On 03/04/2011 18:24, John Coppens wrote: > On Sun, 03 Apr 2011 16:20:08 +0100 > Oli Glaser wrote: > >> I think it's probably just to make sure of this, like the old turntable >> strobes (for speed tuning) which generally had more than one line of >> dots which were slightly offset. This would be similar for the string, >> one point being slightly offset from the other which should make it >> easier to detect relative movement. > The turntables (at least the ones I had) had different line for each > speed - 33 1/3, 45 and 78. They looked offset, but in fact did have > different number of blocks. > > John The one I had (Technics 1210 Mk2) had four lines that were for various=20 percentages of the correct speed (+3.3%, - 3.3%, +6%, 0%) The point I was trying to make (badly) is that I think it's probably=20 useful for the strobe to cover a larger area, as a vibrating string will=20 have stationary nodes where it may be hard to see any difference. Other possibilities maybe that the LEDs maybe fired 180 degrees apart,=20 or maybe even one is fired at an overtone of the fundamental.=20 Professional strobe tuners often have many overtone bands for precise=20 tuning. I had a quick look at the schematic which shows the LEDs are=20 connected to different pins, so something like this seems likely. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .