In the days before every piece of equipment was an internet-connected box with an OLED display, engineers had to be a bit more creative with how they chose to communicate information to the user. Indicator lights, analog meters, and even Nixie tubes are just a few of the many methods employed, and are still in use today. There are, however, some more obscure (and arguably way cooler) indicators that have been lost to time.

[Aart Schipper] unearthed one such device while rummaging around in his father’s shed: a pair of Burroughs Bar Graph Glow-Transfer Displays. These marvelous glowing rectangles each have two bars (think the left and right signals on an audio meter, which is incidentally what they were often used for), each with 201 neon segments. Why 201, you may ask? The first segment on each bar is always illuminated, acting as a “pilot light” of sorts. This leaves 200 controllable segments per channel. Each segment is used to “ignite” its neighboring segment, something the manufacturer refers to as the “Glow-Transfer Principle.” By clever use of a three-phase clock and some comparators, each bar is controlled by one analog signal, keeping the wire count reasonably low.

Don’t get us wrong, the warm, comforting glow of Nixie tubes will always have a special place in our hearts, but neon bar graphs are just hard to beat. The two do have a similar aesthetic though, so here’s hoping we see them used together in a project soon.

Thanks to [Jan] for the tip!

In retrocomputing circles, it’s often the case that the weirder and rarer the machine, the more likely it is to attract attention. And machines don’t get much weirder than the DEC Rainbow 100-B, sporting as it does both Z80 and 8088 microprocessors and usable as either a VT100 terminal or as a PC with either CP/M or MS-DOS. But hey — at least it got the plain beige box look right.

Weird or not, all computers have at least a few things in common, a fact which helped [Dr. Joshua Reichard] home in on the problem with a Rainbow that was dead on arrival. After a full recapping — a prudent move given the four decades since the machine was manufactured — the machine failed to show any signs of life. The usual low-hanging diagnostic fruit didn’t provide much help, as both the Z80 and 8088 CPUs seemed to be fine. It was then that [Joshua] decided to look at the heartbeat of the machine — the 24-ish MHz clock shared between the two processors — and found that it was flatlined.

Unwilling to wait for a replacement, [Joshua] cobbled together a temporary clock from an Arduino Uno and an Si5351 clock generator. He connected the output of the card to the main board, whipped up a little code to generate the right frequency, and the nearly departed machine sprang back to life. [Dr. Reichard] characterizes this as a “defibrillation” of the Rainbow, and while one hates to argue with a doctor — OK, that’s a lie; we push back on doctors all the time — we’d say the closer medical analogy is that of fitting a temporary pacemaker while waiting for a suitable donor for a transplant.

This is the second recent appearance of the Rainbow on these pages — [David] over at Usagi Electric has been working on the graphics on his Rainbow lately.

The 16×2 LCD display is a classic in the microcontroller world, and for good reason. Add a couple of wires, download a library, mash out a few lines of code, and your project has a user interface. A utilitarian and somewhat boring UI, though, and one that can be hard to read at a distance. So why not spice it up with these large-type custom fonts?

As [Vaclav Krejci] explains, the trick to getting large fonts on a display that’s normally limited to two rows of 16 characters each lies in the eight custom characters the display allows to be added to its preprogrammed character set. These can store carefully crafted patterns that can then be assembled to make reasonable facsimiles of the ten numerals. Each custom pattern forms one-quarter of the finished numeral, which spans what would normally be a two-by-two character matrix on the display. Yes, there’s a one-pixel wide blank space running horizontally and vertically through each big character, but it’s not that distracting.

Composing the custom patterns, and making sure they’re usable across multiple characters, is the real hack here, and [Vaclav] put a lot of work into that. He started out in Illustrator, but quickly switched to a spreadsheet because it allowed him to easily generate the correct binary numbers to pass to the display for each pattern. It seems to have really let his creative juices flow, too — he came up with 24 different fonts! Out favorite is the one he calls “Tron,” which looks a bit like the magnetic character recognition font on the bottom of bank checks. Everyone remembers checks, right?

Hats off to [Vaclav] for a creative and fun way to spice up the humble 16×2 display. We’d love to see someone pick this up and try a complete alphanumeric character set, although that might be a tall order with only eight custom characters to work with. Then again, if Bad Apple on a 16×2 is possible…

There are a surprising wealth of parts inside of old laptops that can be easily scavenged, but often these proprietary tidbits of electronics will need a substantial amount of work to make them useful again. Obviously things such as hard drives and memory can easily be used again, but it’s also possible to get things like screens or batteries to work with other devices with some effort. Now, there’s also a way to reuse the trackpad as well.

This build uses a PS/2 touchpad with a Synaptics chip in it, which integrates pretty smoothly with an Arduino after a few pins on the touchpad are soldered to. Most of the work is done on the touchpad’s built in chip, so once the Arduino receives the input from the touchpad it’s free to do virtually anything with it. In this case, [Kushagra] used it to operate a stepper motor in a few different implementations.

If you have this type of touchpad lying around, all of the code and schematics to make it useful again are available on the project page. An old laptop in the parts bin is sure to have a lot of uses even after you take the screen off, but don’t forget that your old beige PS/2 mouse from 1995 is sure to have some uses like this as well.

There are plenty of techniques and components that we use in our everyday hardware work, for which their connection and coding is almost a done deal. We are familiar with them and have used them before, so we drop them in without a second thought. But what about the first time we used them, we had to learn somewhere, right? [TheMagicSmoke] has produced just what we’d have needed then for one component that’s ubiquitous, the I²C EEPROM.

These chips provide relatively small quantities of non-volatile memory storage, and though they are not the fastest of memory technologies they have a ready application in holding configuration or other often-read and rarely written data.

Since the ST24C04 512-byte device in question has an I²C bus it’s a straightforward add-on for an Arduino Mega, so we’re shown the wiring for which only a couple of pull-down resistors are required, and some sample code. It’s not the most complex of projects, but it succinctly shows what you need to do so that you too can incorporate an EEPROM in your work.

If learning about I²C EEPROMs piques your interest, perhaps you’d like to read a previous look we made at them.

We love to see projects undertaken for the pure joy of building something new, but to be honest those builds are a dime a dozen around here. So when we see a great build that also aims to enhance productivity and push an entrepreneurial effort along, like this automated small parts counter, we sit up and take notice.

The necessity that birthed this invention is [Ryan Bates’] business of building DIY arcade game kits. The mini consoles seen in the video below are pretty slick, but kitting the nuts, bolts, spacers, and other bits together to ship out orders was an exercise in tedium. Sure, parts counting scales are a thing, but that’s hardly a walk-away solution. So with the help of some laser-cut gears and a couple of steppers, [Ryan] built a pretty capable little parts counter.

The interchangeable feed gears have holes sized to move specific parts up from a hopper to a chute. A photointerrupter counts the parts as they fall into plastic cups on an 8-position carousel, ready for bagging. [Ryan] also has a manual counter for wire crimp connectors that’s just begging to be automated, and we can see plenty of ways to leverage both solutions as he builds out his kitting system.

While we’ve seen more than a few candy sorting machines lately, it’s great to see someone building hardware to streamline the move from hobby to business like this. We’re looking forward to seeing where [Ryan] takes this from here.

[Great Scott] should win an award for quickest explanation of a buck converter. Clocking in at five and a half minutes, the video clearly shows the operating principles behind the device.

It starts off with the question, what should you do if you want to drop a voltage? Many of us know that we can dim and brighten an LED using the PWM on an Arduino, but a closer inspection with an oscilloscope still shows 5V peaks that would be dangerous to a 3.3V circuit. He then adds an inductor and diode, this keeps the current from dropping too fast, but the PWM just isn’t switching fast enough to keep the coil energized.

A small modification to the Arduino’s code, and the PWM frequency is now in the kHz range. The voltage looks pretty good on the oscilloscope, but a filter cap gets it to look nice and smooth. Lastly, he shows how when the load changes the voltage out looks different. To fix this a voltage divider feeds back the information to the Arduino, letting it change the PWM duty to match the load.

In the last minute of the video he shows how to hook up off-the-shelf switching regulators, whose support components are now completely demystified as the basic principles are understood. Video after the break.

Today’s class went much better than last Friday’s.

I took the advice one of the students gave me last we and started with a “do now” question.  (She had actually suggested an “exit ticket”, but I don’t have the time management skills to leave a block of time at the end of class.)  The question I asked was a design task that was easy if you knew what you were doing, but subtly harder than the standard sort of text-book question, because it was a design question, not an analysis question:

You have sensor whose resistance varies from 1kΩ to 4kΩ with the property it measures.  Design a circuit whose output voltage varies from 1v (at 1kΩ) to 2v (at 4kΩ).

I gave the students 10 minutes to work on this at the beginning of class.  A good question to prompt discussion (according to the peer instruction blogs and websites) should be answerable by 30–80% of the students.  More than that and the question was too easy to be useful, and less than that and the question is too hard for peer discussion to be worthwhile.  It turned out that no one had gotten it after 10 minutes (too hard to use as a peer instruction question), so we used it as the basis for a class discussion.

Almost everyone realized that the desired circuit was a voltage source and a voltage divider (not too surprising, since that’s the only circuit they’ve used so far).  The majority also realized that the variable resistor had to be on the lower leg, between the output and ground, and a couple of the students could articulate why.  I suggested the common heuristic of trying extreme values (0 and ∞) for the variable resistor, to see whether the output voltage would go up or down as the resistance changed.

The students were then able to set up the simultaneous equations to solve for the input voltage and the fixed resistance.  The hole in everyone’s thinking when working on the problem initially is that they had not considered the voltage of the source as a design parameter to solve for, though one student had asked about it. This was the blind spot I was expecting, so I was able to use it as a teachable moment.  After we had the equations set up using mainly student input, I gave the students another minute or two to solve them, and about half the class was able to solve them correctly in the time provided. (I suspect that everyone could have if given enough time, but I didn’t want to take any more time in class—those who didn’t solve it in class could practice their algebra at home if they needed to.)  One student had made an algebra or arithmetic mistake, and gotten a source voltage smaller than one of the desired output voltages.  This was also a good mistake to get, since we could use it to talk about sanity checks on results.

I think that the 20 or so minutes of class was well spent, as we uncovered several important misconceptions, and raised awareness of all unspecified variables as potential design parameters, reasoning using extreme values, and the usefulness of sanity checks.

After that, we spent some time discussing different temperature sensors.  From the students, I got thermistor, infrared thermometer, mercury thermometer+camera, and enzyme + other sensor (pH, conductivity, color, …). I added RTD, silicon band-gap, and thermocouple to the mix.  We talked a little about the advantages and disadvantages of each. At the end, I also threw in bimetallic strips and tilt switches for one-bit digitization of temperature.  I wonder how many students will look at the thermostats in their apartments and try to figure out what sensor they include.

For the remainder of the class, we talked about gnuplot commands, particularly the “plot” command.

After class, several of us went over to the lab, where my son met us and helped the students install the DataLoger, python, pyserial, the Arduino environment, and gnuplot.  While he was doing that, I borrowed an Uno R3 Arduino board and made sure that all the computers in the labs had the drivers installed for it.  We had 2 installation failures: on one Windows laptop, my son was unable to get the serial ports to work and one Mac laptop couldn’t install gnuplot.

The problem with the gnuplot installation on that Mac was not solvable by the techniques in the comments for Installing gnuplot—a nightmare, because all the methods there assume that you can install the command-line tools “make” and “gcc”.  The Mac had 10.6.8 installed, but the student had never bothered to install the development tools and had lost the original CD-ROM with the Xcode tools on it.  The Apple Developer site does not provide the command-line tools for anything older than 10.7.3.  The only workaround we could find was to download the 4.1GByte complete Xcode suite for OS 10.6.8, which I was not willing to wait around for. (Other students with 10.6.8 had no trouble installing gnuplot, because they already had the command-line tools, though they’d never used them.)

I did not look at the problem on the Windows machine (the student had to leave for class before I became available), but I don’t know that I could have done anything—my son knows more about Windows than I do, so if he was stuck, I probably would have been also.

Next year I’m going to want to do an install session before the first lab.  (Or, if we go to 2 labs a week, as the first lab.)

On Wednesday, I’ll start with another “do now” question, though I’m not sure what it’ll be on, since I’ve not yet gotten to the material for this week’s lab: how a microphone works. I’ll do a tiny bit of gnuplot (just the “fit” command) and try to get through how a microphone works and an idealized i-vs-v plot for the FET output of the microphone.

Today’s class went much better than last Friday’s.

I took the advice one of the students gave me last we and started with a “do now” question.  (She had actually suggested an “exit ticket”, but I don’t have the time management skills to leave a block of time at the end of class.)  The question I asked was a design task that was easy if you knew what you were doing, but subtly harder than the standard sort of text-book question, because it was a design question, not an analysis question:

You have sensor whose resistance varies from 1kΩ to 4kΩ with the property it measures.  Design a circuit whose output voltage varies from 1v (at 1kΩ) to 2v (at 4kΩ).

I gave the students 10 minutes to work on this at the beginning of class.  A good question to prompt discussion (according to the peer instruction blogs and websites) should be answerable by 30–80% of the students.  More than that and the question was too easy to be useful, and less than that and the question is too hard for peer discussion to be worthwhile.  It turned out that no one had gotten it after 10 minutes (too hard to use as a peer instruction question), so we used it as the basis for a class discussion.

Almost everyone realized that the desired circuit was a voltage source and a voltage divider (not too surprising, since that’s the only circuit they’ve used so far).  The majority also realized that the variable resistor had to be on the lower leg, between the output and ground, and a couple of the students could articulate why.  I suggested the common heuristic of trying extreme values (0 and ∞) for the variable resistor, to see whether the output voltage would go up or down as the resistance changed.

The students were then able to set up the simultaneous equations to solve for the input voltage and the fixed resistance.  The hole in everyone’s thinking when working on the problem initially is that they had not considered the voltage of the source as a design parameter to solve for, though one student had asked about it. This was the blind spot I was expecting, so I was able to use it as a teachable moment.  After we had the equations set up using mainly student input, I gave the students another minute or two to solve them, and about half the class was able to solve them correctly in the time provided. (I suspect that everyone could have if given enough time, but I didn’t want to take any more time in class—those who didn’t solve it in class could practice their algebra at home if they needed to.)  One student had made an algebra or arithmetic mistake, and gotten a source voltage smaller than one of the desired output voltages.  This was also a good mistake to get, since we could use it to talk about sanity checks on results.

I think that the 20 or so minutes of class was well spent, as we uncovered several important misconceptions, and raised awareness of all unspecified variables as potential design parameters, reasoning using extreme values, and the usefulness of sanity checks.

After that, we spent some time discussing different temperature sensors.  From the students, I got thermistor, infrared thermometer, mercury thermometer+camera, and enzyme + other sensor (pH, conductivity, color, …). I added RTD, silicon band-gap, and thermocouple to the mix.  We talked a little about the advantages and disadvantages of each. At the end, I also threw in bimetallic strips and tilt switches for one-bit digitization of temperature.  I wonder how many students will look at the thermostats in their apartments and try to figure out what sensor they include.

For the remainder of the class, we talked about gnuplot commands, particularly the “plot” command.

After class, several of us went over to the lab, where my son met us and helped the students install the DataLoger, python, pyserial, the Arduino environment, and gnuplot.  While he was doing that, I borrowed an Uno R3 Arduino board and made sure that all the computers in the labs had the drivers installed for it.  We had 2 installation failures: on one Windows laptop, my son was unable to get the serial ports to work and one Mac laptop couldn’t install gnuplot.

The problem with the gnuplot installation on that Mac was not solvable by the techniques in the comments for Installing gnuplot—a nightmare, because all the methods there assume that you can install the command-line tools “make” and “gcc”.  The Mac had 10.6.8 installed, but the student had never bothered to install the development tools and had lost the original CD-ROM with the Xcode tools on it.  The Apple Developer site does not provide the command-line tools for anything older than 10.7.3.  The only workaround we could find was to download the 4.1GByte complete Xcode suite for OS 10.6.8, which I was not willing to wait around for. (Other students with 10.6.8 had no trouble installing gnuplot, because they already had the command-line tools, though they’d never used them.)

I did not look at the problem on the Windows machine (the student had to leave for class before I became available), but I don’t know that I could have done anything—my son knows more about Windows than I do, so if he was stuck, I probably would have been also.

Next year I’m going to want to do an install session before the first lab.  (Or, if we go to 2 labs a week, as the first lab.)

On Wednesday, I’ll start with another “do now” question, though I’m not sure what it’ll be on, since I’ve not yet gotten to the material for this week’s lab: how a microphone works. I’ll do a tiny bit of gnuplot (just the “fit” command) and try to get through how a microphone works and an idealized i-vs-v plot for the FET output of the microphone.

Solarbotics has been sharing electronics, kits, and BEAM Robotics with the Geek community for over 17 years. We're based in Canada and send packages around the world every day, with free shipping in North America for orders over $99. Designing an Arduino-based mobile solar-powered data logging cat collar? We can help!