episode 19: hand-held scopes, disassembling scales, and a digital probe

(First of all, apologies for the many "uhhh"s and "ummm"s you can hear - no idea what was going on there. Edited out a lot, and next time it should be better.) Topics this time are my effort so far for the RetroChallenge 2018/04 (25% in), a short and biased discussion of some available handheld oscilloscopes, disassembling consumer-scales to see what was going on inside, hacking together a small digital probe to distinguish high/low/floating pins, and blowing a fuse while poking at electronics. --- Links/show-notes, in that order: my effort this week for the RetroChallenge 2018/04 (April) some portable scopes: the ones I used: Velleman HPS140i (1-channel) Velleman WFS210 (WiFi, 2-channel) Seeedstudio DSO Nano v1 (1-channel) nice but starting from approx EUR 400: Owon HDS series Micsig tBook series Siglent SHS series PC-based: Owon VDS series LabNation SmartScope (software any good..?) Awesome Space retro-place (Utrecht, NL) Makersbase fablab (Breda, NL) Hackalot hackspace (Eindhoven, NL) W.r.t the blown fuse: I made the rookie mistake of connecting probe-ground to something main-referenced (but not earth)... #makeagoodfirstimpression --- Some pics of scales-disassembly: (load-sensor mounted in one of the scales' 4 feet) (strain-gauge element (?) embedded in metal spring-thing) Note that when the metal thing is flexed, both "halves" of the element would decrease in resistance - a few hundred Ohms when flexing them by hand. That's why I don't understand why there were 3 wires bonded to this thing. Why not use 2? (From what I read and discussed with a friend, one "half" would ideally have to have a constant or at least less-decreasing-when-flexed resistance, to be used in a Wheatstone bridge.) --- Schematic and pics of the digital probe: (probe in a blob of hot-glue)