The KIM-1 Computer Minified

The KIM-1 wasn’t the first microcomputer available to computer hobbyists and other electron aficionados, but it was the first one that was cheap. It was also exceedingly simple, with just a 6502 CPU, a little more than 1k of RAM, 2k of ROM, a hexadecimal keypad and a few seven-segment displays. Still, a lot of software was written for this machine, and one of these boards can be found in every computer history museum.

[Oscar] thought the KIM-1 was far too cool to be relegated to the history books so he made his own. It’s not a direct copy – this one uses an Arduino for the brains, only breaking out some buttons, a pair of four-digit seven-segment displays, and the I2C and SPI pins on the ‘duino. The KIM-1 is emulated by the Arduino, allowing for the same interface as an original connected up to an old teletype, and [Oscar] got his hands on the original code for Microchess and the first 6502 disassembler from [Woz] and [Baum].

[Oscar] put the schematics for his version of the KIM-1 up, and has the PCBs up on SeeedStudio. If you’re looking for an awesome replica of a vintage computer and a nice weekend project, here ‘ya go.

Very Large Touchpads for Very Old Computers

Way back when most of our demographic was in diapers, engineering workstations had huge touchscreens for plotting drawings in CAD programs, drawing, and just about everything a Wacom tablet does today. Finding one of these touch pads now is a fool’s errand, more so than finding the computer it was attached to, but [Daniel] figured out a way to relive those days of large touchpads and old computers with a resistive touchscreen and an MSX computer (portuguese, google translatrix).

[Daniel] is using a touchscreen normally used for a monitor, and with the right bit of code on a PIC16F micro, pressure on the touchscreen can be translated into X and Y coordinates. Using the PIC was a great choice in this instance: it’s possible to multiplex ports on an ADC pin with a PIC, making the entire system extremely efficient and easy to calibrate.

After that, it’s just a matter of plugging the output of the microcontroller into the touchpad connector of the MSX and writing a few lines of BASIC to draw a point on the screen. Video below.

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Low-Voltage Tube Amp is Great for Beginners

If you ever wanted to build your own tube amplifier but you were intimidated by working with high voltages, [Marcel]‘s low-voltage tube amp design might spark your interest. The design operates with a B+ (plate) voltage of only 40v, making it less intimidating and dangerous than many other amps that operate over 300V. It’s also incredibly easy to build—the whole design uses only 11 components.

The amplifier is designed around the ECL82 tube, which includes both a triode and a pentode in one package. The ECL82 is practically an amplifier in a tube: it was designed for low-cost electronics like record players that needed to be as simple as possible. The triode in the ECL82 is used as a pre-amplifier for the incoming signal. The pentode is controlled with the pre-amplified signal and acts as a power amplifier.

[Marcel]‘s amplifier also uses a PY88 tube rectifier instead of semiconductor diodes, making it an entirely silicon-free design. Although [Marcel] hasn’t posted up detailed build instructions yet, his simple schematic should be all you need to get started. If you want some more background information about tube amps but you don’t know where to start, check out our post on basic tube amp design from earlier this year.

Flaming Jack-o’-lanterns Light up the Night

[misterdob] wanted to spice up his Halloween decor, so he built these flaming concrete jack -o’-lanterns to decorate his walkway. He started with the classic plastic jack-o’-lanterns that trick-or-treaters have been using to collect candy for years. [misterdob] filled the plastic pumpkins halfway with concrete mix, then dropped in metal coffee cans. He then filled the pumpkins up to the top with concrete, shaking them up a bit to avoid air pockets.

Once the concrete had set, [misterdob] cut away the plastic revealing nearly perfect concrete duplicates. He used acid stain to color his creations – though it looks like he missed a spot or two.

We have to disagree with [misterdob's] choice of fuels. In fact, we think he was out of his gourd when he picked gasoline for his flaming pumpkins. Seriously though, gasoline is a horrible choice for a fire pot like this for a multitude of reasons. Gas has a particularly foul odor and its fumes are explosive. If a Halloween prankster were to try kicking one of the pumpkins over, not only would they have a broken foot, they’d also be covered in burning gas.

Thankfully, the folks on [misterdob's] Reddit thread had better fuel suggestions – citronella torch cans with lamp oil and wicks, kerosene, or gel fuel would be better suited for these hot pumpkins.

If you still don’t believe how dangerous gas and its fumes can be, check out this video of a bonfire gone wrong (language warning).

A Graphics Card for a Homebrew Computer

One of [aepharta]‘s ‘before I die’ projects is a homebrew computer. Not just any computer, mind you, but a fabulous Z80 machine, complete with video out. HDMI and DisplayPort would require far too much of this tiny, 80s-era computer, and it’s getting hard to buy a composite monitor. This meant it was time to build a VGA video card from some parts salvaged from old equipment.

When it comes to ancient computers, VGA has fairly demanding requirements; the slowest standard pixel clock is 25.175 MHz, an order of magnitude faster than the CPU clock in early 80s computers. Memory is also an issue, with a 640×480, 4-color image requiring 153600 bytes, or about a quarter of the 640k ‘that should be enough for anybody.’

To cut down on the memory requirements and make everything a nice round in base-2 numbers, [aepharta] decided on a resolution of 512×384. This means about 100k of memory would be required when using 16 colors, and only about 24 kB for monochrome.

The circuit was built from some old programmable logic ICs pulled from a Cisco router. The circuit could have been built from discrete logic chips, but this was much, much simpler. Wiring everything up, [aepharta] got the timing right and was eventually able to put an image on a screen.

After a few minutes, though, the image started wobbling. [aepharta] put his finger on one of the GALs and noticed it was exceptionally hot. A heatsink stopped the wobbling for a few minutes, and a fan stopped it completely. Yes, it’s a 1980s-era graphics card that requires a fan. The card draws about 3W, or about two percent of a modern, high-end graphics card.

A Proof of Concept Flash Cart for the WonderSwan

Unless you’ve been to Japan or are fairly deep into the retro game collecting, you’ve probably never heard of the WonderSwan. It’s a handheld console, released after the Game Boy Color was beginning to show its age, and a bit before the introduction of the Game Boy Advance. It sold rather well in the only country it was released in, the game library is somewhat impressive, and there are quite a few homebrew games. Actually running these homebrew games is a challenge, though: each WonderSwan has a memory controller that maps the game ROM into the CPU’s memory. Without knowing how this controller chip works, the only way to run a homebrew cartridge is to turn on the machine with a real cart, go to the system menu, and swap the carts out. It turns out there’s a better solution, that includes programming CPLDs and looking at the output of a logic analyzer.

The first step towards [Godzil]‘s efforts to create a Flash cart for the WonderSwan is to figure out the pinout of the cartridge connector – something that isn’t well documented for a system without a homebrew hardware scene. This was done in the usual way; with a lot of ribbon cable and patience This only provided an incomplete picture of how the WonderSwan interfaced with its carts, but after digging up an official development board, [Godzil] was able to make sense of all the signals.

After building a breakout board for the cartridge port, [Godzil] connected a DE0 Nano FPGA board and looked at all the signals. With just a little bit of VHDL, the memory controller could be reverse engineered and reimplemented. [Godzil] has his proof of concept working – video below – and the next part of his project will be to turn this into a proper Flash cart.

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Restoring A PDP-10 Console Panel

The PDP-10 was one of the first computers [Jörg] had gotten his hands on, and there are very, very few people that can deny the beauty of a panel full of buttons, LEDs, dials, and analog meters. When one of the front panels for a PDP-10 showed up on eBay, [Jörg] couldn’t resist; a purchase that would lead him towards repairing this classic console and making it functional again with a BeagleBone.

The console [Jörg] picked up is old enough to have voted for more than one Bush administration, and over the years a lot of grime has covered the beautiful acrylic panels. After washing the panel in a bathtub, [Jörg] found the dried panel actually looked worse, like an old, damaged oil painting. This was fixed by carefully scraping off the clear coat over two weeks; an important lesson in preserving these old machines. They’re literally falling apart, even the ones in museums.

With the front panel cleaned, [Jörg] turned his attention to the guts of this panel. The panel was wired up for LEDs, and each of the tiny flashlight bulbs in the pushbuttons were replaced. The panel was then connected to a BlinkenBone with a ton of wiring, and the SIMH simulator installed. That turns this console into a complete, working PDP-10, without sucking down kilowatts of power and heating up the room

This isn’t the first time we’ve seen [Jörg] with a BeagleBone and some old DEC equipment; earlier he connected the front panel of a PDP-11 variant to one of these adapters running the same software.