Gemini* and Gopher

• Personal/Opinions

  • Enigma

  • Repairs

    I've managed in the space of the past month or so to find the time to get quite a bit of assorted repair/maintenance work done. Some of these tasks are things I've been putting off for a while, others were responding to things as they happened. Once the ball got rolling I kind of got into the mindset and it became easy. Well, actually, it wasn't a ball I got rolling, but rather a wheel! The first task was replacing the bearings in the back wheel of the Franken Peugeot, which I had been putting off for a very long time.

    The mirror bumper in one of my Pentax ME-Supers had degraded to the point where the mirror sometimes gets stuck up on the gooey foam stuff. I bought a replacement bumper off eBay. Removing the old one was a bit of a chore. I got it all off, but not without making a bit of a mess of the focussing screen in the process. I want to clean that up nicely before I install the new bumper. Oh yeah, remember one million years ago when I bought a cheap Pentax MX? I still haven't put a single roll of film through it because I haven't gotten around to replacing the light seals on it. So I bought a kit for that from the same seller at the same time, so maybe that'll happen sometime soon as well. The light meter in my other ME-Super died abruptly in the middle of a holiday about a year ago, I still need to look into that some time.

• Politics and World Events

  • The Wisdom of the Crowds

    Some context here is that the Spartan king (one of them, they had two because reasons) had said "yeah, no" about an expedition, however possibly profitable (Aristagoras having gotten himself into this mess by screwing up an in theory profitable operation that had left him deeply in debt), that would have taken the Spartan army three months away from the sea. For all their supposed might the Spartans were mighty shy about actually going out to fight on many occasions, possibly because the helots would (and did) revolt if they looked away for more than two seconds.

• Technology and Free Software

  • AC Explorations - Continued

    The LM368 circuit I built recently does not handle quite as much current as I was imagining. I had misread figure 3 in the data sheet, which indicated a plateau of about 3.7 V output voltage with a 4 ohm load. The units for that are peak-to-peak, meaning the RMS value would be 3.7 / 2 / √2 or about 1.3 Vrms. With a 5.7 ohm resistor I was seeing about 1.65 Vrms on the output, before the peaks of the signal started getting chopped off. So, max RMS current would be around 300 mA with the 4 ohm resistor.

    Of course, if you are just making measurements, and not trying to heat something up, then one could deal in max voltage and max current, i.e., the peak of the cycle. And 300 mA RMS current would be over 400 mA peak which is decent current for my purposes.

    For experimentation, I connected this circuit to a LCR network with a 470 nF cap and a 1 mH inductor. Together, the cap and the inductor had 16.5 ohms internal resistance. By my calculations — which I have not double checked — that should be a resonant frequency of 7420 Hz and, and a peak current of 137 mA, assuming an output voltage of 1.6 Vrms or 2.26 Vp-p, which I picked so I wouldn't have to tweak my signal generator settings. The frequency 7420 gives a reactance of 46.6 ohms on the inductor (2 pi f L) and I assumed the same reactance on the capacitor since we are at resonant frequency. Assuming no mistakes so far, that should give us a peak voltage across the capacitor or inductor of 0.137 A × 46.6 Ω = 6.39 V.