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. 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.

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

  4. 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.

  5. 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)

  6. After many unsuccessful attempts to propagate shrub cuttings, this sage seems to be cooperating! Making a tape grid over a plastic tub of water is a nice low-tech solution for holding many cuttings upright.

  7. Day 4 of the was very successful after the storm-related inactivity of day 3, with 106 observations from the Lobau and Prater. Highlights include:

    My first sighting of wild european pond turtles

    My first black woodpeckers

    Many great spotted woodpeckers

    A greater bee fly which held still long enough for me to photograph it

    Some newts

    This interesting spider

    These enormous beetle larvae

    This cool looking moth

    And many, many oil beetles

    That makes a total of 213 observations over the long weekend. It’ll take some time for them to be identifed down to species level, but it looks like at least 130 individual species.

  8. Day 2 of the : I finally made it to the Lainzer Tiergarten and made 73 observations, the highlights of which included:

    Some enormous woodlice

    Some sort of Polydesmus, curled up on a little wall it had built to protect its eggs

    Plenty of Glomeris and pill woodlice

    A red squirrel

    A nuthatch — not a great photo, but they’re one of my favourite woodland birds

    One of the furriest moths I’ve ever seen — I think it’s a chimney sweep moth? If so, it’s an appropriate name.

    And finally, this enormous severed stag beetle head.

  9. Made 34 observations on the first day of the Wien. Nothing particularly remarkable, except for the biggest frog I’ve ever seen, and lots of hamster activity, including some fights and parents with young, which I’ve not seen before.

  10. Today I realised I had never taken any good photos of this mountain dulcimer I built in 2016 as a warm-up project after moving to a new workshop.

  11. The 70s got me covered if I end up getting quarantined due to coronavirus. Unopened and in mint condition, I can rely on McDougall to see me through these hard times