HP1973 Project Highlights Workings Of HP-45 Calculator

July 24, 2023 by Chris Lott 3 Comments

[Sarah K Marr] dabbles in retrocomputing and has a fascination with the Hewlett Packard HP-45 calculator, the second calculator in HP’s series introduced in 1973. Over a year ago, she wrote an HP-45 emulator for use on a terminal, dubbed HP45TERM. Not content with success, she upped the challenge and decided to build an even better emulator with a full-featured GUI written in Python. Oh, and she made it multi-platform as well. The result is the HP1973 project.

[Sarah] thought it would take just a few days, but it grew into a much bigger project, as often happens. We’re glad it did because the results are fantastic. The emulator gives you access not only to the calculator itself but can see everything under the hood. The emulator provides full ROM visibility, hardware registers, and standard debugging operations like single stepping. ROM images are available for the HP-45, the HP-35, and the HP-80. The GUI display is configurable, and there’s a plethora of help and information explaining the calculator’s internals. Pre-built binaries are available for MacOS, Windows, and Python source code (3.10.10+) for all operating systems (you’ll need to `pip install numpy` first). The emulation is faithful to the original calculator, and even the hidden timer function can be accessed.

Check this out if you’re into retro calculators. Our own Al Williams wrote about the history of the HP-35 back in 2018 if you want to learn more. Thanks to [J Peterson] for sending in the tip.

Amateur Estimates Of Venusian Day Using Arecibo Data

July 23, 2023 by Chris Lott 7 Comments

[Nathaniel Fairfield] aka [thandal] was curious about the actual rotation and axis tilt of Venus. He decided to spin up at GitHub Python repository to study the issue further, as one does. The scientific literature shows a wide range of estimates and variations for the planet’s rotation and axis tilt. He wondered if the real answer might be found in a publicly available set of uncalibrated delay-doppler images of Venus. These data were collected by the former Arecibo Observatory in Puerto Rico from 1988 through 2020. [Thanda] observed that the planet’s rotation appears to be speeding up slightly, and furthermore, his estimates of the orbital axis were within 0.01 degrees of the International Astronomical Union’s (IAU) values. [Note: Venus is a bit confusing — one planetary rotation, 243 Earth days, is longer than its year, 225 Earth days].

Estimations of Venusian Orbital Period, [Thandal] Estimates in Green

Aligning and calibrating the raw data was no trivial task. You have to consider the radar’s (Earth’s) position and time, as well as Venus. Complicating the math even more, some times the radar was operated in a bistatic mode, with the Green Bank Telescope in West Virginia being the receiver.

There’s a lot of interesting signal processing going on here. The Doppler-delay data consists of images that are 8091×8092 array of complex values, has to be mapped onto the Venus geoid. Then by using various surface features, one can compare their positions vs time and obtain an estimate of rotational speed and tilt. If these kinds of calculations interest you, be sure to check out [Thandal]’s summary report, and also take note of the poliastro Python astrodynamics library. Why is this important? One reason to better plan future missions.

South Korea Successfully Sends Satellites To Orbit

May 30, 2023 by Chris Lott 8 Comments

South Korea’s KARI ( Korea Aerospace Research Institute ) successfully put a commercial satellite into orbit Thursday, achieving another milestone in their domestic space program. The Nuri rocket (aka KLSV-2) left the Naro Space Center launch pad on the southern coast of the peninsula at 18:24 KST, after a communications glitch in the pad’s helium tank facility caused a one-day slip. The primary payload was the 180 kg refrigerator-sized Earth observation satellite NEXTSat-2. It uses synthetic aperture radar (SAR) and also has instruments to observe neutrons in near-Earth orbit due to the impact of solar activity on cosmic radiation. In addition, seven CubeSats were successfully deployed:

Justek JLC-101-V1.2, to verify satellite orbital control system
Lumir, measuring cosmic radiation and testing rad-hardened microprocessor design
Cairo Space, weather observation and space debris technology demonstration
KASI-SAT (Korea Astronomy and Space Science Institute) SNIPE, actually four nano-sats which will achieve a 500 km – 600 km polar orbit and fly in formation to measure plasma variations.

It seems that SNIPE-C, Justek, and Lumir are having communication troubles and may be lost. Ground controllers are still searching. This launch comes almost one year after the previous launch of a dummy satellite in June, which we wrote about last year.

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Supercon 2022: Nick Poole Makes A Jolly Wrencher Tube

May 23, 2023 by Chris Lott 5 Comments

[Nick Poole] shared his circuitous journey into the obscure world of homemade vacuum tubes on the Supercon 2022 stage. It began innocently enough when he saw [Usagi Electric]’s single bit computer vacuum tube computer, which uses dozens of vacuum tubes. He got to wondering, could you make vacuum-tube-like devices containing multiple elements? There are some examples, like the 256-bit memory Selectron tube from the 1950’s, but nothing general purpose like a 555 timer or quad NAND gate packages. Unencumbered by a deep understanding of how vacuum tubes work, [Nick] proceeds to fill this void by imagining Integrated Thermionic, a fictitious company that exists in an alternate history where transistors were not invented and the vacuum tube reigns supreme. He also showcases a variety of innovative products that Integrated Thermionics manufactured over the decades, including surface mount tubes.

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North Korean Karaoke Machine Teardown

May 19, 2023 by Chris Lott 9 Comments

Karaoke is a very popular pastime in Seoul — there are venues where you can sing on a stage, sing in rooms with your friends, and even sing solo in coin-operated karaoke booths on the bullet train. Apparently it is also popular in North Korea as well — [Martyn Williams] of the North Korea Tech blog reported on an interesting teardown by web hacker [Will Scott]. It is the Tianchi v700 machine, a Chinese product tailored for North Korean users, obtained online back in 2020.

Unlike the karaoke machines encountered by this author in South Korea, the v700 form factor is a 19.5-inch Android tablet with touch-screen and all the necessary interfaces you’d expect: external video, speakers, and microphone, as well as WiFi and Ethernet for content upgrade and online payment systems. Not surprisingly, the connectivity aspects of the machine are not used in the North Korean model, but with a large catalog of pre-loaded music, it’s perfectly usable as a stand-alone device.

[Will] dug into the innards of the machine and discovered it was powered by an Allwinner ARM processor (seemingly the H6 V200, a quad-core ARM Cortex-A53). He also found it uses a swappable external disk to hold the songs, but all the files were encrypted. You can read more details in the blog post linked above, but eventually he was successful in decoding the disk and accessing the material.

The V700 consults both “/proc/cpuinfo” to learn the CPU serial number of the device it is on, and a binary file associated with the device file system structure as part of its method for determining its AES (Advanced Encryption Standard) key. It then ignores all of these device-specific items, and reverts back to a static key “87654321” stored in the binary.

All the songs on the disk were posted up on the Internet Archive. Check them out if you’re curious what North Korean karaoke songs sound and look like. One video that caught our attention was about CNC machines (see the video linked below the break). [Martyn] has been covering technology issues related to North Korea since 2011. In 2016, he learned after the fact that his website had been banned by the South Korean authorities. Believing this was in error, he appealed the ban and eventually prevailed in the courts. We wrote about some of [Will]’s research on consumer computing technology back in 2017 if you’re interested in learning more.

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The $50 Pen Plotter

March 19, 2023 by Chris Lott 23 Comments

[Arca] sets out to build himself a low-cost pen plotter that doesn’t require access to a 3D printer. The plotter uses a coreXY arrangement, powered by 28BYJ-48 stepper motors, which he overdrives with +12 VDC to increase the torque. Pen up and down control is done using a stepper motor salvaged from a DVD reader. The frame is constructed using PVC electrical conduit and associated fittings, and [Arca] uses the hot glue gun quite liberally. Steppers were driven by A4988 modules with heatsinks, and motion control is provided by GRBL running on an Arduino UNO.

He has a few issues with glitches on the limit switches, and is continuing to tweak the design. There is no documentation yet, but you can discern the construction easily from the video if you want to try your hand at making one of these. This is a really cool DIY plotter, and many parts you probably have laying around your parts boxes. As [Arca] says, it’s not an AxiDraw, but the results are respectable. Keep a lookout for part 2 of this project on his YouTube channel.

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Meet The New Moteus BLDC Controller Board, The N1

March 18, 2023 by Chris Lott 4 Comments

[Josh] over at mjbots just released a new version of the moteus controller board, dubbed the moteus-n1. One change is that the volume and footprint size has been reduced. Considering many people, [Josh] included, use these controllers to operate robotic dogs, smaller is better. The previous moteus controller maxed out at 44 V, but the n1 can run at up to 54 V, allowing use of 48 V power supplies. And [Josh] improved the interface circuitry, making it much more flexible than before. This comes at an increased price, but he sells both versions — parts availability permitting. And like the previous versions of the moteus controller, this is an open source project and you’re free to build it yourself. You can check out the complete design package at the project’s GitHub repository.

One helpful point is that the firmware for the n1 is the same, it simply enables new features related to the I/O ports. This means a user could swap in a new controller with no impact to their system. Maintaining firmware compatibility was just one of the challenges [Josh] faced along the way. Squeezing additional functionality into the small number of user-exposed I/O pins was a chore, but dealing with supply chain issues was a big headache:

…make a revision that leveraged the parts I had, along with ensuring that the parts I needed were achievable to purchase in a reasonable time frame. Some parts orders for this batch were placed nearly a year ago.

Check out moteus if you need a brushless servo controller. We covered the previous major upgrade last year, which was primarily firmware and interface focused.