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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Upgrading At Least One Component Of A TI Calculator

Even though Texas Instruments were the first company to produce an integrated circuit and a microprocessor, their success as a company in the 60s and 70s was not guaranteed. At the time there wasn’t much demand for previously non-existent products like these, so to drive some business they built the first hand-held calculator, a venture that they are still famous for today. Since then, though, they’ve become a bit of a punchline for producing calculators with decades-old technology but with modern price tags, so while this business model was quite successful if you want a calculator with a few modern features you’ll have to take a DIY approach like this calculator retrofitted with a LiPo battery.

The modern battery pack, with a lithium polymer battery at its core, includes all of the circuitry needed to integrate it seamlessly into the TI-59 calculator, which is all available on the project’s GitHub page. This calculator originally used a 9V battery, so the new battery pack includes a boost converter to match the 3.7V from the new battery to the needs of the old calculator. It doesn’t stop there, though. The pack is rechargeable from an included USB-C port, has a built-in charge controller, and is housed in its own custom-built case that fits neatly into the calculator where the old battery would sit.

While this wouldn’t be a drop-in replacement for more modern calculators like the TI-83/84 and TI-89, a new case and a different boost converter would solve the problem of the AAA batteries dying during exams. It might make the calculators non-compliant with various standardized testing requirements, though (which TI was also instrumental in developing) so you may want to verify with your testing standard of choice before modifying a calculator you need for an exam. But if all the rules are off, why not add Wi-Fi to it too?

TMS 1000 Microcontroller - By Antonio Martí Campoy - Own work, CC BY-SA 4.0

The Early History Of The Microcontroller: It Came From Texas

Ti’s presentation of the rapid integration of calculator chips.
Ti’s presentation of the rapid integration of calculator chips.

Although for most generations alive today the era of microcontrollers (MCU) feels like it starts somewhere with the Intel 8051 and AVR MCUs, the history of these self-contained computing marvels that are now found just about anywhere begins long before those were even conceptualized. In a recent article titled Tiny Computers From Texas, [Babbage] goes through this early history of what would ultimately become such an integral part of daily life.

An MCU is defined as a small, self-contained computer, which requires few to no external components to function. This contrasted with the more traditional MPUs, or microprocessor units, where a computer was assembled out of one or more MPUs, I/O chips, memory SRAM and so on. It’s perhaps little surprise that the drive towards MCUs was the result of primarily the calculator market, where competing firms were trying to upstage each other with higher levels of integration into as few chips as possible, while driving down costs and power usage.

Ultimately, the Texas Instruments TMS 1000 was the first true MCU that got produced in large volumes after its release in 1974. Moving beyond calculators, the TMS 1000 found its way into toys, including the Speak & Spell – which uses another Ti chip (TMS 5100) for the voice synthesis – so that today any toy can be interactive in exciting and often noisy ways.

Back in 2020 we took our own affectionate look at this chip.

Showing pulse oximeter and color sensor combining to measure oxygen in blood and skin tone

Perfecting The Pulse Oximeter

We’re always looking for interesting biohacks here on Hackaday, and this new research article describing a calibrated pulse oximeter for different skin tones really caught our attention.

Pulse oximeters are handy little instruments that measure your blood oxygen saturation using photoplethysmography (PPG) and are a topic we’re no strangers to here at Hackaday. Given PPG is an optical technique, it stands to reason that its accuracy could be significantly affected by skin tone and that has been a major topic of discussion recently in the medical field. Given the noted issues with pulse oximeter accuracy, these researchers endeavored to create a better pulse oximeter by quantifying skin pigmentation and using that data to offset errors in the pulse oximeter measurements. A slick idea, but we think their results leave a lot to be desired.

Diagram showing pulse oximeter and color sensor combining to measure oxygen in blood and skin toneTheir idea sounds pretty straightforward enough. They created their own hardware to measure blood oxygen saturation, a smartwatch that includes red and infrared (IR) light-emitting diodes (LED) to illuminate the tissue just below the surface of the skin, and a photosensor for measuring the amount of light that reflects off the skin. But in addition to the standard pulse oximeter hardware, they also include a TCS34725 color sensor to quantify the user’s skin tone.

So what’s the issue? Well, the researchers mentioned calibrating their color sensor to a standard commercially-available dermatology instrument just to make sure their skin pigmentation values match a gold standard, but we can’t find that data, making it a bit hard to evaluate how accurate their color sensor actually is. That’s pretty crucial to their entire premise. And ultimately, their corrected blood oxygen values don’t really seem terribly promising either. For one individual, they reduced their error from 5.44% to 0.82% which seems great! But for another user, their error actually increases from 0.99% to 6.41%. Not so great. Is the problem in their color sensor calibration? Could be.

We know from personal experience that pulse oximeters are hard, so we applaud their efforts in tackling a major problem. Maybe the Hackaday community could help them out?

A small green circuit board with a tiny OLED display

An Oscilloscope Trigger For Vintage Video Processors

Working on retro computers is rarely straightforward, as [ukmaker] recently found out while designing a new display interface. Their oscilloscope was having trouble triggering on the video signal produced by older video circuitry, so they created the Video Trigger for Retrocomputers.

The Texas Instruments TMS9918 video display controller was used across a range of 1980s game consoles and home computers, from the well-known ColecoVision to Texas Instruments’ own TI-99/4. Substantial retro computing heritage notwithstanding, the video output from this chip was (for reasons unknown) not quite compatible with the Hantek DSO1502P oscilloscope. And without a better understanding of the video signal, it was difficult to use the chip with newer TFT displays, being designed for CRT televisions with more forgiving NTSC tolerances.

Maybe a different scope would have solved the problem, but [ukmaker] had a feeling that the ‘scope needed an external trigger signal. The Video Trigger project uses a LM1881 sync separator to tease out the horizontal and vertical sync signals from the vintage video chip, with the output piped into an ATmega 328P. Along with a smattering of discrete components, the ATmega aids the user in selecting which line to frame a trigger on, and the slope of the horizontal sync signal to align to. A tiny OLED display makes configuration easy.

If this has piqued your interest, [ukmaker] also has a great write-up over on GitHub with all the gory details. Maybe it will help you in your next vintage computing caper. Having the right tool can make all the difference, like this homebrew logic meter for hobby electronics troubleshooting. Or if you want to know more about the mystical properties of analog NTSC video, we’ve covered that, too.

Exploring Texas Instrument’s Forgotten CPU

Texas Instruments isn’t the name you usually hear associated with the first microprocessor. But the TI TMX 1795 was an 8008 chip produced months before the 8008. It was never available commercially, though, so it has been largely forgotten by most people. But not [Ken Shirriff]. You can see a demo from 2015 of the device in the video below, too.

The reason the chips have the same architecture is they were built to replace the same large circuit board inside a Datapoint 2200 programmable terminal. These were big beasts that could be programmed in BASIC or PL/B.

Datapoint asked Intel to shrink the board to a chip due to heating problems — but after delays, they instead replaced the power supply and lost interest in the device. TI heard about the affair and wanted in on the deal. However, Datapoint was unimpressed. The chip didn’t tolerate voltage fluctuations very well, since they had replaced the power supply and had a new CPU design that was faster than the chip would be. They were also unimpressed with how much stuff you had to add to get a complete system.

So why did the Intel 8008 work out in the marketplace but the TI chip didn’t? After all, Datapoint decided not to use the 8008, also. But as [Ken] points out, the 8008 was much smaller than the TI chip and, thus, was more cost-effective to produce.

As usual, [Ken]’s posts are always interesting and enlightening. He’s looked at a lot of old computers. He’s even dug into old space hardware. Great stuff!

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Talking To A Texas Instruments Calculator

Texas Instruments is a world-class semiconductors company, but unfortunately what they are best known for among the general public is dated consumer-grade calculators thanks to entrenched standardized testing. These testing standards are so entrenched, in fact, that TI has not had to update the hardware in these calculators since the early 90s. They still run their code on a Z80 microcontroller, but [Ben Heck] found himself in possession of one which has a modern ARM coprocessor in it and thus can run Python.

While he’s not sure exactly what implementation of Python the calculator is running, he did tear it apart to try and figure out as much as he could about what this machine is doing. The immediately noticeable difference is the ARM coprocessor that is not present in other graphing calculators. After some investigation of test points, [Ben] found that the Z80 and ARM chips are communicating with each other over twin serial lines using a very “janky” interface. Jankiness aside, eventually [Ben] was able to wire up a port to the side of the calculator which lets him use his computer to send Python commands to the device when it is in its Python programming mode.

While there are probably limited use cases for 1980s calculators to run Python programs, we can at least commend TI for attempting to modernize within its self-built standardized testing prison. Perhaps this is the starting point for someone else to figure out something more useful to put these machines to work with beyond the classroom too. We’ve already seen some TI-84s that have been modified to connect to the Internet, for example.

Thanks to [Nikša] for the tip!

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