Pi Pico Enhances RadioShack Computer Kit

While most of us now remember Radio Shack as a store that tried to force us to buy batteries and cell phones whenever we went to buy a few transistors and other circuit components, for a time it was an innovative and valuable store for electronics enthusiasts before it began its long demise. Among other electronics and radio parts and kits there were even a few DIY microcomputers, and even though it’s a bit of an antique now a Raspberry Pi Pico is just the thing to modernize this Radio Shack vintage microcomputer kit from the mid 80s.

The microcomputer kit itself is built around the 4-bit Texas Instruments TMS1100, one of the first mass-produced microcontrollers. The kit makes the processor’s functionality more readily available to the user, with a keypad and various switches for programming and a number of status LEDs to monitor its state. The Pi Pico comes into the equation programmed to act as a digital clock with an LED display to drive the antique computer. The Pi then sends a switching pulse through a relay to the microcomputer, which is programmed as a binary counter.

While the microcomputer isn’t going to win any speed or processing power anytime soon, especially with its clock signal coming from a slow relay module, the computer itself is still fulfilling its purpose as an educational tool despite being nearly four decades old. With the slow clock speeds it’s much more intuitive how the computer is stepping through its tasks, and the modern Pi Pico helps it with its tasks quite well. Relays on their own can be a substitute for the entire microcontroller as well, like this computer which has a satisfying mechanical noise when it’s running a program.

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A 1960s PLC Gives Up Its Secrets

When it comes to process automation, the go-to part in most industrial settings is a Programmable Logic Controller, or PLC. These specialized computers will have a modern microcontroller running the show, but surprisingly the way they are programmed still has echoes of a time before electronic PLCs when such control would have been electromechanical.

[Thomas Scherrer] has an interesting design to tear down, it’s a Siemens electromechanical motor controller from the early 1960s. It’s not quite the huge banks of relays which would have made a fully-blown PLC back in those times, but it’s a half-way house with some simple programming capability in the form of several channels of adjustable time delay.

We’re partly sad to see this unit being subjected to a destructive teardown, but nevertheless it’s interesting to see all those very period components. The current sensor has a mechanism similar to a moving coil meter, and the four-channel timer is a mechanical sequencer with four adjustable cam-driven switches. We’re not sure we would be cracking open selenium rectifiers with such nonchalance though.

These units were built to a very high quality indeed, and though it’s obvious this one comes from a decommissioned installation it’s not beyond possibility to think there might be some of them still doing their job over six decades after manufacture. Have any of you seen one of these or something like it in operation recently? Let us know in the comments. Meanwhile the video is below the break.

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Simple Magnetic Levitator

[Stoppi] always has exciting projects and, as you can see in the video below, the latest one is a very simple magnetic levitator design. The design is classic and simple: a 5 V regulator IC, a Hall effect sensor, a 741 op amp, and a MOSFET to turn the electromagnet on and off.

Sure, there are a few passive components and a diode, too, but nothing exotic. The sensor normally presents 2.5 V of output. The voltage rises or drops depending on the polarity of the magnetic field. The stronger the field, the more the voltage changes away from the 2.5 V center.

The op amp acts as a comparator with a potentiometer setting the trip point. As the ball moves up towards the coil, the voltage increases, triggering the comparator, which turns off the FET. With no current through the coil, there’s no more electromagnet, and the ball starts to fall.

Of course, as the ball falls, the voltage from the sensor also drops, and this eventually turns on the electromagnet. The ball eventually reaches a relatively stable position.

This is one of those cases where a simple analog circuit might work better than a digital one. Or make it hard on yourself and use an FPGA.

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Arctic Adventures With A Data General Nova II — The Equipment

As I walked into the huge high bay that was to be my part-time office for the next couple of years, I was greeted by all manner of abandoned equipment haphazardly scattered around the room. As I later learned, this place was a graveyard for old research projects, cast aside to be later gutted for parts or forgotten entirely. This was my first day on the job as a co-op student at the Georgia Tech Engineering Experiment Station (EES, since renamed to GTRI). The engineer who gave me the orientation tour that day pointed to a dusty electronic rack in one corner of the room. Steve said my job would be to bring that old minicomputer back to life. Once running, I would operate it as directed by the radar researchers and scientists in our group. Thus began a journey that resulted in an Arctic adventure two years later.

The Equipment

The computer in question was a Data General (DG) mini computer. DG was founded by former Digital Equipment Corporation (DEC) employees in the 1960s. They introduced the 16-bit Nova computer in 1969 to compete with DEC’s PDP-8. I was gawking at a fully-equipped Nova 2 system which had been introduced in 1975. This machine and its accessories occupied two full racks, with an adjacent printer and a table with a terminal and pen plotter. There was little to no documentation. Just to turn it on, I had to pester engineers until I found one who could teach me the necessary front-panel switch incantation to boot it up. Continue reading “Arctic Adventures With A Data General Nova II — The Equipment”

Lorenz Attractor Analog Computer With Octave Simulation

[Janis Alnis] wanted to build an analog computer circuit and bought some multiplier chips. The first attempt used apparently fake chips that were prone to overheating. He was able to get it to work and also walked through some Octave (a system similar to Matlab) simulations for the circuit. You can follow along in the video below.

Getting the little multiplier chips into the breadboard was a bit of a challenge. Of course, there are a variety of ways to solve that problem. The circuit in question is from the always interesting [Glen’s Stuff] website.

From that site:

The Lorenz system, originally discovered by American mathematician and meteorologist, Edward Norton Lorenz, is a system that exhibits continuous-time chaos and is described by three coupled, ordinary differential equations.

So, the circuit is an analog solution to the system of differential equations. Not bad for a handful of chips and some discrete components on a breadboard. We’ve seen a similar circuit on Hackaday.io.

Check out our recent competition winners if you want to see op amps do their thing. Analog computers were a thing. They aren’t always that complicated, either.

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Random Number Generation By Brain

If you want to start an argument in certain circles, claim to have a random number generation algorithm. Turns out that producing real random numbers is hard, which is why people often turn to strange methods and still, sometimes, don’t get it right. [Hillel Wayne] wanted to get a “good enough” method that could be done without a computer and found the answer in an old Usenet post from random number guru [George Marsaglia].

The algorithm is simple. Pick a two-digit number — ahem — at random. OK, so you still have to pick a starting number. To get the next number, take the top digit, add six, and then multiply by the bottom digit. So in C:  n1=(n/10+6)*(n%10). Then use the last digit as your random number from 0 to 9. Why does it work? To answer that, the post shows some Raku code to investigate the behavior.

In particular, where does the magic number 6 come into play? The computer program notes that not any number works well there. For example, if you used 4 instead of 6 and then started with 13, all your random digits would be 3. Not really all that random! However, 6 is just a handy number. If you don’t mind a little extra math, there are better choices, like 50.

If you think humans are good at picking random numbers, ask someone to pick a number between 1 and 4 and press them to do it quickly. Nearly always (nearly) they will pick 2. However, don’t be surprised when some people pick 141. Not everyone does well under pressure.

If you want super random numbers, try a lava lamp. Or grab some 555s and a few Nixie tubes.

A Dim Bulb Tester Is For Testing Other Equipment, Not Bulbs

If you’re testing old stereo equipment, a dim bulb tester can really come in handy. It’s not for testing bulbs, though, it’s a tester that uses a dim bulb to test other things. [Nicholas Morganti] explains it all in his guide to making your own example of such a tool. Just be wary — you need to know what you’re doing with mains voltages to do this safely!

The dim bulb is a deceptively simple tool that nonetheless often proves useful in diagnostics. It normally just consists of a bulb connected in series with the equipment under test. The bulb is intended to be a similar wattage to the power draw of the equipment itself. Take for example, an amplifier. If the bulb glows brightly when the amp is under no load, it suggests there may be a short circuit somewhere. That’s because the glowing bulb indicates that plenty of current is being drawn under a condition when very little should be flowing. The bulb protects the equipment by essentially acting as a bit of a current limiting device. It’s a soft-start tool for a piece of vulnerable equipment.

Building one is usually as simple as gathering an enclosure, a plug receptacle, a bulb socket, and some other ancillary parts to lace everything together. [Nicholas] explains it all with clear diagrams and tells you how to follow along. It’s easy enough, but you really need to know what you’re doing to use one safely, as mains voltages are involved.

It’s a great tool to have if you’re getting into amplifier repair or similar work on old gear. If you’ve been whipping up your own must-have tools, don’t hesitate to let us know!