Making 128MB SIMMs From Junk

simm

Working for a tech repair/recycling center, [Jax] has access to a ton of cool hardware. Most of it is junk, but that’s just the way he likes it. Among his better finds in the depths of a tech treasure trove is a huge antistatic bag of 64 MB 72 pin SIMMs. These were the standard RAM form factor for just about everything in the 90s, and while 64 MB is a huge amount of RAM for the time, they’re still a bit away from the 72 pin max of 128 MB.

After inspecting these sticks, [Jax] noticed something odd. Each side had pads for memory chips, but only one side was populated. Given the rarity of 128 MB sticks of RAM, [Jax] decided he would have a go at adding 64 Megs of RAM to these chips by desoldering one stick and sticking it on the back of another.

These new 128 MB SIMMs made their way into a Macintosh Quadra 605 for testing. While the 64 MB chips worked fine, the new 128 MB chips threw a chime of death. Something was terribly wrong.

While investigating, [Jax] couldn’t find any bridged solder joints, and everything looked okay. Heat is a wonderful test of what went wrong, and with the SIMM connected to a power source, he found all of the newly transplanted chips were hot. Because the chips on back side of the SIMMs were meant to be installed upside down, [Jax] had inadvertently connected the ground to power and power to ground.

Fixing his mistake on a new SIMM, [Jax] popped it in his old Mac and tried booting with these SIMMs again. There wasn’t a chime of death, but booting with these chips took a very long time. This was actually just the Mac checking all the RAM, which was successfully addressed once [Jax] finally booted his OS.

Testing DRAM From a Commodore 64

dram

A few months ago, [Josh] was given an old Commodore 64. He needed to make an AV cable and find a new power supply, and even after testing these new parts out, [Josh] found it still wouldn’t boot. Not one to look a gift horse in the mouth — or perhaps he enjoys the challenge — he set out on restoring a thirty year old circuit board.

He replaced a few chips and the caps, but found he had no way to test the DRAM chips. Compared to SRAM or Static RAM used by other computers of the era, DRAM is a bit harder to interface, requiring a capacitor in each memory cell to be refreshed a few dozen times every second. With a bit of help from his good friend [CNLohr], [Josh] figured out a circuit to read and write to his chips and build a small board based on the ATmega8U2 microcontroller for testing purposes.

Drive bay form factor dual Dekatron readouts for RAM and CPU usage

optical-drive-dual-dekatron

The two circular displays seen above are Dekatrons built into an optical drive enclosure. [Matt Sylvester] picked up a couple of different types of these tubes on eBay. He etched his own driver, and was able to control them with an Arduino. After a few months went by he decided to revisit the project to see if it would work as a CPU and RAM usage meter.

These tubes need high voltage to get the neon display glowing brightly. This raised some concerns about having those voltage levels inside of his PC, as well as the noise which may be introduced by the supply. To deal with those issues [Matt] gutted an old optical drive, using its case to physically isolate the circuitry, and some optoisolators to protect the logic connections. His driver board uses an ATmega328 running the Arduino bootloader. It connects to the PC using an FTDI USB to Serial cable. This makes it a snap to push the performance data to the display. It also has the side benefit of allowing  him to reprogram the chip without opening the case.

If you can’t find one of these tubes for your own project consider faking it.

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Building RAM into Veronica – the 6502 computer

ram-for-veronica

It seems strange that RAM is being added to a computer so late in the build, but [Quinn Dunki] must have had it in the back of her mind the whole time because it turns out to be a rather painless experience. For those of you keeping score, this makes her Veronica project Turing complete.

The brightly colored rats nest pictured above connects the new components to the 6502 computer backplane seen in the upper left. [Quinn] decided to go with two 32K SRAM modules which need very little in the way of drive hardware (it’s hanging out on the breadboard to the left). The RAM module will simply listen for its address and react accordingly. There is one hitch regarding a two-phase clock and the need to protect the RAM from erroneous data during the first of those phases.

Getting this all to work actually pointed out a bug in the ROM module she had long ago completed. After picking up on the problem she was able to correct it simply by cutting traces and soldering in jumper wires.

Extending old games with reverse engineering and MAME

HEX

For last year’s Toorcamp, the folks over at DorkbotPDX helped out with the Church of Robotron installation. A religion founded on the prophesy of a cybernetic uprising in the year 2084 is a little esoteric even for us, so the Dorkbot crew wanted a way to make playing Robotron: 2084 a little more visceral. Using MAME and a few debugging tools, they were able to read the memory of a machine playing Robotron to extend the game into the physical world. When the player dies, lights go off, alarms sound, and the prophet of the Church of Robotron is pleased.

The setup at the Church of Robotron included a machine running MAME with a Robotron ROM. When events happened in the game, such as lasers firing or a player death, physical events would be triggered. To do this, the Dorkbot team read the memory locations of a game of Robotron at different times and found memory locations tied to in-game events. On their blog they go over using the MAME debug tool to detect a player’s death which can then be translated into physical apparitions for the Church of Robotron.

It’s a very cool hack, and one we wish we had a video of. Having a plastic ghost hit a player while playing Pac-Man seems like an awesome idea, and with the Dorkbot tutorial, it looks fairly easy.

Raspis with double the RAM in the wild

There is buzz all over the reddits and Element 14 discussion boards about an updated version of the Raspberry Pi that bumps the amount of RAM from 256 MB to 512 MB.

This new update comes after the announcement of an upgraded version of the yet-to-be-released Raspi Model A (from 128 MB of RAM to 256 MB), and a few slight modifications to the Model B that include fixing a few hardware bugs (nothing serious) and adding mounting holes.

After perusing the Element 14 and Raspberry Pi discussion boards, a few things become apparent. Firstly, it appears this new upgrade to double the amount of RAM was initiated by manufacturers. It seems 512 MB RAM chips are cheap enough now to include in the Raspi without impacting the cost of components. Secondly, 512 MB seems to be the upper limit for the Raspberry Pi, at least for this iteration of hardware. Not enough address lines, they say, but you’re welcome to try and hack your own RAM to a Raspi CPU.

So far, attentive Raspi enthusiasts have found Raspberry Pis with double the amount of RAM on the UK Farnell site and the Australian Element 14 site. Nothing so far on the US Element 14 site, although we’ll gladly update this post when a Hackaday reader finds the relevant link.

EDIT: Here’s the link for the US version of Newark. No, there aren’t any in stock. Also, Hackaday beat the official Farnell/Element 14/Newark press release and the Raspberry Pi blog to the punch. Woo, go us.

Playing around with MRAM

For the longest time, hardware tinkerers have only been able to play around with two types of memory. RAM, including Static RAM and Dynamic RAM, can be exceedingly fast but is volatile and loses its data when power is removed. Non-volatile memory such as EPROMS, EEPROMS, and Flash memory retains its state after power is removed, but these formats are somewhat slower.

There have always been competing technologies that sought to combine the best traits of these types of memory, but not often have they been available to hobbyists. [Majenko] got his hands on a few MRAM chips – Magneto-Resistive RAM – and decided to see what they could do.

Magneto-Resistive RAM uses tiny pairs of magnetic plates to read and write 1s and 0s. [Majenko] received a sample of four MRAM chips with an SPI bus (it might be this chip, 4 Megabits for $20, although smaller capacity chips are available for about $6). After wiring these chips up on a home-made breakout board, [Majenko] had 16 Megabits of non-volatile memory that was able to run at 40 MHz.

The result was exactly what the datasheet said: very fast write and read times, with the ability to remove power. Unlike EEPROMS that can be destroyed by repeated reading and writing, MRAM has an unlimited number of write cycles.

While MRAM may be a very young technology right now, it’s a wonderful portent of things to come. In 20 (or 30, or 40) years, it’s doubtful any computer from the largest server to the smallest microcontroller will have the artificial separation between disk space and memory. The fact that any hardware hacker is able to play around with this technology today is somewhat amazing, and we look forward to more builds using MRAM in the future.