Diodes as transistors

Is it possible to use two transistors back to back "leg PN leg leg NP leg" to make a transistor? I can't do too much reasearch right now because I'm on a cruise ship and the internet is expensive. I had the idea a few days ago and its killing me.

I started with the idea of building a TTL computer. Once I complete that I wanted to design the same computer out of transistors. I'm thinking about skipping transistors and going with diodes!

Another question is can LEDs be used? How would you determine the speed that the hacked together transistor could operate at? I would love to have a computer built out of LED silicon. :)

Would there be any benefit with using diodes over transistors? I want to build the computer with the earliest technology available while ignoring relays and tubes.

Love to hear your ideas!

Thanks, Grant

"Grant Stockly"

....... Phil

Assuming you meant "two diodes"...

I've tried this, long ago. It doesn't work. Only later did I understand the mechanisms of transistor physics enough to know why. Well, I sort of understand it ;-)

I've tried making an SCR out of two transistors, too. That didn't work either.

In a nutshell, the base works because it's *thin*. When you have two diodes, you don't have a thin base. The physical geometry of the transistor's internals is important to the way it operates.

Two diodes will not function as a transistor. I tried it in the 1950's. You can study the transistor theory to understand why. There is no technology between vacuum tubes and transistors that will effectively make a computer. There are some magnetic and pneumatic amplifiers that can have some basic logic functions but they are much larger, expensive, and complicated than transistors.

Keep learning and trying new things.

Don Young

With a diode added to the two transistors you can get an SCR effect. Some positive feedback, via C1, may help.

Nope. The Pride of America. Its about 950 feet long, 200 feet wide,

Thanks for all the responses. Too bad it won't work. : ( I will still plan on building a transistor based computer. I think I want to model the 8080 so that I can run CPM on it. Don't worry, I plan to put a few thousand LEDs in the data paths to show the computer working. :)

Grant

good luck - I think that is pretty ambitious for descrete trannies.

not thought of doing the 4004 - bearing in mind it's historical importance as the first CPU IC? Your creation would then have a symbolic application with a little 4004 mounted next to it or sunnik (still got one in a carrier some where)

Whatever you do, wire-wrap the legd of the trannies and solder then after - a rats nest will suffer far less from parasitic oscilation that will muck it all up - depending on how fast you want to clock it of course.

Actually, diode logic was popular in early computers (or at least early solid-state computers). A logic gate typically used one diode for each input, all tied to the base of a switching transistor. The purpose of the diodes was to isolate the inputs from each other. If any one of the diodes conducted, the transistor turned on. Depending on how you defined your logic states, this could be a NOR or NAND.

Diodes were also used in matrices for decoding more advanced functions.

I have in my collection some early "mainframe" modules made from two tiny circuit boards stacked vertically about an inch apart, with vertically-aligned diodes soldered between the top and bottom board, and the transistor similarly sky-wired. The boards are held in a plastic inverted U carrier and the bottom board has pins that allowed it to be plugged into the backplane. When a module failed, you could just yank it out and replace it.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Hi, Grant. Life is short. You might not know it, but you can make a computer with only NAND gates, which you can make out of several discrete transistors. You'll need an awful lot of NAND gates, of course.

about this: make a few logic gates with discrete transistors, try a couple of latches, and then move on to learn other things. You could literally do the study to complete one or two college-level electronics courses in the time it would take to complete your '60s-era "computer".

To become proficient in electronics, there's a lot more to learn. Sample some of the other things, too.

Good luck Chris

Something like this will work as a SCR using two transistors. It's called a SCS for (silicon controlled switch).

V+ + | LOAD | E \\| PNP |B------------+ /| C R C |/ +---\\/\\/\\-----+------------B| NPN Trigger |\\ E | | V-