Duo Basic: An All-Logic Chip Educational Computer

DUO

Way back before the days of microcomputers, a few very lucky students first got their hands wet with microcomputer trainers. These simple devices used common logic chips, lights, and switches to perform calculations; basically, a very small and simple computer. [Jack] has just released his DUO Basic 8-bit educational computer, a computer designed entirely around logic chips just as was done in the olden days.

The entire computer except for a single EEPROM giving the computer 256 bytes of ROM, three registers, and two instructions (condition jmp and add). This allows for simple programs to be written just by flipping switches and hitting buttons – it doesn’t get much more ‘bare metal’ than that.

[Jack] has an online assembler and emulator for the DUO Basic along with a few example assembly programs. Of course, all the schematics and block diagrams are available on his site, along with a nice introductory video, shown below.

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An Overly-Complicated Logic Chip Clock

Clock

When a normal alarm clock just won’t do, the only option is to build your own, entirely out of discrete logic chips. [jvok] built this alarm clock for last year’s 7400 Logic Competition. In a desire to go against the grain a little bit, [jvok] decided to use 4000-series logic chips. It was allowed under the rules, and the result is a wonderful example of what can be done without a microcontroller.

Most clock projects we’ve seen use a single button to increase each digit. [jvok] wanted to do something unique, so he is able to set his clock with a ‘mode’ button that allows him to independently set the hours, minutes, and seconds. He’s only ever seen this method of setting a clock’s time used with microcontroller-based projects, and translating even that simple code into pure circuitry is quite impressive.

This clock also includes an alarm function, set by a bunch of DIP switches in binary coded decimal. It’s a great piece of work, and deserving of much more attention than it received during the Open Logic Competition.

A Twitter Connected Mechanical Calculator

The TwitALU

Two students at the University of Bristol wanted to create a computer to demonstrate how ALUs work. The result is the TwitALU, a Twitter connected mechanical calculator.

The device uses a custom 7400 series ALU based on the famous MOS 6502 processor. Instead of doing the calculations on a silicon die, the ALU drives mechanical relays. This produces a nice clicky-clacky sound as the calculation is computed.

To start a calculation, you tweet @twittithmetic with your input. A Raspberry Pi is used to load the instructions into the ALU. Once the computation is done, it’s tweeted back to you and displayed on the Nixie tube display. It’s not efficient, or fast, but it does the job of demonstrating the inner workings of the device while doing simple math.

The device’s schematics are all available on the website, and are helpful for understanding how a simple ALU works. After the break, check out a quick clip of the TwitALU in action.

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The Nibbler: a 4-bit CPU built with 7400 logic

nibbler-schematic

Maybe we shouldn’t say “built” since [Steve Chamberlin] hasn’t actually heated up his iron yet. From the finished schematic above that is puzzling at first, until you realize the scope of the project. His Nibbler implements a 4-bit CPU using 7400 logic chips. Because he’s come up with the architecture himself he’s taking a lot of steps to check all of his work before committing to a PCB.

We linked to his category for the project which is still in progress. Most recently he wrote a program to prove that it’ll run on the hardware. That’s a feat considering this is still just a design idea. It was made possible because he wrote a simulator based on the design. The C++ tool simulates data and control buses and features a full set of debugging tools.

Careful testing of the design before the build is the best possible way to go. The simulator and debugging tools will be useful for software development even after the hardware is built. And testing before wiring is a must as these things get out of control quickly in terms of soldering complexity.

[via Dangerous Prototypes]

Hackaday Links: Sunday, May 12th, 2013

hackaday-links-chain

[Johnathan Crawford] isn’t bashful about tearing the insides of his truck apart. He’s built his own remote starter using a Raspberry Pi.

We vaguely remember hearing about a startup that planned to deliver tacos using quadcopters instead of people. We assume that company was a bust but here’s the concept in action at the 2013 RoboGames [thanks Don].

On the topic of food: pizza and joysticks… do they go together? Perhaps. Here’s a joystick made out of an empty pizza box (note the remains of grease stains inside).

[Jonathan] brings to our attention the problem of running out of fingers to press all the buttons on your Monome at just the right moment. No worries, just add some solenoids to act as extra fingers.

Apparently some Samsung cameras (NX20, NX210 and NX1000) can use their USB port as a shutter release. The trick is finding the right resistor values for the ID pin [thanks Janne].

Plagued with a tablet dock that wasn’t weighty enough to prevent the device from tipping over [John] filled base with lead to keep the thing upright.

[Helmut's] bathroom had no windows. He faked one using an Arduino and an RGB led.

And finally, as a reward for all the readers that made it to the bottom of the article, here’s a gem of a project. [Charlie] was inspired by the recent logic combo lock post to send in his own plans for a lock he made years ago. Unfortunately he can’t find the pictures from the build but the theory behind it is quite engaging.

7400 Logic Competition winners announced

The 7400 Logic Competition has drawn to a close. The winners were announced and there are quite a few of them. There were fifteen first place winners named, nine second place, and nineteen third place projects. The bounty of quality entries is a testament to the popularity of the contest. It helps to have a wide range of prizes and the post linked above lists all of the sponsors who donated goodies as an incentive.

The board seen above was awarded the reader’s choice, to which the grand prize was awarded. It is a 7400 series calculator. [Umair Mukati] and [Naveed Ahmed] — both are students at the Institute of Industrial Electronics Engineering in Karachi, Pakistan — developed the device as part of a class project. It is capable of adding or subtracting two digit numbers. This includes support for negative numbers as results. We’ve embedded a video demo of the calculator in action after the break.

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7400 frequency counter

This frequency counter is [Miguel Pedroso's] entry in the 7400 Logic contest. After looking at the design we think this is a perfect project for those who have not worked with logic ICs before. The concept is simple and [Miguel] does a great job of explaining his implementation.

At its heart the device simply counts the oscillations of an input signal for one second, then latches the total to the 7-segment displays before zeroing the counter block and starting over. Six 4029 decade counters give the device a range of 1MHz. A set of 4511 BCD to 7-segment decoders translate the count to the display. A 4521 frequency divider chip uses an on-board 4.194304 MHz crystal oscillator to time both the display latching and the counter clearing. [Miguel] mentions that tuning the load capacitors is a bit tricky. Since breadboards have their own capacitance issues it may be necessary to change the load capacitor values when moved to protoboard or the crystal won’t start oscillating. You can see those caps are not the same value, but the tests in the video after the break show that this is pretty much spot-on.

If you’d rather give this a try in HDL here’s an FPGA-based frequency counter from which you can draw some inspiration.

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