Drawing With Legos

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There are a number of elaborate Lego creations out there, but you probably haven’t seen something quite like [Andrew Carol’s] Lego drawing machine. He drew inspiration from the film Hugo and from automata of the 1800’s, specifically [Jaquet-Droz]’s Draughtsman, which we featured in a Retrotechtacular article not too long ago.

[Andrew’s] hand-cranked creation is divided into three components: a plotter, an “encoded pen stroke program”—which stores messages in links of pieces—and a reader that translates the links into pen strokes. The plotter moves the pen in the Y axis and moves the paper in the X to mark on the page, and also has a simple lift mechanism that temporarily raises the pen on the Z axis to interrupt pen strokes between letters (or drawings).

[Andrew] describes the chain reader by comparing it to a film projector, feeding the message through the mechanism. Although you won’t find a detailed how-to guide explaining the devices’ inner-workings on his site, there are some clues describing basic components and a couple of videos, both of which are embedded below.

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Acoustic Delay Line Memory

Back in the olden days  when computers were both analog and digital, making RAM was actually very hard. Without transistors, the only purely electronic means of building a memory system was vacuum tubes; It could have been done, but for any appreciable amount of RAM means an insane amount of tubes, power, and high failure rates.

One of the solutions for early RAM was something called a delay line. This device used ultrasonic transducers to send a pulse through a medium (usually mercury filled tubes heated to 40°C) and reads it out at the other end. The time between the pulse being sent and received is just enough to serve as a very large, small capacity RAM.

Heated tubes filled with hundreds of pounds of mercury isn’t something you’d want sitting around for a simple electronics project. You can, however, build one out of a Radio Shack Electronics Learning Lab, a speaker, and a microphone.

[Joe] designed his delay line using an op-amp to amplify the train of acoustic pulses traveling through the air. A compactor picks up these pulses and sends them into a flip-flop. A decade counter and oscillator provide the timing of the pulses and a way to put each bit in the delay line. When a button on the electronics lab is pressed, a ‘tick’ is sent into the speaker where it travels across [Joe]’s basement, into the microphone, and back into the circuit.

The entire setup is able to store ten bits of information in the air, with the data conveniently visualized on an oscilloscope. It’s not a practical way to store data in any way, shape, or form, but it is an interesting peek into the world before digital everything.

Video below.

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Overhauling An IC Programmer

Willem IC Programmer

[NeXT] needed an EPROM programmer to work with chips from vintage computers. Starting with a low cost programmer, he built this custom IC programmer to handle all of his programming needs.

The device is based on the Willem 5.0e programmer. [NeXT] was not satisfied with the device, noting that it had to be carefully isolated from metal surfaces during use and required setting many annoying jumpers.

To solve these problems, he started off by dismantling the programmer. The IC sockets were moved to a daughter board, which could be mounted cleanly into the metal enclosure. Replacing the jumpers was a bit more complicated, a combination of toggle and rotary switches were chosen to make changing settings easier.

Soldering the boards together looks like it was not an easy task, with 200 solder joints needed to connect the sockets and switches. After debugging some shorts and dead connections, [NeXT] managed to finish the 1.5 year project right before his Christmas deadline.

The Most Beautiful Floppy Disk Jukebox Ever

Playing music on floppy drives is something that has been done to death. [kiu]’s RumbleRail is something else entirely. Yes, it’s still a collection of floppy drives playing MIDI files, but the engineering and build quality that went into this build puts it in a class by itself.

Instead of the usual assemblage of wires, power cords, and circuits that accompany most musical floppy drive builds, [kiu]’s is an exercise in precision and modularity. Each of the eight floppy drives are connected to its own driver with an ATMega16 microcontroller on board. The microcontrollers in these driver boards receive orders from the command board over an I2C bus. Since everything on the RumbleRail is modular, and the fact [kiu] is using DIP switches to set the I2C address of each board, this build could theoretically be expanded to 127 voices, or 127 individual floppy drives each playing their part of a MIDI file.

The RumbleRail can also operate in a standalone mode without the need for a separate computer feeding it data. MIDI files can be loaded off an SD card by the main controller board, and decode them for the floppy drivers.

If you’d like to build your own RumbleRail, all the board files, schematics, and firmware are up on [kiu]’s git. There are, of course, a few videos below of the floppy jukebox in action.

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[Fran]’s LEDs, Nixies, And VFDs.

FRAN LED

With a love of blinky and glowey things, [Fran] has collected a lot of electronic display devices over the years. Now she’s doing a few teardowns and tutorials on some of her (and our) favorite parts: LEDs and VFD and Nixie tubes

Perhaps it’s unsurprising that someone with hardware from a Saturn V flight computer also has a whole lot of vintage components, but we’re just surprised at how complete [Fran]’s collection is. She has one of the very first commercial LEDs ever made. It’s a very tiny red LED made by Monsanto (yes, that company) packaged in a very odd lead-and-cup package.

Also in her LED collection is a strange Western Electric part that’s green, but not the green you expect from an LED. This LED is more of an emerald color – not this color, but more like the green you get with a CMYK process. It would be really cool to see one of these put in a package with red, green, and blue LED, and could have some interesting applications considering the color space of an RGB LED.

Apart from her LEDs, [Fran] also has a huge collection of VFD and Nixie tubes. Despite the beliefs of eBay sellers, these two technologies are not the same: VFDs are true vacuum tubes with a phosphorescent coating and work something like a CRT turned inside out. Nixies, on the other hand, are filled with a gas (usually neon) that turns to plasma when current flows through one of the digits. [Fran] has a ton of VFDs and Nixies – mostly military surplus – and sent a few over to [Dave Jones] for him to fool around with.

It’s all very cool stuff and a great lead-in to what we hear [Fran] will be looking at next: electroluminescent displays found in the Apollo Guidance Computer.

Videos below.

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Build An Audio Spectrum Analyzer The Analog Way

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[Ryan] wanted a spectrum analyzer for his audio equipment. Rather than grab a micro, he did it the analog way. [Ryan] designed  a 10 band audio spectrum analyzer. This means that he needs 10 band-pass filters. As the name implies, a band-pass filter will only allow signals with frequency of a selected band to pass. Signals with frequency above or below the filter’s passband will be attenuated. The band-pass itself is constructed from a high pass and a low pass filter. [Ryan] used simple resistor capacitor (RC) filters to implement his design.

All those discrete components would quickly attenuate [Ryan’s] input signal, so each stage uses two op-amps. The first stage is a buffer for each band. The second op-amp, located after the band-pass filters, is configured as a non-inverting amplifier. These amplifiers boost the individual band signals before they leave the board. [Ryan] even added an “energy filler” mode. In normal mode, the analyzer’s output will exactly follow the input signal. In “energy filler” (AKA peak detect) mode, the output will display the signal peaks,  with a slow decay down to the input signal. The energy filler mode is created by using an n-channel FET to store charge in an electrolytic capacitor.

Have we mentioned that for 10 bands, all this circuitry had to be built 10 times? Not to mention input buffering circuitry. With all this done, [Ryan] still has to build the output portion of the analyzer: 160 blue LEDs and their associated drive circuitry. Going “all analog” may seem crazy in this day and age of high-speed micro controllers and FFTs, but the simple fact is that these circuits work, and work well. The only thing to fear is perf board solder shorts. We think debugging those is half the fun.

Reverse Engineering HitClips

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After a quick review of the Hackaday viewer demographics, we need to say the late 90s were weird. Even portable audio players were downright bizarre: MP3 players existed, but you loaded up your songs (all eight of them) over your PC’s parallel port.  While helping a cousin move some furniture, [Ch00f] found a huge collection of one of the oddest music formats ever: HitClips, a tiny plastic encapsulated bit of circuitry that stores 60 seconds of terrible-sounding mono audio. Yes, this was a thing, but so was the pet rock. With no HitClips player, [Ch00f] decided he would take a swing at reverse engineering these tiny, tinny songs.

After taking apart the plastic enclosure, [Ch00f] found a very simple circuit: a few resistors, a cap, and an epoxy blob that enclosed an die with the musical data. On the back of the clip, there are eight pads for connecting to the player. With nothing to go on, [Ch00f] started poking around and found connecting one of these pins to ground caused circuit to draw 300uA of current for about 60 seconds – the same length of time as the recorded sample.

[Ch00f] originally thought the HitClip would provide audio data over an SPI or other digital protocol. What he found was much more interesting: two of the pins on the HitClip correspond to the push and pull FETs of a class D amplifier. The audio on the HitClip is digital audio, but it’s encoded so it can directly drive an analog circuit. Pretty clever engineering for a happy meal toy, if you ask us.

After dumping this data with a logic analyzer, [Ch00f] turned all the values in to .WAV file. It was, amazingly, music. A little refinement to the process to nail down the timing resulted in a 60-second clip seen (heard?) after the break.

Since [Ch00f] doesn’t want to spend $40 on eBay for a vintage HitClips player, he’s right about at the limit of what he can reverse engineer out of these cheap, crappy music chips. He has put up all his documentation, though, so if you’re up for improving on [Ch00f]’s methods, have a go.

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