Behind The Pin: Logic Level Outputs

There is one thing that unites almost every computer and logic circuit commonly used in the hardware hacking and experimentation arena. No matter what its age, speed, or internal configuration, electronics speak to the world through logic level I/O. A single conductor which is switched between voltage levels to denote a logic 1 or logic zero. This is an interface standard that has survived the decades from the earliest integrated circuit logic output of the 1960s to the latest microcontroller GPIO in 2018.

The effect of this tried and true arrangement is that we can take a 7400 series I/O port on an 8-bit microcomputer from the 1970s and know with absolute confidence that it will interface without too much drama to a modern single-board computer GPIO. When you think about it, this is rather amazing.

It’s tempting to think then that all logic level outputs are the same, right? And of course they are from a certain viewpoint. Sure, you may need to account for level shifting between for example 5V and 3.3V families but otherwise just plug, and go, right? Of course, the real answer isn’t quite that simple. There are subtle electrical differences between the properties of I/O lines of different logic and microcontroller families. In most cases these will never be a problem at all, but can rear their heads as edge cases which the would-be experimenter needs to know something about.

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The Quick-Build PowerWall

Elon Musk isn’t just the greatest human being — he’s also a great inventor. He’s invented the reusable rocket, the electric car, and so much more. While those are fantastic achievements, Elon’s greatest invention is probably the PowerWall. The idea of a PowerWall is simple and has been around for years: just get a bunch of batteries and build a giant UPS for your house. Elon brought it to the forefront, though, and DIYers around the world are building their own. Thanks, Elon.

Of course, while the idea of building your own PowerWall is simple, the devil is in the details. How are you going to buy all those batteries? How are you going to connect them together? How do you connect it to your fuse box? It’s a systems integration nightmare, made even more difficult by the fact that lithium cells can catch fire if you do something wrong. [jehugarcia] is building his own PowerWall, and he might have hit upon an interesting solution. He’s built a modular system to store and charge hundreds of 18650 cells. It looks great, and this might be the answer to anyone wanting to build their own PowerWall.

Aside from acquiring hundreds of 18650 cells, the biggest problem in building a PowerWall is simply connecting all the cells together. This can be done with 3D printed battery holders, solder, and bus bars, with a few people experimenting with spot welding wires directly onto the cells. This project might be a better solution: it uses standard plastic battery holders easily acquired from your favorite Chinese retailer and a PCB to turn cells into a battery.

The design of this battery module consists of a PCB with sufficiently wide traces, an XT60 power connector, and a few headers for the balance connector of a charger. This is a seven cell setup, and in contrast to the hundreds of hours that go into making a PowerWall the old fashioned way, these modules can be assembled pretty quickly.

Testing of these modules revealed no explosions, and everything worked as intended. There was a problem, though: when drawing a high load, the terminals of these cheap battery connectors got up to 150°. That makes these modules unsuitable for high load applications like an e-bike, but it should be okay if you’re putting hundreds of these modules together to power your house. It might be a good idea to invest in some cooling, though.
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Ask Hackaday: Is There a Common Mechanical Parts Library?

Like many stories, this one started on the roof. This particular roof is located in Michigan and keeps the rain and snow off of the i3Detroit hackerspace. Being an old industrial building, things up on the roof can start getting creaky, and when an almighty screech started coming from one of the rooftop vents as it swiveled in the wind, Nate, one of the group’s coordinators, knew it was time to do something about it.

Previous attempts to silence the banshee with the usual libations had failed, so Nate climbed up to effect a proper repair with real bearings. He dug into the unit, measured for the bearing, and came down to order the correct items. That’s when it struck him: How many should I order? After all, bearings are useful devices, not just to repair a wonky vent but especially handy in a hackerspace, where they can be put to all sorts of uses. Would extra bearings be put to good use, or would they just sit on a shelf gathering dust?

That’s when Nate dropped us a line and asked a question that raises some interesting possibilities, and one which we couldn’t answer offhand: Is there a readily accessible online library of common mechanical parts?

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Memristors On A Chip Solve Partial Differential Equations

We were always taught that the fundamental passive components were resistors, capacitors, and inductors. But in 1971, [Leon Chua] introduced the idea of a memristor — a sort of resistor with memory. HP created one in 2008 and since then we haven’t really had the burning need to use one. In a recent Nature article, [Mohammed Zidan] and others discuss a 32 by 32 memristor array on a chip they call a memory processing unit. This analog computer on a chip is useful for certain kinds of operations that CPUs are historically not efficient at, including solving differential equations. Other applications include matrix operations used in things like machine learning and weather prediction. The paper is behind a paywall, although the usual places to find scholarly papers will probably have it soon.

There are several key ideas for using these analog elements for high-precision computing. First, the array is set up in a passive crossbar arrangement. In addition, the memristors are quantized so that different resistance values represent different numbers. For example, a memristor element that could have 16 different resistance values would allow it to operate as a base-16 digit.

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Monoprice Mini Converted to Pick and Place (Kinda)

Would you believe that you can take a cheap 3D printer and easily convert it into a full function pick and place machine to help assemble your PCBs? No? Well good, because you can’t. A real pick and place needs all kinds of sensors and logic to identify parts, rotate them, make sure everything is aligned, etc, etc. There’s no way you could just bolt all that onto a cheap 3D printer, and let’s not even talk about the lack of closed loop control.

But if you have a very specific use case, namely a PCB that only has a relatively large single part that doesn’t need to be rotated, [Connor Nishijima] might have a solution for you. He bought a $150 USD Monoprice Mini, and with the addition of a few printed parts, was able to build a machine that drastically cuts down the time it takes for him to build his LED boards. Best of all the modification doesn’t involve any permanent changes to the printer, he can just pop off the vacuum attachment when he wants to print something.

Beyond the 3D printed parts (which were made on the printer itself), the only thing you need to make the modification is the vacuum pump. [Connor] is using a hot air station that includes a vacuum pump for picking up SMD components, but he mentions that you’d probably better off just modifying an aquarium pump and using that. A printed holder snaps over the cooling fan of the Monoprice Mini to hold the vacuum pickup tool, and another printed piece holds the strip of LEDs and the PCB. It’s worth noting that the machine has no ability to control the vacuum pump, and doesn’t need to. The pickup tool is so weak that when the LED lands in the solder paste it sticks to the board well enough that the tool can’t lift it back off.

The real genius in this build comes from the manually written G-Code. You load it from the printer’s built in menu system as if it was a normal 3D print, and it instructs the printer to move the vacuum tool over the line of LEDs, pick one up, and drop it in place on the PCB. It then uses a small peg built into the vacuum tool holder to advance the line of LEDs before starting the cycle all over again. Incredibly, it does this whole complex dance 20 times for each PCB without ever having any kind of feedback or alignment check. It only works because [Connor] was willing to go through the trial and error of getting the calibration and G-Code down as close to perfect as can be expected for such a cheap machine.

This isn’t the first time we’ve seen the Monoprice Mini converted into something a bit more impressive than a cheapo 3D printer. Seems that for whatever the machine lacks in the printing department, it more than makes up for in hackability.

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The PT2399 Delay/Echo Chip Data Sheet You Never Had

If you are fortunate enough to have had the opportunity to play with an analogue-reel-to-reel tape recorder in a well-equipped studio, you probably looped the tape around to create an echo, or a delay in the audio. It was a desirable effect to have, but not a practical one for a guitar pedal or similar portable accessory. Silicon alternatives for creating delays have been in production since the 1960s, first the so-called bucket brigade delay lines that used a switched chain of on-chip capacitors, and more recently all-digital chips that process the delay by storing samples in RAM. One of the more popular of those is the Princeton Technology PT2399, but it comes with something of a snag for the experimenter in the form of a sparse data sheet. Thankfully the folks at [Electrosmash] have come to the rescue on that front with a thorough technical examination of the chip that should fill in any gaps in the official documentation.

After a brief examination of the range of chips of which the 2399 is a part, they dive right into the chip’s internals by rearranging the internal circuit diagram from the data sheet to the point at which it makes more sense. At which point the difference between the chip’s delay and echo functions becomes obvious, through the inclusion of a feedback path.

We then are taken through the pins, examining what lies behind the power supply and analog inputs and outputs. We are somewhere between a data sheet and an app note here, as some of this is information rarely present even in really good data sheets. Finally, we are taken through the chip’s performance, with real-world distortion and noise measurements. Armed with this page, the would-be PT2399 designer really can say they know what they are working with.

Surprisingly few PT2399s have appeared on these pages, however one did pop up in the Synthbike.

Ken Shirriff Found Butterflies In His Op-Amp

In 1976, Texas Instruments came out with the TL084, a four JFET op-amp IC each with similar circuitry to Fairchild’s very popular single op-amp 741. But even though the 741 has been covered in detailed, when [Ken Shirriff] focused his microscope on a TL084, he found some very interesting things.

JFETs on the TL084 op-amp

To avoid using acid to get at the die, he instead found a ceramic packaged TL084 and pried off the cover. The first things he saw were four stabilizing capacitors, by far the largest structures on the die and visible to the naked eye.

When he peered into his microscope he next saw butterfly shapes which turned out to be pairs of input JFETs. The wide strips are the gates and the narrower strip surrounded by each gate is the source. The drain is the narrow strip surrounding each gate. Why arrange four JFETs like this? It’s possible to have temperature gradients in the IC, one side being hotter than the other. These gradients can affect the JFET’s characteristics, unbalancing the inputs. Look closely at the way the JFETs are connected and you’ll see that the top-left one is connected to the bottom-right one, and similarly for the other two. This diagonal cross-connecting cancels out any negative effects.

[Ken’s] analysis in his article doesn’t stop there though. Not only does he talk more about these JFETs but he goes over the rest of the die too. It’s well worth the read, as is his write-up about the 741 which we’ve also covered.