Barnaby Walters

Arranging atoms and pressurising air in a variety of manners, such as:

Pronouns: he/him/his

  1. It appears that the popular Riden/Ruideng/RD Tech DP/DPS/DPH series power supplies use low-side current sensing, which can lead to some unexpected (and potentially destructive) behaviour in a situation where you have multiple unisolated power rails.

    For example, I put together a little box with a DP30V5A providing a variable, current-limited rail, and three LM2595 modules providing fixed 12v, 5v and 3.3v rails. As none of these supplies are isolated, and can therefore not be used to provide negative rails, I tied all their 0V outputs together. This led to the DP30V5A reporting a completely false current consumption of about 33% of the measured value.

    In the test setup, the DP30V5A is set to source 10V at a maximum of 5A. It’s connected (via a multimeter in 10A current measurement mode) to an electronic load set to consume 1A. Both the multimeter and load report a current consumption of 1A, but the DP30V5A reports only 0.29A.

    After sketching everything out, it became obvious that this was due to the low-side current sense resistor only seeing some of the current flow, and the rest flowing through the unused LM2596 modules (the switch A represents the internal connection between the DP30V5A 0V and the fixed rail 0V)

    Disconnecting the 0V rails and providing a separate 0V binding point for the fixed rails fixed this issue, and I’ll just have to keep in mind that if I want to use multiple rails from this mini PSU in the same circuit, I can’t trust the DP30V5A current reading and have to set its maximum current to about 33% of the desired value. Otherwise, the software overcurrent protection can’t function correctly, and there’s a risk of damaging both the module and the circut under test.

    An amusing side effect of this setup is that the DP30V5A low side current sensing can be used for the fixed rails! I doubt I’ll ever encounter a situation where this is useful though.

    More about high and low side current sensing in this AAC article

  2. That first one was definitely the funniest, but the some of the other bowl-demons are pretty great too.

    There’s a bit more detail about exactly what’s going on in this article.

    I’m surprised how timeless and appealing these little drawings are. They avoid a lot of the foibles which make a lot of late antique/medieval art look dated, and the exaggerated proportions, noodly limbs and googly eyes wouldn’t be out of place in a webcomic or cartoon.

    I also love that these bowls refer to themselves as “amulets”. Next time someone describes something as an “amulet” in a novel or TTRPG I’m definitely going to imagine it as an inverted bowl with a googly-eyed stick figure demon on.

  3. I’ve wanted to see an Alpine Rosalia ever since I first heard about them, and finally managed to spot two today! Very impressive beetles, lots of fun to watch them move, and they make a cute little scratching sound when disturbed.

  4. Thinking a pigeon is a bird of prey, because it’s perched in a tree, is easily my funniest iNaturalist computer vision fail yet.

  5. PHPUnit’s HTML code coverage reports don’t play nicely with GitHub pages “main branch /docs folder” by default, as they store CSS, JS and icon assets in folders prefixed with underscores.

    Here’s a little bash script to run tests with code coverage enabled, then move the assets around:

    rm -rf docs/coverage/
    XDEBUG_MODE=coverage  ./vendor/bin/phpunit tests --coverage-filter src --coverage-html docs/coverage
    mv docs/coverage/_css docs/coverage/phpunit_css
    mv docs/coverage/_icons docs/coverage/phpunit_icons
    mv docs/coverage/_js docs/coverage/phpunit_js
    grep -rl _css docs/coverage | xargs sed -i "" -e 's/_css/phpunit_css/g'
    grep -rl _icons docs/coverage | xargs sed -i "" -e 's/_icons/phpunit_icons/g'
    grep -rl _js docs/coverage | xargs sed -i "" -e 's/_js/phpunit_js/g'
    

    That allows you to use GitHub pages to show code coverage reports as well as docs, as I’m doing for taproot/indieauth.

  6. Some more hamster activity today! Anyone have any idea what the behaviour at 0:57 is? Looks like it’s trying to flatten grass, but I imagine it’d rather rest in its hole than on the surface.

    Update: based on discussion in this thread, looks like it’s probably scent-marking after a territorial dispute with another male.

  7. Ridiculous amounts of hamster activity at the moment. I must have seen nearly 100 of them in an hour. I also heard them vocalise for the first time, a sort of guttural hissing sound.

  8. Tip for anyone using greg to download podcasts: this config setting forces the downloaded files to be in chronological order, and strips any query parameters from the end of their name:

    downloadhandler = wget {link} -O {directory}/{date}_{filename}
    

  9. Had some fun looking at soil with a cheap USB microscope today. At maximum magnification, its depth of field is smaller than the height of one of these tiny soil mites (maybe 0.3mm at the most)