Restoring a Dried-Out Securit Liquid Chalk Marker

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Most Securit liquid chalk markers can be revived, as they feature water-based pigment ink and a valve-action system with a removable nib. The restoration steps: If the nib is frayed or permanently misshapen, Securit sells replacement nib sets, allowing you to keep using the marker as long as ink remains in the reservoir.

An Interesting Two-Transistor Relay Timer

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I came across the printed circuit board for this circuit completely by accident. It looked like an interesting and clever little design, and I had more than enough suitable parts lying around in my component drawers, including a pile of spare relays. So I decided to build one and measure what it could actually do. … Read more

On the Teardown Bench: Radtel RT-470 – What’s Inside a Modern Handheld Radio?

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This time, the device on the teardown bench is not broken. My Radtel RT-470 is fully functional and gets regular use; it simply needed a thorough cleaning. For that reason, I did not take it apart any further than what you can see in the photographs. Even so, there is plenty to discover about how … Read more

How to eliminate duplicate photos from LrC

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There are many reasons why duplicates appear in your catalogs but even if you are careful while you import photos, encountering duplicates is inevitable. Here is how to use the plug-in Teekesselchen to find duplicates of photos. This is a fast duplicate finder plug-in for Adobe Lightroom using EXIF meta-data. It requires Lightroom 3.x, 4.x, … Read more

The Honeywell XC100D on the Dissection Table

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A Honeywell XC100D carbon monoxide alarm that had reached the end of its service life recently came into my possession. At this stage, the unit may still appear to operate normally, but it can no longer be considered fully reliable. It signals this condition with a sharp chirp once every minute, accompanied by a flash … Read more

“15 kV” High-Voltage Generator

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The module shown in the picture can be purchased online for around 2–3 euros. It is a small “15 kV” generator suitable, for example, for secondary-school science experiments or for use as a negative ion generator/air ionizer. The circuit can produce a stable, high-temperature, high-frequency arc, which can easily ignite small combustible materials, such as … Read more

How to Tame Bulk LaTeX Equations

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Generative AI—like Gemini—has become an essential daily tool for researchers, engineers, and academics. However, its use comes with a recurring professional pain point: handling mathematical and technical formulas. If you ask the AI to derive a calculation or specify a physical range, the output will almost certainly arrive in raw LaTeX format (for example: $550 … Read more