PAGE 4 OF 4
WHAT IS A TRANSISTOR?
I have already explained that a hot "filament" glowing in a lightbulb is a RESISTOR, slowing down or 'resisting' electricity, and getting hot. Interestingly enough, the history of the TRANSISTOR starts off as a LIGH BULB as well! When Thomas EDISON was experimenting with the first light bulbs, he used hundreds of materials as the FILAMENT or HOT GLOWING WIRE that gets white hot, and gives off heat and light. He used Wood, Rice, Cotton, Carbon, etc. but always had a problem that as the white hot material 'BURNED" or glowed inside a glass bulb, it would give off black CARBON ( like coal ) that would coat the inside of the glass bulb and quickly block out all the light. Edison thought that by adding another WIRE and putting electricity on it, this would "ATTRACT" all the particles, and keep the inside of the light bulb clean. This was about 1880.
Much to his surprise, when Edison put an electrical meter on the third wire, he found that there was electricity coming out of it! He did not think this was very useful at the time, and although he showed this strange discovery to many others, he did nothing with it. The third wire was NOT connected to anything inside the bulb, so logically, there was no reason for it to have electricity on it. In fact, this was one of the first " VACUUM TUBES" or " RADIO TUBES" or "VALVES" ever made. Many years later, other people would USE this discovery to make Electrical TUBES that would only allow electricity to move in one direction ( a DIODE ), or that would AMPLIFY or make electricity stronger. ( DI is the same as BI or TWO, (( BI is from the Romans speaking LATIN, and DI is from the GREEKS )), so that a DI-ODE has two wires- a hot filament, and a "POST" wire that collects the electricity. A TRI-ODE (( TRI is 3)) has 3 wires, a hot burning filament, a post to collect the electricity, and a third wire, a "screen " in between, as described below ) Edison's first accidental tube was a DIODE, since electricity would travel from the hot, glowing wire, to the third wire, but no electricity would flow the other way. People associated this with a common water flapper valve, that allowed water to flow in only one direction, so that the common name for early tubes was a "Valve".
NOTE: It appears that there are 3 wires in a DI-ode and 4 wires in a TRI-ode, which
makes no sense. See the diagram below to see the logic !
How many wire ENDS are below the red line?
We now know that ELECTRONS, which are negative, will "boil" off of a hot wire, and are attracted to a POSITIVE wire, inside a glass bulb that has all the air removed -- a vacuum. This is just like magnets- South Pole and North Pole magnets ATTRACT, and North and North would repel each other- similarly, Positive wires attract Negative electricity. I am assuming that anyone reading this knows about ATOMS, which are made from the center PROTON, which is POSITIVE, and have an outer orbiting Electron, which is NEGATIVE. All substances on earth are made of atoms, starting with HYDROGEN, with ONE center PROTON, and ONE ELECTRON, then TWO PROTONS and TWO ELECTRONS is the ELEMENT HELIUM, then 3 would be LITHIUM, 4 would be BERYLLIUM, 5 is BORON, and 6 is CARBON, etc. Each element just gets more Protons, and more Electrons, and gets bigger and heavier.
If an atom gets extremely hot, the electrons spinning around the outside can get loose, and will shoot out off the atom if they are in a vacuum. If we use a 6 VOLT hot lightbulb wire inside a tube, it will "boil" off or give off electrons. If there is a POSITIVE charged plate or post in the tube, the NEGATIVE electrons will be attracted to it, and will fly across the empty vacuum space and hit the POSITIVE post.
What makes RADIO TUBES or Vacuum VALVES usefull is ADDING a SCREEN in between the Negative, hot wire that is making the electrons fly out, and the Positive "collector" plate. In order to get across the empty space, the electrons have to go through the holes in the screen. If you remember that NEGATIVE and NEGATIVE electrical charges REPEL each other, we can put in a tiny NEGATIVE charge, for example 5 VOLTS, on the screen, and all the NEGATIVE Electrons will be REPELLED by the screen, and NO electricity will flow from the hot wire to the Collector plate. But, if we turn off the electricity in the screen from 5 Volts to ZERO Volts, then there is no repelling force, and the Negative electrons will fly through the holes in the screen. Even more usefully, if there is 120 VOLTS from the hot filament wire to the Collector Plate, we can turn on and off 120 VOLTS with a tiny 5 VOLT ON / OFF amount of electricity! If you remember the picture of the RELAY, it turned ON and OFF 120 VOLTS with a tiny +5 VOLT electrical signal from a computer... - the TUBE, and the RELAY turn out to DO the same thing !
The TRI-ODE or 3-Wire TUBE above can turn ON and OFF LARGE amounts of electricity, by turning ON and OFF tiny amounts of electricity on the SCREEN in the middle. As Well, by putting in DIFFERENT amounts of electricity on the screen, for example 2.5 VOLTS, instead of 5 VOLTS, it can allow HALF the electricity to go through the screen, so that it can let 60 VOLTS go through. By putting in different amounts of electricity on the screen, you can get 20 VOLTS, 30 VOLTS, or 90 VOLTS flowing across the tube, all the way up to the full 120 VOLTS.... This is called AMPLIFYING the electricity, because a different small amount from ZERO Volts to 5 Volts, on the INPUT, or SCREEN, can be AMPLIFIED or INCREASED to make ZERO Volts to 120 VOLTS, on the OUTPUT.
HOW ARE TUBE AMPLIFIERS USED?
One of the first uses for a tube was to AMPLIFY tiny RADIO waves picked up on a wire ANTENNA, and make the tiny signal powerful enough to be heard on a large SPEAKER. The tiny electrical waves were put on the SCREEN in the center of the tube, and this turned on and off larger, stronger electricity that went to big speakers.
The next biggest popular use for tubes was in TELEVISIONS, where the tiny TV signals were brought in from the TV antenna, and amplified, and then put on the TV -- TUBE. Most people do not realize that the standard TV " IS " a TUBE! When you look at the front of a typical TV TUBE, you are looking at a sheet of steel, covering the entire front of the tube! I cut a piece of the steel out of a TV set that had the tube broken. You can see the size of the tiny section of screen by comparing it to the dime in the corner. From a distance, the sheet of steel looks solid.
You can see the metal screen has tiny holes in it, as shown in the enlarged section. The back of the TV tube has a hot glowing wire heater, just like a light bulb, and just like the radio tube above. At the front of the TV just behind the glass is the sheet of steel with tiny holes in it. The ELECTRONS, flying off the hot wire at the back of the TV, race towards the front of the TV because the steel plate at the front is 10,000 to 60,000 VOLTS more POSITIVE than the heater wire at the back. The NEGATIVE ELECTRONS are ATTRACTED to POSITIVE, and race to the front. Most of the electrons HIT the steel plate, but the ones that go through the tiny holes, hit RED, GREEN, and BLUE phosphor, a powder that gives off light -- just like the WHITE phosphor powder in long white flourescent tubes that are used in the ceilings in schools and libraries. The colored dots make up the picture that you see.
FINALLY, THE TRANSISTOR
The TRANSISTOR is called " SOLID STATE" since there are no moving parts, and there is no VACUUM involved. Instead of using a RELAY, or a VACUUM TUBE to turn on and off electricity, the Transistor uses SOLID ATOMS of ELEMENTS, like SILICON , to switch ON and OFF Electricity. The Advantages over the COIL RELAY, are that tiny amounts of electricity can be used, and electricty can travel at the speed of light, so that a SOLID STATE SWITCH can QUICKLY turn On and Off thousands and millions of times a second -- the COIL RELAY creates a big SPARK every time it turns on and off, and can only move as fast as the steel plate will move- very slow, and eventually the SPARKS destroy the switch! VACUUM TUBES use Electricity, and can switch MUCH faster than the RELAY, however, they have other problems, mostly because they require HUGE amounts of POWER to work, and they require LARGE VOLTAGES to operate. The LOWER the voltage a device uses, the FASTER it can turn on and off the Electricity - Large voltages, and large AMOUNTS of electricity can NOT turn on and off very, very quickly. The HUGE amounts of power mean that large wires have to be used, and the HEAT generated from the HOT, GLOWING "FILAMENTS" or HEATER WIRES, are problems, once you get a large number of TUBES in one location. A single Computer using tubes took as much power as an entire VILLAGE, and since each tube takes up a lot of space, the computer filled many floors on a large building. A typical TUBE computer would be ENIAC, shown below.
Note that there is a huge, powerful fan in the ceiling to get rid of the heat - these were installed every 10 FEET !
The TRANSISTOR works very similar to a VACUUM TUBE. There are typically 3 wires, and a SMALL amount of electricity on MIDDLE WIRE, can ALLOW OR STOP a much LARGER amount of Electricity from flowing across the other two wires. The most common SOLID material used is ordinary GLASS, = SAND = SILICON! The Silicon, or glass, that is used, is very special though, since it is not just melted down from sand like glass windows in your house, but it is very pure glass, and is made into a single CRYSTAL - like Diamonds or Rubies -- where ALL the atoms in the crystal are perfectly arranged in rows and columns- not just mixed up like marbles in a bowl.
CRYSTAL SILICON ( GLASS ) does NOT allow electricity to run through it. To get electricity to flow, the Silicon Glass is mixed with tiny amounts of OTHER ATOMS, and THEN it becomes a 'conductor', allowing electricity to flow through it. Common SOLAR CELLS, used to make electricity from the SUNLIGHT, use ordinary CRYSTAL SILICON, and have chemicals soaked into the top and bottom of the Silicon to make the top and bottom Positive and Negative. The typical Silicon Solar cell has a Bluish color as seen in the example below.
When you add chemicals to pure glass or SILICON, you go from a NON-CONDUCTOR, that does NOT allow electricity, to a SEMI-CONDUCTOR, that allows electricity under certain conditions. I got some pure Silicon Crystal WAFERS or Slices, and heated them up to 2000 degrees Farenheit, and then coated them with ARSENIC and BORON compounds, that, at 2000 degrees, soaked atoms into the Silicon. I did this in Grade 9 in the school Chemistry Lab, but had problems with the 2000 degrees. The wiring I used on the home made fire brick oven was NOT "industrial grade" high temperature wiring, and melted, causing a fire that shut down the school, because of smoke! You could make your own, home- made SEMI-CONDUCTORS, but the chemicals are hazarous, and the high temperatures are difficult to work with, so I would NOT recommend this as a project! But the fact that I ( a kid in school ) could make semi-conductors at all shows how SIMPLE electronics are once you "understand" the principles. By soaking the SILICON with Arsenic and Boron compounds, I made a Semi-Conductor that was Positive on one side, and Negative on the other, and when LIGHT hit the Crystal, it would make electricity -- a Solar Cell. SOLID STATE Transistors are almost identical to this, but there is a THIRD layer in the middle, just like there is a SCREEN in the middle of the Vacuum Tube.
With a TRANSISTOR, we can now use the TINY electricity from the computer Parallel Printer Port or from a BUFFER Chip, to power devices such as LIGHTS and Motors, which use BIG amounts of power. A Transistor can also switch OFF or ON power in the REVERSE, so that if you need a signal to be OFF when the Printer Port is putting out an ON, you can wire in a transistor to CHANGE or REVERSE the signal. If you want to power 8 LED lights on a single wire, you can wire in a transistor to take the tiny power from a DIGITAL Signal, and put out a POWER signal that has enough power to run 8 LEDs easily. You can wire in a transistor to take the ON / OFF signal from a BUFFER CHIP, and turn ON and OFF a big RELAY, and the contacts on the relay can then turn ON and OFF much BIGGER devices such as Motors and LightBulbs. Transistors are very handy in this type of project.
WHERE ARE TRANSISTORS USED?
Just about every device that uses electricity will have transistors in it. A Cell Phone, a Radio, a Computer, Microwave Ovens, Kitchen Appliances, even Toasters now have transistors in them.
The transistor above, uses 6 VOLTS to turn on and off 1,500 VOLTS to the HORIZONTAL circuits on the TV! That is a LOT of work for one little Transistor. The transistor is BOLTED to a HEAT SINK, a piece of metal with fins on it to remove the heat. This TV was over- heated, and the heat sink was too small to take away the heat, so the transistor failed. When I fixed it, I put in a bigger heat sink. Shown in a red square, is a 7 PIN Voltage Regulator Chip with another little heatsink. When the 1500 Volt transistor shorted, it sent 1500 volts into the 6 volt pin on the Regulator, blowing it up as
well, and this had to be replaced.
When a computer POWER SUPPLY clogs up with dust and dirt, the aluminum heat sinks no longer take away heat from the transistors, and they start to fail. Usually on a power supply like this, the OUTPUT transistors fail, and OUTPUT CAPACITORS overheat and dry out and BOIL, cracking their aluminum can covers. The high voltage, 300 to 400 volt INPUT capacitors and transistors rarely ever fail.
The Portable Home Phone ABOVE was thrown out in the rain, in the recycling. I knew immediately what was wrong with it- just like TV , VCR, DVD, STEREO, and most Remote Controls, the rubber buttons on the keypad absorb oil and moisture, which gets on the green circuit board under the keys, and shorts out the buttons. Once I cleaned the buttons, the unit worked perfectly. Most people do not know that you can take apart the Remote Control or Device with the keypad, and wash the rubber keypad and the green circuitboard, in the sink with hot water and soap, and once thoroughly dried with a hair dryer, the unit is like new. This phone has a multilayer green board though, so it is easier to clean the key area with a damp cloth, so that it dries easily-- the rubber keys were washed in the sink with hot water. The Portable phone has Transistors in BLUE, and LED lights in RED, as well as switches, capacitors, diodes, transformers, etc. all of which can be used for a ROBOT Project, and are FREE...
The Computer MOTHERBOARD, above, had the HEATSINK on the Computer "CPU" (INTEL PENTIUM) clog solid with dust and dirt, so that it overheated, using too much power. The heat and the huge amount of power, heated up the CAPACITORS ( shown in BLUE ) until they boiled the "electrolyte" insulating fluid inside the aluminum cans, splitting the tops open, and foaming liquid out the tops. You can see the dust on the sides of capacitors, blown out from where the CPU and heatsink would be located, on the black plastic frame. This also over- stressed the power supply, and boiled capacitors on it as well. In many cases, the motherboard could be repaired by just replacing the cracked capacitors, but almost no one bothers to do the repairs- it costs more in Technician TIME to replace the parts, than the cost of a new motherboard. The power TRANSISTORS are seen all around the CPU, as shown in ORANGE.
The DVD PLAYER, above, was thrown out in the rain in a pile of garbage. There is nothing wrong with it at all, except that it is NOT a BLUE RAY player, and like tens of millions of DVD players around the world, it is just thrown out. It has a great little 110 Volt to +5 Volt power supply, and lots of resistors, capacitors, diodes, and transistors, as well as motors and mechanical parts. I could use this just for ROBOT Parts, or, take out all the circuits that I don't need, and use it as a BASE to put a circuit board on top of for an INTERFACE. That way, it already has a 110 Volt power supply for the +5 Volt interface, and it has lots of spare diodes, LED lights, capacitors, resistors, motors, gears, etc. to build the interface and a ROBOT with! This DVD player is PERFECT for kids to use for PARTS for homemade robots and interfaces, and its FREE.
Just like the DVD player thrown out in the rain in the garbage, this VHS Video Cassette Recorder ( VCR) was thrown out. Again, there is nothing wrong with it except that it is NOT a Blue Ray Player, so it is thrown out, like millions of others around the world. It has Transistors, Diodes, Resistors, Capacitors, Motors, Gears, LED lights, and a wonderful 110 Volt power supply that includes +5 volts, and +9 Volts to run the motors. ALL FREE !
The DVD Automotive, 7 inch TV Player, above, has dozens of transistors, large and small. This unit was thrown out since the DVD DISC laser reader no longer worked, but the TV Flat Panel is fine, and has Input jacks for games and other VCR's, DVD's and Cable, etc.
Above is a Dollar Store FM radio, showing the FM Digital Chip, and on the back of the circuitboard are two large transistors identical to the ones I use on the computer interface. This ONE dollar radio has a volume control, FM chip, transistors, diodes, capacitors, LED light, earphones, plug in jack, packaging, plastic case parts and buttons, etc. that would cost me $45 to buy separately in Canada.!!
TRANSISTORS USED IN THIS PROJECT
The picture above, has the most common SIZES of transistors. For our project, we will probably only use the SECOND SMALLEST. The smallest "SMT" or Surface Mount Technology, is perfectly good, but just too small for most people to handle very well. I use these often, but I have been using soldering tools for a long time, and have found ways to use them easily. The common type shown with the orange arrow is inexpensive, reliable, and easy to work with.
THERE ARE TWO KINDS OF TRANSISTORS that we will work with, and they appear identical, but have REVERSE NEGATIVE and POSITIVE atoms in the SILICON. One turns on electricity when you make the CENTER lead POSITIVE, the other kind turns on electricity when you make the CENTER LEAD NEGATIVE.
APPROPRIATELY, these two types are called NPN and PNP. The N is for NEGATIVE, and the P is for POSITIVE. This refers to the ATOMS used to make the Silicon CONDUCTIVE, the same way I used ARSENIC and BORON compound's Atoms to make my Silicon disks Positive and Negative to Conduct electricity when hit by light particles (PHOTONS). The NPN is used more often since it conducts electricity better. Most sizes of transistor have what is know as a COMPLIMENTARY PAIR - almost identical transistors with the exact OPPOSITE electrical values. This is very handy for projects, since a COMPUTER OUTPUT can be made to either turn ON electricity with a "ONE" or + 5 VOLTS, using an N P N, or the COMPUTER OUTPUT with + 5 VOLTS can turn OFF electricity by using a P N P. ( Note that +5 Volts is NOT Negative, so the transistor turns OFF ! PNP only turns on when it gets a NEGATIVE signal on the Center or Control input.) In my robot projects, I only use transistors to turn either ON or OFF, just like the COMPUTER either puts out a +5 " ON " or a Zero Volt " OFF". This is just using the transistors as DIGITAL SWITCHES. +5 Volts and ZERO Volts = ON and OFF = Digital Values 1 and 0.
As I have pointed out earlier, there are thousands of different LED lights, thousands of different RELAYS, thousands of different PARALLEL port wirings, and there are thousands of different TRANSISTORS. However... I have found by experiment, that you can use electronic parts with HUGE DIFFERENCES and still "get away with" all the many different parts. For Example, Radio Shack in Canada was dropping all the electronic parts, one by one, over 6 months to a year, just as I was designing my first simple, cheap, interface, so every time I went back to whatever store was near me, I had fewer and fewer parts to choose from (They did NOT "publicly" state that they were changing their product line)... Even with horrible, incorrect transistors, and diodes and resistors, I could still build electrical circuits that actually WORKED. This is because the parts I was using were much stronger and better than the job I was using them for- example - the 2N2222 Transistor can easily handle 40 VOLTS, but I was just using it to control small amounts of +5 Volts, so that even with the wrong resistors, the transistor still worked just fine. When I look on the WEB for parallel Port interfaces, I can find hundreds of different designs, using hundreds of different chips and transistors and parts. Some diagrams use the same CHIPS, but have different resistors and diodes, etc. so again, there can be fairly big differences in the VALUES of parts, and they still work. An engineer can sit down with a SINGLE, SPECIFIC, Transistor, in a SPECIFIC circuit, and calculate EXACTLY the correct value of the Resistors and Diodes and Capacitors etc. to use. This is RARELY ever done, since there are "COMMON " values of resistors that are available on the store shelves, around the world, so that getting an EXACT Resistor would mean making a SPECIAL ORDER from the FACTORY, and waiting until they manufactured it and shipped it to you! When I look at electronic circuit boards, I can almost instantly tell 1970's Hewlett Packard electronics, because every single Resistor is a special, High Quality, Custom Ordered, Extra Precision, Flameproof (blue) resistor. HP Scientific Equipment gained a reputation in Hospitals and Laboratories around the world for having Incredible accuracy and Quality. Most common household Electronics like TV's, Radio's, Microwaves, CD and DVD Players, etc. will all have "Standard" value, common resistors (brown), that you can find easily, in any electronic store. These VALUES of the resistors are NOT CORRECT- they are just "CLOSE" enough to work "OK".
SO, ... none of the values of any of the parts that I am using are absolutely "correct" -- they are just "close enough" to work. If you CANNOT FIND the EXACT same parts and values, you can often substitute or replace the part with something "CLOSE", and it will still work! (NOTE THAT THERE ARE A FEW GUIDELINES IN WHAT TO SUBSTITUTE- I will go over these later) I have deliberately used horrible Transistors, Resistors, Diodes, etc. and the circuits still worked "OK" -- However, if the values are TOO far out, the transistors can slowly be destroyed over time, and eventually the circuit will fail ( I have had that happen over a year or two ).
The transistors I use are COMPLIMENTARY PAIRS, or very "close" values for this type of project. The first set is the popular 2N2222 NPN which has limiting voltages of about 6 volts for the CONTROL wire and 40 volts for the OUTPUT. Its COMPLIMENT is commonly the 2N2907 PNP, which has limits of 5 volts for the CONTROL wire, and 80 Volts on the OUTPUT. Since I am using only TINY amounts of 5 Volts IN and 5 volts OUT, both are much more powerful than needed. The second set of Transistors is a COMPLIMENTARY PAIR of the 2N3904 NPN (6 volt control and 40 Volt output) and the 2N3906 PNP ( 5 volt CONTROL and 40 volt output). There are THOUSANDS of other similar transistors that all will work! I am trying to choose the least expensive and the easiest to find. Unfortunately, over the years, there are different NUMBERS on the SAME electronic parts, so you may have to look for the "NEW" numbers that are most often used -The 2N2222 and 2N2907 are often called NTE123 and NTE159, and the 2N3904 and 2N3906 are, interestingly, the SAME NUMBERS, NTE 123 and NTE 159, which shows how "different" parts can do the same job if they are "CLOSE".
