Bil Herd: Computing with Analog

When I was young the first “computer” I ever owned was an analog computer built from a kit. It had a sloped plastic case which had three knobs with large numerical scales around them and a small center-null meter. To operate it I would dial in two numbers as indicated by the scales and then adjust the “answer” by rotating the third dial until the little meter centered. Underneath there was a small handful of components wired on a terminal strip including two or three transistors.

Science Fair Analog Computer

Science Fair Analog Computer

In thinking back about that relic from the early 1970’s there was a moment when I assumed they may have been using the transistors as logarithmic amplifiers meaning that it was able to multiply electronically. After a few minutes of thought I came to the conclusion that it was probably much simpler and was most likely a Wheatstone Bridge. That doesn’t mean it couldn’t multiply, it was probably the printed scales that were logarithmic, much like a slide rule.

Analog slide rule on digital calculator

Old meets new: Analog and digital computation

Did someone just ask what a slide rule was? Let me explain further for anyone under 50. If you watch the video footage or movies about the Apollo Space Program you won’t see any anyone carrying a hand calculator, they didn’t exist yet. Yet the navigation guys in the first row of Mission Control known aptly as “the trench”, could quickly calculate a position or vector to within a couple of decimal places, and they did it using sliding piece of bamboo or aluminum with numbers printed on them.

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The Entire Commodore 64 Library In Your Pocket


[sweetlilmre] is just beginning his adventures in retrocomputing, and after realizing there were places besides eBay to buy old computers, quickly snagged a few of the Amigas he lusted after in his youth. One of the machines that didn’t make it into his collection until recently was a Commodore 64 with Datasette and 1541 drive. With no tapes and a 1541 disk drive that required significant restoration, he looked at other devices to load programs onto his C64.

These devices, clever cartridge implementations of SD cards and Flash memory, cost more than anyone should spend on a C64. Realizing there’s still a cassette port on the C64, [sweetlilmre] created Tapuino, the $20 Commodore tape emulator

The hardware used to load games through the Datasette connector included an Arduino Nano, a microSD breakout board, a 16×2 LCD, some resistors, buttons, and a little bit of wire. The firmware part of the build – available here on the Git – reads the .TAP files off the SD card and loads them into the C64.

[sweetlilmre] posted a very complete build post of the entire device constructed on a piece of protoboard, Pop that thing in a 3D printed case, and he can have the entire C64 library in his pocket.

Cold War Clock is all Tubes

A clock built from tubes


Clocks are great projects to build. They serve a real purpose, and there’s a wide variety of ways to implement a unique timepiece. [Hank]‘s Cold War Clock only uses parts and technologies that were available in 1959. It contains no semiconductors, but has an audible alarm and reasonable time accuracy.

Looking through the hand drafted schematics, you’ll find a number of Dekatron tubes. These vintage components are used as registers to store and count the time. [Hank] found some cheap Soviet Dekatrons, but had to machine his own sockets to connect them. These tubes do the counting, but the actual display consists of nixies.

A cost estimate puts this clock at $2130 in 1959, which equates to $17040 today. Clearly this would be outside the price range of most hobbyists. The actual build cost [Hank] around $1600.

There’s some intricate details in this build. The front panel has an authentic look to it, and the manual has instructions for “demolition of clock to prevent enemy use.” [Hank] calls it a “creative anachronism.” In a sense, it’s a reproduction of a product that never actually existed.

A video of this clock in action, including the Cold War era alarm, is after the break.

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Reverse Engineering Unobtanium


If you listen to [Bil Herd] and the rest of the Commodore crew, you’ll quickly realize the folks behind Commodore were about 20 years ahead of their time, with their own chip foundries and vertical integration that would make the modern-day Apple jealous. One of the cool chips that came out of the MOS foundry was the 6500/1 – used in the keyboard controller of the Amiga and the 1520 printer/plotter. Basically a microcontroller with a 6502 core, the 6500/1 has seen a lot of talk when it comes to dumping the contents of the ROM, and thus all the code on the Amiga’s keyboard controller and the font for the 1520 plotter – there were ideas on how to get the contents of the ROM, but no one tried building a circuit.

[Jim Brain] looked over the discussions and recently gave it a try. He was completely successful, dumping the ROM of a 6500/1, and allowing for the preservation and analysis of the 1520 plotter, analysis of other devices controlled by a 6500/1, and the possibility of the creation of a drop-in replacement for the unobtanium 6500/1.

The datasheet for the 6500/1 has a few lines describing the test mode, where applying +10 VDC to the /RES line forces the machine to make memory fetches from the external pins. The only problem was, no body knew how to make this work. Ideas were thrown around, but it wasn’t until [Jim Brain] pulled an ATMega32 off the top of his parts bin did anyone create a working circuit.

The code for the AVR puts the 6500/1 into it’s test mode, loads a single memory location from ROM, stores the data in PORTA, where the AVR reads it and prints it out over a serial connection to a computer. Repeat for every location in the 6500/1 ROM, and you have a firmware dump. This is probably the first time this code has been seen in 20 years.

Now the race is on to create a drop-in replacement of what is basically a 6502-based microcontroller. That probably won’t be used for much outside of the classic and retro scene, but at least it would be a fun device to play around with.

Printing Text with a Chart Recorder

A chart recorder printing 'Hello World'

Chart recorders are vintage devices that were used to plot analog values on paper. They’re similar to old seismometers which plot seismic waves from earthquakes. The device has a heated pen which moves across a piece of thermally sensitive paper. This paper is fed through the machine at a specified rate, which gives two dimensions of plotting.

[Marv] ended up getting a couple of discontinued chart recorders and figured out the interface. Five parallel signals control the feed rate of the paper, and an analog voltage controls the pen location. The next logical step was to hook up an Arduino to control the plotter.

However, once the device could plot analog values, [Marv] quickly looked for a new challenge. He wanted to write characters and bitmaps using the device, but this would require non-continuous lines. By adding a solenoid to lift the pen, he built a chart recorder printer.

After the break, check out a video of the chart recorder doing something it was never intended to do. If you happen to have one of these chart recorders, [Marv] included all of the code in his writeup to help you build your own.

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Marvin’s Marvelous Mechanical Museum

Don’t call it an arcade. There are arcade-like things about it… like dance-based video games, Skee-ball, and tickets — oh so many tickets. But Marvin’s Marvelous Mechanical Museum is a one-of-a-kind that you need to visit next time you’re in the North suburbs of Detroit, Michigan.

[Marvin] was there in person, as he is many days. He talked with us for a few minutes and we’ve folded his interview, along with footage of many of the attractions, into the video above.

He’s been collecting for more than three decades. The attractions are packed into every bit of floor space, spilling up onto the walls, and hanging from every spot in the ceiling. There are true antiques from both home and abroad that could be referred to as automatons, rows of fortune tellers, a track of large airplane models that make a loop around the establishment when fed a quarter, and much more.

Some of the attractions were build for him, like the robot band you can make out behind [Marvin] during the interview. It is a MIDI-based build that allows songs to be selected from a touchscreen. Soon to be on exhibit is a Tesla-coil-based offering which [Marvin] commissioned after taking second place to [Nicolai Tesla] on a list of oddest museums.

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A Fully Mechanical 3D Printer is Mind Blowing

mechanical 3d printer

It’s been a while since we’ve been seriously impressed with a project like this one. [Daniël de Bruin], a student at the Art Academy in Utrecht has just put the final touches on his mechanical 3D printer.

That’s right. Mechanical.

No computers, no motors, just the power of gravity. It could have been built 100 years ago.

The machine uses a 15kg weight to power the mechanism — it does need to be reset during the print, but that’s a small price to pay for this kind of mechanical automation.

He uses a type of clay in a paste extruder that slowly deposits the material on the build platform. To program the machine, there is a small guiding mechanism that follows the contour of a bent aluminum wire. This allows you to make any number of symmetrical and circular objects.

[Daniël] says he was inspired to build this machine because he loves 3D printing — but at the same time, he feels like it’s kind of like cheating. Beyond pressing the print button, there’s no real human interaction.

I love technology but how can I reclaim ownership of my work? Perhaps by building the machine that produces the work. Perhaps by physically powering the machine, which I built, that produces the work. in hopes of rediscovering the sense of having created something, I create.

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