect larger wires leading out from the board, for power connections and other external parts.
The radio shown below was built by a student as a first exercise in soldering




Here is the back side



It worked the first time!
__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
قديم 08-03-2011, 07:31 PM   #10
م .نبيل زبن
المؤسس
 
الصورة الرمزية م .نبيل زبن
 
تاريخ التسجيل: Sep 2010
الدولة: Jordan
المشاركات: 30,781
افتراضي

A digital thermometer

A digital thermometer



With the easy availability of inexpensive digital multimeters, and integrated circuit temperature sensors, it is now very easy to build a sensitive and accurate digital thermometer that can be used for many experiments around the house or in the amateur laboratory.
There are two tenperature sensors that make this particulary easy -- the LM34 and the LM35. These are callibrated in Fahrenheit and Celsius respectively, and when read by the meter, they produce ten millivolts per degree in their respective scales, so the meter can be directly read in temperatures, down to a tenth of a degree.
The digital thermometer needs these parts:



A multimeter. We chose a digital multimeter for accuracy and easy reading.
An LM34 integrated circuit temperature sensor for Fahrenheit.
An LM35 integrated circuit temperature sensor for Celsius.
A 180,000 ohm resistor
This resistor will have four colored bands on it. The colors will be brown, gray, yellow, and gold.
A nine volt battery
A nine volt battery clip
Two alligator test leads
Three long wires (optional)
Electrical tape or heat shrinkable tubing (optional)


We carry all the parts for the digital thermometer (except the battery and optional parts) in our catalog.




Shown above is a multimeter, set to read 0 to 2,000 millivolts (zero to two volts). Note that the dial switch is set to "2000 m".
It is currently reading 791 millivolts, which corresponds to 79.1 degrees Fahrenheit (since it is connected to the LM34 sensor



Above, we have placed an LM35 sensor on top of an ice cube, and the pool of water melted from the ice is reading 8.9 degrees Celsius. For this experiment we have simply connected alligator clips to two of the leads of the sensor, and wrapped the third lead with the red wire from the battery clip. No soldering, nothing fancy, and we have a digital thermometer in the time it takes to unwrap the meter and clip on the test leads



For a more permanent thermometer, we solder three long wires (about 5 feet is nice) to the three leads of an LM34 Fahrenheit sensor. Use three different colors, and note which ones are attached to which leads. We put a little electrical tape around the middle lead so it won't touch the other two, and then wrap the whole thing in electrical tape, or in this case, put it into a short length of heat shrinkable tubing, and warm it up so the tubing shrinks tightly around the whole assembly.
We made the wires long so that we can measure things inside boxes or behind doors. Five feet makes it easy to place the sensor end in the refrigerator or freezer, and have the meter stay outside where it is easy to measure. This arrangement is great for incubators for eggs, and terrariums, or (with proper waterproofing) aquariums.




At the other end of the long wires, we connect the battery clip and the resistor. Note that the wire colors help ensure that the right connections are made. In our case, the red wire from the battery clip is soldered to the brown and white striped wire, and the black wire from the battery clip is soldered to the brown wire. The brown wire is wrapped around one end of the resistor, and the blue wire is wrapped around the other end of the resistor. We can solder them later if we wish



In the photo above you can see how the heat shrinkable tubing makes a nice neat temperature probe, with only the top of the sensor peeking out of the shrunken tube.
The alligator test leads are attached to the resistor, and the other ends are clipped onto the meter probes, as shown in the photo below



?



The internal workings and theory of the LM34 integrated circuit temperature sensor is explained in minute detail by the manufacturer.




The circuit diagram is shown above. Briefly, there are two transistors in the center of the drawing. One has ten times the emitter area of the other. This means it has one tenth of the current density, since the same current is going through both transistors. This causes a voltage across the resistor R1 that is proportional to the absolute temperature, and is almost linear across the range we care about. The "almost" part is taken care of by a special circuit that straightens out the slightly curved graph of voltage versus temperature.
The amplifier at the top ensures that the voltage at the base of the left transistor (Q1) is proportional to absolute temperature (PTAT) by comparing the output of the two transistors.
The amplifer at the right converts absolute temperature (measured in Kelvin) into either Fahrenheit or Celsius, depending on the part (LM34 or LM35). The little circle with the "i" in it is a constant current source circuit.
The two resistors are calibrated in the factory to produce a highly accurate temperature sensor.
The integrated circuit has many transistors in it -- two in the middle, some in each amplifier, some in the constant current source, and some in the curvature compensation circuit. All of that is fit into the tiny package with three leads
__________________
الفاتحة لروح المرحوم اخي محمد زبن

هم عند قلبي بل وقلبي عندهم
وإذا بثثت الوجـــد بثوا وجدهم
ومعي أراهم لا أفارق قصدهـم
سعدت حظوظي إذ رضوني أبنهـم
والفخــــر لـي أنــــي إليهــــم أنسـبُ
م .نبيل زبن غير متواجد حالياً   رد مع اقتباس
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