Stick Your Own Samples In The Cheetah SpecDrum

The Sinclair ZX Spectrum was a popular computer in the 8-bit era, and particularly so in its homeland of the United Kingdom. It was known more for its low cost than its capabilities, but it gained many add-ons over the years. One of those was the Cheetah SpecDrum, which turned the Spectrum into a rudimentary drum machine. [PianoMatt] wasn’t happy with the original drum samples, so he set about loading a custom kit into the SpecDrum.

The SpecDrum software initially came with extra sample tapes, so [PianoMatt] knew it was an achievable task to load in custom samples. Starting by loading the software in an emulator, the RAM was then exported as raw data and loaded up in Audacity. After some experimentation, it was determined the samples were stored in 8-bit format at a sample rate of approximately 20 kHz. With this figured out, it was then possible to load replacement samples directly into RAM through the emulator.

However, this wasn’t enough for [PianoMatt]. Further digging enabled him to reverse engineer the format of the replacement sample tapes. Armed with this knowledge, [PianoMatt] then generated his own tape, complete with proper headers and labels for each drum sound.

It’s a tidy effort to bring a more modern sound to a now positively ancient piece of hardware. We’d love to hear a track with drums courtesy of the SpecDrum, so we’ll keep an ear out on Soundcloud. Mucking around with old sound hardware is a popular pastime in these parts – we’ve even seen people go so far as to build bespoke Sega chiptune players from scratch. 

Design Tips For Easier CNC Milling

CNC machining is a wonderful thing, taking away a lot of the manual work required in machining and replacing it with accurate, repeatable computer control. However, this doesn’t mean that you can simply click a few buttons and become a great machinist overnight. There are a wide variety of skills involved in utilizing these tools effectively, and [Adam Bender] has created a guide to help budding makers learn the skills of design for CNC milling. 

[Adam]’s guide starts from a basic level, considering 3-axis CNC milling with the most commonly used tools. From there, a whole range of tips, tricks, and potential pitfalls are discussed to help new machinists get to grips with CNC milling. Everything from dogbone corners, to tool selection and feature heights are covered, as well as cost-saving techniques like minimising the number of setups required.

These are skills any engineer will learn in a hurry when approaching an experienced CNC machinist, but it’s always better to go in forewarned and forearmed. Of course, for those eager to not just work with, but build their own CNC machine, we’ve covered that base too. Video after the break.

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Using a Cheap Handheld Radio As A Morse Transceiver

Both grizzled hams and potential future amateur radio operators are well-served by the market these days. Powerful and capable UHF and VHF handheld transceivers can now be had for well under $100, something unimaginable as recently as 20 years ago. Of course, a major part of the amateur radio scene used to be Morse code. Not to worry though, you can do that with a handheld, too!

The setup is simple but effective. A Morse code training unit generates tones in response to input from a Morse keyer. This audio is passed into the headset port of a Baofeng handheld transmitter. A toggle switch is wired up to the Push-To-Transmit circuit of the Baofeng to trigger transmission when required.

It’s a little different from the more typical constant-wave transmission methods that are so seldom used nowadays, but it gets the job done. Morse code has always been appreciated in situations where voice transmission is difficult due to low bandwidth or interference, and now it’s easy for new hams to give it a try.

Morse code can be a trial to learn, but spare a thought for the folks who had to pick it up back in 1939. Video after the break.

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Yet Another Concrete Speaker Build

Concrete is great if you feel like making something heavy on the cheap. [Marek Unger] decided to have a go, using the material to cast speaker cabinets for a home hi-fi rig (Youtube link, embedded below).

Initial attempts involved creating a laser-cut MDF outer mold, with a styrofoam core inside to be removed later. This was unsuccessful, and [Marek] developed the design further. The second revision used an inner core also made from lasercut MDF, designed to be left inside after casting. This inner mold already includes the mounting holes for the speaker drivers, making assembly easier too.

Once cast, the enclosures were fitted with Tang-Band W4-1320SIF drivers. These are a full-range driver, meaning they can be used without needing crossovers or other speakers to fill in the frequency range. Each cabinet weighs just over 10kg, and they’re ported for extra response in the lower frequency bands. Sound tests are impressive, and the rough-finished aesthetic of the final product looks great in [Marek]’s living room.

We’ve seen concrete used for all manner of projects, from furnaces to USB hubs. Video after the break.

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Concrete Speakers Are Attractive And Functional

In a lot of fields – motorsport, space exploration, wearables – lighter is better. But it’s not always the case. When you want to damp vibration, stop things moving around, and give things a nice weighty feel, heavier is the way to go. This is the case for things like machine tools, anvils, and yes – speakers. Using this philosophy, [SoundBlab] built a set of concrete speakers. (Youtube link, embedded below)

The concrete speaker enclsosures are sized for 3″ drivers, and were cast using two measuring jugs as the mold. This gave the final product a smooth and glossy surface finish, thanks to the surface of the plastic used. The concrete was also agitated during the casting process to minimise the presence of air bubbles in the mixture.

Once cast, the enclosures are fitted with plywood end caps which mount the Fountek FE85 speaker drivers. These are a full-range driver, meaning no cross-overs or other drivers are required. The speakers are then mounted on stands constructed from wood edging, which are stained in a contrasting colour for a nice aesthetic touch. Felt pads are placed on the base, and polyfill inside the enclosure to further minimise any unwanted vibrations.

The sound test confirms the speakers perform well, and they look great as a part of a lounge audio setup. We think they make an excellent pair of bookshelf speakers, which would be ideal for comfortable listening at moderate volume levels.

We’ve seen many speaker builds at Hackaday, from 3D-printed omnidirectional builds to the more classical designs. Video after the break.

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PokerBot Uses FPGA For Card Calculating Horsepower

Played against humans, Poker is a game as much about reading your opponent as it is about the cards you’re dealt. That doesn’t mean there aren’t certain mathematical ways to aid your decision making based on probabilities. In this vein, a group of students from Cornell’s ECE 5760 class built a pokerbot on an FPGA.

The bot uses the principle of Monte Carlo simulation to calculate the probabilities of an individual winning a hand of Limit Texas Hold’em. Calculating the entire set of possible hands is impractical, so in a Monte Carlo simulation a sample is calculated instead. By accelerating these calculations on an FPGA, the pokerbot is able to calculate 300,000 possible hands in just 150 ms, and present a probability of winning to the human player. This same calculation method is then used to make decisions for the computer players in the game, too.

The team report that the FPGA’s processing power brought a 10x speed up compared to their C++ program running on an Intel i7-6700HQ. The strong statistical calculations help to make the computer players engaging and realistic to play against.

It’s another great example of a project from Bruce Land’s classes, which are somewhat of a hotbed of development each year. Video after the break.

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Reupholstering A Couch, With No Prior Experience

Upholstery is a craft that dates back far longer than many we feature on Hackaday. It requires patience, attention to detail, and a series of specialised skills. If you fancy yourself to be like a young Jack White, you might have considered trying your hand at a piece or two. [darkpine] did just that, and the results are impressive.

The couch was sourced from an online bartering platform, and was in a sad and sorry state after years of use. According to the original owner, the couch was over 100 years old and had been passed down through several generations. Last reupholstered in the 1970s, it was in dire need of repair. Wooden trim was falling off, fabric was fading, and resident cats had been sure to leave their mark.

[darkpine] set about things the right way, stripping the couch back to its bare bones. Taking careful note of the original construction, diagrams were made to ensure the springs could be retied in the correct fashion. Fresh burlap was installed, followed by foam and a layer of cotton batting. Careful attention was then paid to the fabric covering, with hand stitching used along the arms to get an absolutely perfect pattern match along the seams. With the hard part done, the wood was then restored and waxed to a glorious shine.

The final results are astounding, especially when noting that this was [darkpine]’s first ever upholstery project. We don’t see a lot of this kind of thing around here, but it’s not completely unknown.

[via Reddit]