How To Tell If You’re Installing Foil Capacitors Backwards

It only takes one mistake to realize electrolytic capacitors have a polarity, but if you’re working with old tube gear, tube amps, or any old equipment with those old orange dip, brown dip, or green dip foil capacitors you also have to watch your polarity. These old caps were constructed with a foil shielding, and there’s always one side of these caps that should always be connected to the chassis ground. If you don’t, you’re going to get interference – not something you want in an amplifier circuit.

Old caps that have long since given up the ghost usually have a black band designating whatever side of the cap the ‘foil ground’ is. This is the side that should be connected to ground. If you look at modern foil caps, you might also see a black band on one side of the cap, which should – if we lived in a just world – also designate the foil ground. This is not always the case.

To properly test foil caps and determine which side should be closer to ground, you can construct a small tester box that’s more or less an h-bridge with a single switch and a pair of alligator clips in the middle. Connect the cap to the clips, put the output of the circuit in your scope, and flick the switch: the direction that has the least amount of interference is the denotes the foil ground of the cap. Replace those old caps in your vintage equipment with a new, correctly oriented cap, and you’re well on your way to having a great sounding amplifier.

Video below.

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Articulated Computer Lamp Lights up your life

[Samimy] raided his parts bin to build this articulated lamp (YouTube link) for his computer workstation. Two pieces of aluminum angle form the main body of the lamp. Several brackets are used to form two hinges which allow the lamp to be positioned above [Samimy’s] monitor. The light in this case comes from a pair of 4 watt LED bulbs.

[Samimy] used double nuts on the moving parts to make sure nothing comes loose. The outer nuts are acorns, which ensure no one will get cut on an exposed bit of threaded rod. [Samimy] wired the two bulbs up in a proper parallel mains circuit. The switch is a simple toggle mounted in a piece of Plexiglass on the end of the lamp.

One thing we would like to see on this build is a ground wire. With all that exposed aluminum and steel, one loose connection or worn bit of insulation could make the entire lamp body live.

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Vintage Computers At Maker Faire

It’s no secret that Maker Faire is highly geared toward the younger crowd. This doen’t mean the Faire is completely devoid of the historic; the Bay Area Maker Faire is right in the heart of the beginnings of the computer industry, and a few of the booths are showing off exactly how far computers have come over the last forty years.

Superboard[Vince Briel] of Briel Computers has a booth showing off his wares, mostly modern reimaginings of vintage computers. His table is loaded up with replica 1s, a board that’s much smaller but still completely compatible with the Apple I. The MicroKIM made an appearance, but the crown jewel is [Vince]’s Superboard III, a replica of the Ohio Scientific Superboard II. It’s your basic 6502 computer with 32k of RAM, but unlike just about every other modern retrocomputer out there, [Vince] put the keyboard right on the main board.

The switches are Cherry MX, the keys are from WASDkeyboards. [Vince] is actually getting a lot of interest in making modern ASCII keyboards to replace the old and busted boards that came in the home computers of the 70s and 80s. That might be a project [Vince] will release sometime in the future.

[Jef Raskin], the Swift Card, and the Canon Cat

[Steve Jobs] may have been the father of the Macintosh, but he was, by no means, solely responsible for the Mac. It was a team of people, and when you talk about the UI of the Mac, the first name that should come up is [Jef Raskin].

One of [Jef Raskin]’s finest works was the Swyft Card, an add-on to the Apple II that was basically just a ROM card that had an OS and Forth interpreter on it. The distinguishing feature of the Swyft card was the use of ‘leap’ keys, a simple way to change contexts when using the computer. We’ve seen replicas of the Swyft card before, courtesy of [Mike Willegal] at the Vintage Computing Festival East.

Woodie[Dwight Elvey] of the vintage-computer.com forum brought a few extra special items related to [Raskin] and the Canon Cat. The first was a Swyft card installed in an Apple IIe. The second was a prototype Swyft computer, with SERIAL NUMBER 1 printed on a Dymo label and fixed to the case.

The ‘woodie’, as [Dwight] calls it, has two 1.44 MB disk drives, of which half of the disk is actually usable. [Dwight] didn’t take the machine apart, but I’m 99% sure the CRT in it is the exact same tube found in early 9″ Macs.

Also in [Dwight]’s display is a production Swyft computer and a Canon Cat, the final iteration of [Jef Raskin]’s idea of what a text-based computer should be.

The vintage-computer booth also had a few interesting retrocomputers including a Commodore 128D, the Apple made, Bell & Howell branded Apple II, and an Amiga 2000. Right next door was the Computer History Museum, who brought a very kid-friendly storage medium display. Showing a 10-year-old an 8″ disk is fun.

Bicycle-Powered Wimshurst Machine

A lot of great pieces of real technology were inspired (or, at least, look like) pieces of technology from science fiction of the past. Like the smartphones of today have a surreal resemblance to the Star Trek communicators of the 60s, [Steve] took inspiration from a story about a bicycle racing in space and set out to make his own.

In the story, the bicycle wheels are replaced by electrostatic generators that power a type of (fictional) ion drive. Since an ion drive wouldn’t add much thrust to a bicycle operated on the Earth, [Steve] used the electrostatic generator he built to create a sparking light show. The generator is called a Wimshurst machine and has two counter-rotating discs which collect charge. The charge is dissipated across a spark gap which is placed where the bike light would normally go.

We don’t know if the sparks from the Wimshurst generator are enough for a proper headlight, but it’s definitely a cool effect. [Steve] also points out that it might also work as a bug zapper, but either way you should check out the video after the break to see it in action! While it’s not quite a tricorder it’s still a pretty impressive sci-fi-inspired build, and something that’s definitely unique in the bicycle realm.

There’s quite a collection of these Wimshurst projects beginning to come together. Here’s one made using a trio of soda bottles, and another example which used 3D printing.

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Robot K-9 Scares Off the Daleks

[Bithead942’s] love of the ever popular Dr Who series led her to develop a replica of the 4th Doctor’s robotic companion. It’s name is K-9, and was built from scratch in only 4 months. Its shell is made from HPDE – a light and bendable plastic. A custom plastic bender was constructed to get the angles just right, and custom laser cut parts were used in various places.

Its frame consists of aluminum channel, and is packed full of juicy electronics. An arduino with an XBee shield controls the remote voice, frickin’ laser and eye sensors. Another arduino is paired with a motor shield to control the linear actuator for the neck movement. And a Raspberry Pi keeps the LCD screen in order.

We’re not done, folks. Because this puppy is radio controlled, a custom controller is needed. Sparkfun’s Fio paired with another XBee is used along with a 16×2 LCD and various other electronics to keep the robot on an invisible leash.

Be sure to check out the blog site, as it goes into great detail on all the various parts used to construct this complicated but awesome project.

Hackaday Retro Edition: TRS Wiki

1977 was a special year for computing history; this year saw the release of the 8085 following the release of the Z80 a year before. Three companies would launch their first true production computers in 1977: Apple released the Apple II, Commodore the PET 2001, and Tandy / Radio Shack the TRS-80 Model I. These were all incredibly limited machines, but at least one of them can still be used to browse Wikipedia.

[Pete]’s TRSWiki is a Wikipedia client for the TRS-80 Model I that is able to look up millions of articles in only uppercase characters, and low resolution (128×48) graphics. It’s doing this over Ethernet with a very cool Model I System Expander (MISE) that brings the lowly Trash-80 into the modern era.

The MISE is capable of booting from CF cards, driving an SVGA display and connecting to 10/100 Ethernet. Connecting to the Internet over Ethernet is one thing, but requesting and loading a web page is another thing entirely. There’s not much chance of large images or gigantic walls of text fitting in the TRS-80’s RAM, so [Pete] is using a proxy server on an Amazon Web Services box. This proxy is written in Java, but the code running on the TRS-80 is written entirely in Z80 assembly; not bad for [Pete]’s first project in Z80 assembly.


vt100normal The Hackaday Retro Edition is our celebration of old computers doing something modern, in most cases loading the old, no CSS or Javascript version of our site.

If you have an old computer you’d like featured, just load up the retro site, snap some pictures, have them developed, and send them in.

Extreme Vectrex Multicart Plays Bad Apple

[Sprite_TM] had a Vectrex console that he wanted to play with. Alas, his makeshift multicart had fallen into disrepair. Rolling up his hacking sleeves, he set about making a new one, a better one. His PCB design included his microcontroller of choice: the ST STM32F411, a 32-bit 100Mhz ARM Cortex M4, along with a 16MB SPI flash chip. [Sprite_TM] wanted to make programming games onto the multicart simple. Using the libopencm3 firmware library for the STM in conjunction with Elm-Chans FatFS, the multicart could be plugged into a computer’s USB port and have any game data dragged and dropped onto it like a USB stick. The PCB then connects directly into the Vectrex’s cartridge port. The first cartridge file is a basic menu that lists all of the game ROMs stored in the flash memory. When the user selects the game the STM loads that ROM file which the menu software then boots.

After loading his entire Vectrex ROM library onto the multicart, [Sprite_TM] realized he had far too much space left over – so he decided to add some extras. His first choice was Bad Apple (YouTube link), a music video made by fans of the Touhou Project game series. The video features black and white silhouettes of the many game characters in a shadow art style. Since its debut, Bad Apple has been ported from everything from the Sega Genesis (YouTube link) to laser scanners (YouTube link). It was time for the Vectrex to join the list.

After ripping the video from YouTube, [Sprite_TM] used MPlayer to save each frame as a PNG along with a wave file of the music. Next, he ran Potrace on the PNG files to get vector versions. Using a custom PHP script, the resulting JSON file was post-processed into relative vectors the Vectrex uses. Digital audio was possible by having the Vectrex’s 8-bit DA-converter perform double duty both for the video circuit and the audio. However, the volume must be turned to the max in order to hear the music. Incidentally, the DAC can only output audio in this scenario when vectors are not being drawn, so the event timing needed to be adjusted. The video and audio data was re-parsed after a modified version of VecX was used to get the timing events synchronized before transferring Bad Apple onto the multicart.

You can see the Vectrex version of Bad Apple after the break, along with a 3D-engine based on Doom levels. The engine is written in C and makes use of the Z-buffer, creating the effect of solid 3D-objects in front of each other.  There are no weapons or enemies to dispatch here, but the effect is impressive nonetheless.

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