Self-made transistor RAM

[AlekseiX86]

I a'm newbie in circuit , but i have an idea to create simplest computer using only discrete diods and transistors.

I want to ask about reliability of such computer , especialy about reliability of simplest RAM memory made from discrete elements. I mean would no it be often fail some parts of computer?
And how many transistors will be include such memory , for examle 100 Bytes.
Thanks for helping.

 

[NuLED]

I am a newbie too but I think if you are wondering if this type of device will fail less easily than a "regular" computer, I think it might be about the same. The semiconductors inside diodes and transistors are just as sensitive to damage.

A more robust (tougher) circuit might be one that only uses electromagnetic RELAYS (like before the days of semiconductors) but you will need many hundreds of of them if you want to construct all the logic gates to create a basic calculator, using a memory space.

I could be wrong but this is my understanding so far of electronics.

 

[Twodio]

I already saw some creations and computers using simple BC548 transistor some resistors and leds to build a basic 2-bit or 4-bit computer, but even i was give up because i dont had some materials including resistors.

A simple 4-bit processor use more than 15 transistor, because they are used to build AND, OR, NOT, XOR, etc gates.

here go some of pages that i've found and saved as study material:

http://www.metafysica.nl/circuit.html
http://www.waitingforfriday.com/index.php/4-Bit_Computer

Good lucky for you ...

 

[duke37]

Chips are very reliable, it is the connections between them which are the problem.

100 bytes = 800 bits

I think you will need two transistors for each bit = 1600 transistors plus maybe the same number of resistors.

Relays are not very reliable as was found when decrypting the Enigma code. This led to the development of the computer based on valves (tubes).

 

[Raven Luni]

There was a great article I came across ages ago (cant remember where) that talked about this stuff from the ground up from the bistable multivibrator (2 transistors) to latches, flipflops etc. with some good points about clocking and edge triggered inputs

 

[(*steve*)]

If you want reliable, you probably want to look at magnetic core memory.

Sure, transistors aren't really part of it, but there are people making this just for the fun of it!

 

[AlekseiX86]

If you want reliable, you probably want to look at magnetic core memory.

Sure, transistors aren't really part of it, but there are people making this just for the fun of it!

Thanks , it is really good idea to do magnetic memory.
But i have several questions about making such memory by yourself :
Is it hard to make? And what parts I would need for it?

 

[gorgon]

Just from the top of my memory, a static RAM bit cell needs about 5 or 6 transistors, that's 4000 - 4800 transistors for 100byte. In addition to that you'll need several 10s of transistor to decode the address and select each byte. In addition to the transistors you'll need a load of resistors, and maybe some diodes.

 

[BobK]

Just from the top of my memory, a static RAM bit cell needs about 5 or 6 transistors, that's 4000 - 4800 transistors for 100byte. In addition to that you'll need several 10s of transistor to decode the address and select each byte. In addition to the transistors you'll need a load of resistors, and maybe some diodes.

Actually you can build a static RAM cell with only 2 transistors. It is simply a discrete SR flip flop.

Bob

 

[Twodio]

Actually you can build a static RAM cell with only 2 transistors. It is simply a discrete SR flip flop.

Bob

Can you explain me how? you look know it very well.

 

[BobK]

It is just a bistable multivibrator.

http://www.electronics-tutorials.ws/waveforms/bistable.html

Bob

 

[NuLED]

Surprisingly, I am able to help with this question for a change!

I have been studying basic gates also lately. Anyway I think this is what Bob is talking about (the set/reset basic flip flop). I found a good YouTube video for you that shows it in operation:

And here is the schematic:

http://www.pcbheaven.com/wikipages/images/transistorcircuits_1235488532.jpg

See here also:

http://www.pcbheaven.com/wikipages/Transistor_Circuits/

 

[AlekseiX86]

Intresting : is it possible to made computer which will be able to render 3D graphic and high optimize for this. Ofcourse using only chips. In video ram chip will be colors of all pixels , and then just need to made controller which will be convert video signal in RCA (like in SEGA consoles).
For example 640x480 = 307 200 pixels.
Or in another case just 2D graphic.
But i think it will be necessary high speed ram chips and the same chip logical elements.
And it is not hard to write transaltor from some selfmade high language to this computer's binary code.
No OS , just render for render code processing.
How do you think about this?
Thanks for reading.

 

[BobK]

Yes, Intel, NVIDIA and AMD, do this quite well.

Bob