New Study Tells Us Where To Hide When The Nukes Are Coming

January 19, 2023 by Lewin Day 70 Comments

Geopolitics is a funny thing. Decades can go by with little concern, only for old grudges to suddenly boil to the surface and get the sabers a-rattlin’. When those sabers happen to be nuclear weapons, it can be enough to have you mulling the value of a bomb shelter in your own backyard.

Yes, every time the world takes a turn for the worse, we start contemplating what we’d do in the event of a nuclear attack. It’s already common knowledge that stout reinforced concrete buildings offer more protection than other flimsier structures. However, a new study has used computer modelling to highlight the best places to hide within such a building to maximise your chances of survival.

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Addressable LEDs From A Z80

January 19, 2023 by Jenny List 3 Comments

If you buy WS2812s under the Adafruit NeoPixel brand, you’ll receive the advice that “An 8 MHz processor” is required to drive them. “Challenge Accepted!“, says [ShielaDixon], and proceeded to first drive a set from the 7.3 MHz Z80 in an RC2014 retrocomputer, and then repeat the feat from a 3.5 MHz Sinclair ZX Spectrum.

The demos in the videos below the break are all programmed in BASIC, but she quickly reveals that they call a Z80 assembler library which does all the heavy lifting. There’s no microcontroller behind the scenes, save for some glue logic for address decoding, the Z80 is doing all the work. They’re all implemented on a pair of RC2014 extension cards, a bus that has become something of a standard for this type of retrocomputer project.

So the ubiquitous LEDs can be addressed from some surprisingly low-powered silicon, showing that while it might be long in the tooth the Z80 can still do things alongside the new kids. For those of us who had the Sinclair machines back in the day it’s particularly pleasing to see boundaries still being pushed at, as for example in when a Z80 was (almost) persuaded to have a protected mode.

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LED Driver Circuit For Safety Hat Sucks Single AAA Cell Dry

January 19, 2023 by Donald Papp 21 Comments

[Petteri Aimonen] created an omnidirectional LED safety light to cling to his child’s winter hat in an effort to increase visibility during the dark winter months, but the design is also great example of how to use the Microchip MCP1640 — a regulated DC-DC step-up power supply that can run the LEDs off a single AAA cell. The chip also provides a few neat tricks, like single-button on/off functionality that fully disconnects the load, consuming only 1 µA in standby.

[Petteri]’s design delivers 3 mA to each of eight surface-mount LEDs (which he says is actually a bit too bright) for a total of about 20 hours from one alkaline AAA cell. The single-layer PCB is encased in a clear acrylic and polycarbonate enclosure to resist moisture. A transistor and a few passives allow a SPST switch to act as an on/off switch: a short press turns the unit on, and a long press of about a second turns it back off.

One side effect is that the “off” functionality will no longer work once the AAA cell drained too badly, but [Petteri] optimistically points out that this could be considered a feature: when the unit can no longer be turned off, it’s time to replace the battery!

The usual way to suck a battery dry is to use a Joule Thief, and while this design also lights LEDs, it offers more features and could be adapted for other uses easily. Interested? [Petteri] offers the schematic, KiCAD file for the PCB, and SVG drawing of the enclosure for download near the bottom of the project page.