Every time we say “We’ve seen it all”, along comes a project that knocks us off. 60 year old [Mark Nesselhaus] likes to learn new things and he’s never worked with hardware at the gate level. So he’s building himself a 4-bit Computer, using only Diode-Transistor Logic. He’s assembling the whole thing on “card board” perf-board, with brass tacks for pads. Why — because he’s a thrifty guy who wants to use what he has lying around. Obviously, he’s got an endless supply of cardboard, tacks and Patience. The story sounds familiar. It started out as a simple 4-bit full adder project and then things got out of hand. You know he’s old school when he calls his multimeter an “analog VOM”!
It’s still work in progress, but he’s made a lot of it in the past year. [Mark] started off by emulating the 4-bit full adder featured on Simon Inns’ Waiting for Friday blog. This is the ALU around which the rest of his project is built. With the ALU done, he decided to keep going and next built a 4-to-16 line decoder — check out the thumbnail image to see the rats nest of jumbled wires. Next on his list were several flip flops — R-S, J-K and D types, which would be useful as program counters. This is when he bumped into problems with signal levels, timing and triggering. He decided to allow himself the luxury of adding one IC to his build — a 555 based clock generator. But he still needed some pulse shaping circuitry to make it work consistently.
[Mark] also built a finite-state-machine sequencer based on the work done by Rory Mangles TinyTim project. He finished building some multiplexers and demultiplexers, and it appears he may be using a whole bank of 14 wall switches for address, input and control functions. For the output display, he assembled a panel using LED’s recovered from a $1 Christmas light string. Something seems amiss with his LED driver, though — 2mA with LED on and >2.5mA with LED off. The LED appears to be connected across the collector and emitter of the PNP transistor. Chime in with your comments.
This build seems to be shaping along the lines of the Megaprocessor that we’ve swooned over a couple of times in the past. Keep at it, [Mark]!
When the story of an invention is repeated as Received Opinion for the younger generation it is so often presented as a single one-off event, with a named inventor. Before the event there was no invention, then as if by magic it was there. That apple falling on Isaac Newton’s head, or Archimedes overflowing his bath, you’ve heard the stories. The inventor’s name will sometimes differ depending on which country you are in when you hear the story, which provides an insight into the flaws in the simple invention tales. The truth is in so many cases an invention does not have a single Eureka moment, instead the named inventor builds on the work of so many others who have gone before and is the lucky engineer or scientist whose ideas result in the magic breakthrough before anyone else’s.
The history of computing is no exception, with many steps along the path that has given us the devices we rely on for so much today. Blaise Pascal’s 17th century French mechanical calculator, Charles Babbage and Ada, Countess Lovelace’s work in 19th century Britain, Herman Hollerith’s American tabulators at the end of that century, or Konrad Zuse’s work in prewar Germany represent just a few of them.
So if we are to search for an inventor in this field we have to be a little more specific than “Who invented the first computer?”, because there are so many candidates. If we restrict the question to “Who invented the first programmable electronic digital computer?” we have a much simpler answer, because we have ample evidence of the machine in question. The Received Opinion answer is therefore “The first programmable electronic digital computer was Colossus, invented at Bletchley Park in World War Two by Alan Turing to break the Nazi Enigma codes, and it was kept secret until the 1970s”.
It’s such a temptingly perfect soundbite laden with pluck and derring-do that could so easily be taken from a 1950s Eagle comic, isn’t it. Unfortunately it contains such significant untruths as to be rendered useless. Colossus is the computer you are looking for, it was developed in World War Two and kept secret for many years afterwards, but the rest of the Received Opinion answer is false. It wasn’t invented at Bletchley, its job was not the Enigma work, and most surprisingly Alan Turing’s direct involvement was only peripheral. The real story is much more interesting.
A team based in Russia has developed a program that has passed the iconic Turing Test. The test was carried out at the Royal Society in London, and was able to convince 33 percent of the judges that it was a 13-year-old Ukrainian boy named Eugene Goostman.
The Turing Test was developed by [Alan Turing] in 1950 as an existence proof for intelligence: if a computer can fool a human operator into thinking it’s human, then by definition the computer must be intelligent. It should be noted that [Turing] did not address what intelligence was, but only tried to identify human like behavior in a machine.
Thirty years later, a philosopher by the name of [John Searle] pointed out that even a machine that could pass the Turing Test would still not be intelligent. He did this through a fascinating thought experiment called “The Chinese Room“.
For several years, [Jim] has wanted to construct a fully-mechanical universal Turing machine. Without the help of any electronic circuits or electrical input, his goal was to build the machine using simple hand tools and scrap materials.
If you are not familiar with the concept of a Turing machine, they are devices that manipulate symbols or input from a strip of tape, according to a set table of rules. By definition, a Turing machine should be adaptable to simulate the logic of any computer algorithm, albeit in a much slower fashion than you would see from a computer.
He has replaced the strip of tape with a wire grid, and the symbols have been implemented in the form of ball bearings placed on the aforementioned grid. His hand-cranked machine uses magnets to lift the input symbols from the grid, processing them according to the rules table he routed out of a wood block.
The implementation is definitely clever, though [Jim] admits it is not without its problems. He took it to Maker Faire UK, and most people didn’t quite understand what they were seeing without a full explanation. The machine is not quite as reliable as he would like it to be, and he would like to make it a bit more powerful as it currently would take months to add two numbers together.
Keep reading to see a brief video demo of his Turing machine in action, and check out his blog if you want to see more information on how the machine was built.
Interested in seeing more Turing machines? Check out these two machines we featured a while back.
This interesting use of Lego popped up on the mailing list of the University of Bergen. Build by a group of Norwegian Danish students, it’s a simple computer that implements Alan Turing’s design from 1937. Having both read and write functions, it implements its own (somewhat inefficient) medium of non-volatile memory. What we find interesting is that rather than move the ‘tape’ through the machine, the machine rolls over the tape. Thanks to [Thorsten] for the tip.