Tuesday 12 August 2008

CT chip vagaries solved

In an earlier posting I made mention of some problems with CV values in CT Elektronik DCX74 chips. I've now got much further towards a solution. The main lessons being:
  1. check carefully which decoder files are used in DecoderPro, some of the CT files are for very old versions of the chips which have different CV layouts. Using those can make a newer chip go haywire.
  2. the mapping of half-speed mode to a function key isn't well documented for the DCX74. It is in the DCX75 (German) manual, and there are DecoderPro files available on their JMRI users Yahoo group. With luck the files will find their way to a release version of JMRI/DecoderPro in due course.
  3. the movement behaviour for uncoupling is different to that by Zimo. Loco movement seems to be triggered on "function off" rather than "function on". I haven't found a setting which will trigger the operation of a coil at the correct place in the operating sequence. Consequently, I think it will end up as a two function uncoupling sequence; the first to "open" the coupler, the second to move the locomotive. ( Update, December 2008 ; I have now deciphered the CT movement behaviour, and it does all the tricks ! See the 2mm scale 04 elsewhere in the blog. I have updated the JMRI/DecoderPro definitions file to make this considerably less cryptic. ).

Sensibly priced close up photography.

Taking closeups does not require expensive kit, just a bit of thought.

These two pictures are of a 2mm scale wagon with 3 link chain couplers. To give an idea of scale, the wheels are 6mm diameter, the track gauge 9.42mm.

Camera is a Canon A710is, which is a typical Canon compact camera. The additional "magic" bits are:
  • Lighting box from Jessops; essentially a foldup white fabric box with a blue curved backcloth. Bright lamps are placed outside the box, and the fabric ensures a uniform light within the box.
  • Closeup lens. Canon accessory lens holder for A-series camera (about £17 from Canon). x4 screw-in closeup filter (about £4 from 7-day-shop). I also have a x2 filter lens. These allow the camera to focus closely whilst on maximum zoom and stood back over 30cm from the models. In turn, this means there is minimal barrel distortion caused by having the camera in "macro" mode a couple of cm from the subject.
  • Tripod to hold camera.
  • Camera setup: Manually set the whitebalance. Set film type to slowest available (typically 80 ISA). Set aperture to minimum, and let camera choose speed. Focus manually (at least check where any auto focus is locking!). Use timer-release option on camera to avoid any shake. If not sure about exposure, its worth trying with +/- a small amount of "EV" compensation.