Broadcast Engineer at BellMedia, Computer history buff, compulsive deprecated, disparate hardware hoarder, R/C, robots, arduino, RF, and everything in between.
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Interfacing An Old Engine Cowl Flaps Indicator To USB

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[Glen Akins] had a WW2-era aircraft engine cowl flap indicator lying around (as you do) and thought it would make a jolly fine USB-attached indicator. The model in question is a General Electric model 8DJ4PBV DC Selsyn, which was intended for four-engined aircraft. For those not familiar with the purpose [Glen] explains in his detailed writeup, that piston-engine aircraft of that era were air-cooled, and during conditions of maximum engine power — such as during take-off — flaps on the side of the engine cowling could be opened to admit additional cooling airflow. These indicator dials were connected to a sender unit on each of the flap actuators, providing the pilots an indication of the flaps’ positions.

The mode of operation in the DC power environment of WW2-era aircraft utilised the concept of variable magnetic field orientation. The sender is a potentiometer, sending a voltage down the wire between 24V and ground. The indicator unit has a pair of coils set at 120 degrees around a ring, with the coils wired in series, and the center tap connected to the sender signal. The other ends of each coil connect to the DC power bus so that as the signal voltage varies, the coils produce a varying magnetic field. Lower voltages bias the field towards the coil connected to 24V, and higher voltages the other way. A permanent magnet in the center is attached to the indicator dial, with a small spring to bias it to the center. A very simple but effective arrangement, giving analog feedback of the actual flap position.

To interface this thing to modern technology, a custom PCB was constructed leveraging the USB functionality of the PIC16F1459 microcontroller, that [Glen] was already familiar with. Four Microchip MCP31HV41-502 digital potentiometers were pressed into service directly driving the coils of the indicator units. That might seem like an odd if not viable way to drive such a thing, but [Glen] goes into some extensive theory and some modeling to determine which devices would have sufficient margin, which is worth a read for the unfamiliar. After bit-banging the SPI connection to the digipots (even though the PIC has hardware SPI) [Glen] goes on to describe how the USB endpoints work, finishing off with a .NET application to drive it all.

We’ve seen plenty of hacks bringing retro hardware back to life, connecting to modern computing. Here’s a project that goes the other way, building custom aircraft instrumentation from modern parts.

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tekvax
2 days ago
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Burlington, Ontario
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Scramblepad Teardown Reveals Complicated, Expensive Innards

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What’s a Scramblepad? It’s a type of number pad in which the numbers aren’t in fixed locations, and can only be seen from a narrow viewing angle. Every time the pad is activated, the buttons have different numbers. That way, a constant numerical code isn’t telegraphed by either button wear, or finger positions when punching it in. [Glen Akins] got his hands on one last year and figured out how to interface to it, and shared loads of nice photos and details about just how complicated this device was on the inside.

Just one of the many layers inside the Scramblepad.

Patented in 1982 and used for access control, a Scramblepad aimed to avoid the risk of someone inferring a code by watching a user punch it in, while also preventing information leakage via wear and tear on the keys themselves. They were designed to solve some specific issues, but as [Glen] points out, there are many good reasons they aren’t used today. Not only is their accessibility poor (they only worked at a certain height and viewing angle, and aren’t accessible to sight-impaired folks) but on top of that they are complex, expensive, and not vandal-proof.

[Glen]’s Scramblepad might be obsolete, but with its black build, sharp lines, and red LED 7-segment displays it has an undeniable style. It also includes an RFID reader, allowing it to act as a kind of two-factor access control.

On the inside, the reader is a hefty piece of hardware with multiple layers of PCBs and antennas. Despite all the electronics crammed into the Scramblepad, all by itself it doesn’t do much. A central controller is what actually controls door access, and the pad communicates to this board via an unencrypted, proprietary protocol. [Glen] went through the work of decoding this, and designed a simplified board that he plans to use for his own door access controller.

In the meantime, it’s a great peek inside a neat piece of hardware. You can see [Glen]’s Scramblepad in action in the short video embedded below.

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tekvax
8 days ago
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Burlington, Ontario
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Hey, it's the WKRP turkey drop!

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I am thankful that my dogs are so well-behaved. I am thankful my parents survived the pandemic and my mother's cancer treatment. I am thankful for my daughter, who sleeps all day. I am thankful for my neighbors, who care for each other and our neighborhood. — Read the rest

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tekvax
8 days ago
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Burlington, Ontario
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Generating Two-Factor Authentication Codes With a Commodore 64

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A Commodore SX-64 showing a six-digit code and a countdown timer

If you’ve used a corporate VPN or an online-banking system in the past fifteen years or so, chances are you’ve got a few of those little authenticator key fobs lying around, still displaying a new code every 30 seconds. Today such one-time codes are typically sent to you by text message or generated by a dedicated smartphone app, which is convenient but a bit boring. If you miss having a dedicated piece of hardware for your login codes, then we’ve got good news for you: [Cameron Kaiser] has managed to turn a Commodore SX-64 into a two-factor authenticator. Unlike a key fob that’s one gadget you’re not likely to lose, and any thief would probably need to spend quite some time figuring out how to operate it.

The SX-64, if you’re not familiar, is the portable version of the venerable Commodore 64. Weighing in at more than 10 kg it’s not quite a MacBook Air, but it does come with a built-in color monitor and 5.25″ floppy drive. The CPU is an 8-bit 6510 running at about 1 MHz, and as you might imagine it was not a trivial task to implement cryptographic routines on it. Working directly from the definitions in RFC 6238, [Cameron] first determined all the necessary bits: an SHA-1 hasher, an HMAC generator and several routines to manipulate dates and times.

The SHA-1 algorithm and HMAC functions might seem complex, but in the end they boil down to performing addition, subtraction and several bitwise logical functions on 32-bit numbers. Lots of steps if you can only work with eight bits at a time, but nothing that even a 6510 can’t do in a reasonable amount of time, especially when running carefully hand-crafted assembly code.

Working with dates and times turned out to be more complicated. The few real-time clock add-ons that were available for the Commodore 64 series all return the time directly in human-readable format: great for everyday use but not so great for calculations that require Unix time. Converting between the two involves lots of multiplication and division, which takes forever if you don’t have a hardware multiplier. [Cameron]’s blog post is full of detail on how to optimize calculations on constrained hardware, and is an interesting read even if you’re working with modern processors.

The end result of the exercise looks almost exactly like a typical authentication app on your smartphone, including that annoying countdown bar. If you’re looking for a slightly more compact solution, you can do the same thing on an ESP32. Need a refresher on two-factor authentication techniques? We’ve got you covered.

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tekvax
16 days ago
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Burlington, Ontario
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The smallest CP/M microcomputer ever #CPM #VintageComputing #RaspberryPi @Hascksterio @Raspberry_Pi

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Designed with a minuscule footprint, this fully-functional CP/M computer build uses just two main components: a Tiny 2040 and an Adafruit microSD reader.

Software engineer and vintage computing enthusiast Kian Ryan writes:

“I’ve been using the RC2014 as a a CP/M development machine, especially while developing a cross-platform Rogue-like game. I love it,” Ryan explains, referring to the popular modular Zilog Z80 computer kit. “And whilst it’s a hell of a lot more portable than carrying a Osborne 1 or a Amstrad CPC 6128, it’s not something I can keep in the laptop bag and just pull out at the coffee shop (Both the RC2014 Mini with CP/M upgrade and the Extreme Kits RC2040 are ideally suited for this). I wanted to see if I could put together a truly tiny CP/M based system using RunCPM and the RunCPM-Pi-Pico project and make it even smaller.”

You can see more on hackster.io and on this blog and GitHub.

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tekvax
16 days ago
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Burlington, Ontario
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Detecting Radiation for Fun and Profit

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It used to be that every well-stocked doomsday bunker had a Geiger counter. These days, you don’t have to have a big tube-based meter. You can inexpensively get a compact digital instrument to handle your radiation detection needs. [DiodeGoneWild] reviews and tears down such a unit from FNIRSI. The case looks like several other similar instruments we’ve seen lately, so presumably, someone is mass-producing these handheld meter cases. You can see the video, below. The meter reads the absolute radioactivity and can also measure cumulative exposure.

After measuring a few common radioactive items, we get to the teardown. Inside, of course, is an ordinary tube. A few screws reveal a typical rechargeable battery, a fairly simple PCB with a microcontroller and battery backup for the real-time clock. A lot of the board is involved in multiplying voltage up to the several hundred volts required for the Geiger tube.

The other side of the PCB has only buttons, a vibration motor, and, of course, the LCD. We don’t know how you might test the relative accuracy other than comparing it to a known-good meter. The bare tube was, of course, more sensitive without the plastic cover, but that could be calibrated out, too.

A Geiger counter doesn’t have to have a lot of parts. Either way, a surprising number of things will set them off.

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tekvax
16 days ago
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Burlington, Ontario
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