The trick is to set the 555 up in astable mode, and use diodes and a potentiometer in the charge/discharge loop. By hanging a diode off either side of a potentiometer, leading to the charge and discharge pins, and connecting the center lug to the main capacitor, you can vary the resistance seen by the capacitor during charge and discharge. By making charging take longer, you increase the pulse width, and by making discharge take longer, you reduce the pulse width. The actual frequency itself is determined largely by the capacitor and total resistance of the potentiometer itself.
This is a very old-school way to generate a PWM signal, which could be used to vary intensity of a light or make noise on a buzzer. However, in this case, the output of the 555 is connected to a MOSFET which is used to vary the speed of a computer fan motor.
Thanks to microcontrollers, RTC modules, and a plethora of cheap and interesting display options, digital clock projects have become pretty easy. Choose to base a clock build around a chip sporting a date code from the late 70s, though, and your build is bound to be more than run-of-the-mill.
This is the boat that [Fran Blanche] finds herself in with one of her ongoing projects. The chip in question is a Mostek MK50250 digital alarm clock chip, and her first hurdle was find a way to run the clock on 50 Hertz with North American 60-Hertz power. The reason for this is a lesson in the compromises engineers sometimes have to make during the design process, and how that sometimes leads to false assumptions. It seems that the Mostek designers assumed that a 24-hour display would only ever be needed in locales where the line frequency is 50 Hz. [Fran], however, wants military time at 60 Hz, so she came up with a circuit to fool the chip. It uses a 4017 decade counter to divide the 60-Hz signal by 10, and uses the 6-Hz output to turn on a transistor that pulls the 60-Hz output low for one pulse. The result is one dropped pulse out of every six, which gives the Mostek the 50-Hz signal it needs. Sure, the pulse chain is asymmetric, but the chip won’t care, and [Fran] gets the clock she wants. Pretty clever.
Sometimes the best way to get a hacker to do something is to tell them that they shouldn’t, or even better can’t, do it. Nothing inspires the inquisitive mind quite like the idea that they are heading down the road less traveled, if for nothing else to say that they did it. A thrown gauntlet and caffeine is often all that stands between the possible and the impossible.
Preparing the PCB for epoxy injection
So when [Drygol] heard a friend comment he had an old Atari 800 XL that was such poor shape it couldn’t be repaired, he took on the challenge of restoring the machine sight unseen. Luckily for us, his pride kept him from backing down when he saw the twisted and dirty mess of a computer in person. He’s started documenting the process on his blog, and while this is only the first phase of the restoration, the work he’s done already is impressive enough that we think you’ll want to follow him along on his quest.
There’s no word on what happened to this miserable looking Atari, but we wouldn’t be surprised if it was run over by a truck. The board was cracked and twisted, with some components missing entirely. The first step in this impossible restoration was straightening the PCB, which [Drygol] did by clamping it to some aluminum bar stock and heating the whole board up to 40C (104F) for a few days. Once the got most of the bend out, he used a small drill bit to put holes in the PCB laminate and inject epoxy to add some strength. It’s an interesting technique, and the results seem to speak for themselves.
Once the board was straight, he went through replacing blown passive components and broken chip sockets. All the ICs were pulled and treated to an isopropyl alcohol and acetone bath in an ultrasonic cleaner to get them looking like new again. The CPU was cooked and needed to get swapped out, but otherwise it was smooth sailing, and before long he had the machine booted up. While most would have been satisfied to just get this far, [Drygol] considers this to be the easy part.
He next straightened out the metal shielding with a mallet, sanded it down, and sprayed it with a new zinc coating. The plastic around the keyboard and the metal trim pieces were also removed, cleaned, and refinished where necessary. Rather than going for perfection, [Drygol] intentionally left some issues so the machine didn’t look 100% pristine. It’s supposed to be a functional computer, not a museum piece behind glass.
We’ll have to wait until the next entry in this series to see how he repairs the absolutely devastated case. Any rational person would just use a case from a donor machine, but we’ve got a feeling [Drygol] might have something a little more impressive in mind.
You’d be forgiven if you thought software defined radio (SDR) was a relatively recent discovery. After all, few outside of the hardcore amateur radio circles were even familiar with the concept until it was discovered that cheap USB TV tuners could be used as fairly decent receivers from a few hundred MHz all the way up into the GHz range. The advent of the RTL-SDR project in 2012 brought the cost of entry level SDR hardware from hundreds of dollars to tens of dollars effectively overnight. Today there’s more hackers cruising the airwaves via software trickery than there’s ever been before.
It must be everyone’s birthday today because [Ken Shirriff] has come out with a gift for us. He’s done another pass at reverse engineering the 76477 Space Invaders sound chip from the 1970s and found it’s full of integrated injection logic (I2L), making it a double treat: we get to explore the more of this chip which made sounds for so many of our favorite games, and we explore a type of logic which was to be the successor to TTL until CMOS came along.
I2L gate
This article has a similar shape to his last one, first introducing I2L, followed by showing us what it looks like on the die, and then covering the different functional elements which make heavy use of it. The first of these is the noise generator made up of a section of shift registers and a ring oscillator. That’s followed by a noise filter which doesn’t use I2L but does use current mirrors. And lastly, he talks about the mixer which mixes output from the noise generator and elements covered in his previous article, the voltage-controlled oscillator, and the super-low frequency oscillator. Oddly enough, and as he points out, it isn’t an analog mixer. Instead, it just ANDs together the various inputs.
[Ken’s] no stranger to putting dies under the microscope. Check out our coverage of his talk at the 2016 Hackaday SuperConference where he shows us the guts of such favorites as the Z80 and the 555 timer IC.
We love a good deep-dive on a specialized piece of technology, the more obscure the better. You’re getting a sneak peek into a world that, by rights, you were never meant to know even existed. A handful of people developed the system, and as far as they knew, nobody would ever come through to analyze and investigate it to find out how it all went together. But they didn’t anticipate the tenacity of a curious hacker with time on their hands.
[Eduardo Cruz] has done a phenomenal job of documenting one such system, the anti-piracy mechanisms present in the Capcom CPS2 arcade board. He recently wrote in to tell us he’s posted his third and final entry on the system, this time focusing on figuring out what a mysterious six pin header on the CPS2 board did. Hearing from others that fiddling with this header occasionally caused the CPS2 board to automatically delete the game, he knew it must be something important. Hackaday Protip: If there’s a self-destruct mechanism attached to it, that’s probably the cool part.
He followed the traces from the header connector, identified on the silkscreen as C9, back to a custom Capcom IC labeled DL-1827. After decapping the DL-1827 and putting it under the microscope, [Eduardo] made a pretty surprising discovery: it wasn’t actually doing anything with the signals from the header at all. Once the chip is powered up, it simply acts as a pass-through for those signals, which are redirected to another chip: the DL-1525.
[Eduardo] notes that this deliberate attempt at obfuscating which chips are actually connected to different headers on the board is a classic trick that companies like Capcom would use to try to make it harder to hack into their boards. Once he figured out DL-1525 was what he was really after, he was able to use the information he gleaned from his earlier work to piece together the puzzle.
It’s easy to get caught up in the excitement of creation as we’re building our latest widget. By the same token, it’s sometimes difficult to fully appreciate just how old some of the circuits we use are. Even the simplest of projects might make use of elements that were once a mess on some physicist’s or engineer’s lab bench, with components screwed to literal breadboards and power supplied by banks of wet-cell batteries.
One such circuit turns 100 years old in June, which is surprising because it literally is the building block of every computer. It’s the flip-flop, and while its inventors likely couldn’t have imagined what they were starting, their innovation became the basic storage system for the ones and zeros of the digital age.
