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Optical detectors

Posted by Jacques (A) on August 25, 2006 at 01:55:22

In Reply to: Parts for a distance-sensing auto-tonearm-lift? posted by Ronnie Ericsson on August 24, 2006 at 14:47:58:

As for distance-sensing optos (other systems are possible), you have 2 types:

1. by reflection : a light beam is focused on a point in space, if a piece of a reflective material passes in front of it, you get a signal.
   Advantage: easier to mount, with wider tolerance than transmission.
   Drawback: I don't see.
2. by transmission (fork type): a light beam is intercepted when a screen passes in front of it.
   Advantage : easier to figure out what's goinbg on.
   Drawback: trickier to mount for a DIY, since the body is in two big parts, one on each side of the screen (I call "screen the small piece of metal that moves with th turntable arm.)

Among the reflection types: (values in parenthesises separated by a / are possible choices, for example HOA70(8/9)-001 means HOA708-001 and HOA709-001 ) detection distance = d
Honeywell:

HOA70(8/9)-001 d=3,18mm
HOA140(4/5)-002 d=5,1mm
HOA149-001 d=3,8mm
HOA1405-002 d=5,1mm
HOA1180-003 (with wires) d= 12,7mm

Sharp: GP2D150A (with embedded electronics, d= 30 to 300mm!)
Optek:

OPB702 d=3,81mm
OPB715 d=12,7mm
OPB760T d=2mm

Among the transmission (fork) types (l= width between fork legs):
Honeywell:

HOA1873-0(12/13) l=2,5mm
HOA1874-0(12/13) l=3,1mm
HOA1877-0(12/13) l=9,5mm
HOA0880-T51 l=9,5mm (wires)
HOA200(1/3/5)-001 l=3mm, Schmitt trigger (good)

OSRAM SFH93(01/40)l=3,4mm
OPTEK

OPB360T1 l=3mm
OPB815L l=3mm
OPB360T1 l=10mm
OPB830L51 l=3mm

BTW, to give a touch of 21st century modernity to your 20th century tonearm, have its autolift made from recycled parts: you will find excellent detectors in obsolete printers! (paper detector, end of carriage)
On old printers of the '80s (metal framed), you will get setting screws, plates and the like to help you mount and adjust the thing. Ask any computer store.
You could also use an old mouse, many of them use optical detection of a radially printed wheel. But it's too much specific (double detectors to detect direction of change, too much small fork etc) perhaps.
The printer's is the best idea.
I would warmly encourage you to use those recycled detectors!
And buy one or two DVDs with the saved money.
If the idea of using recycled detectors rebuts you (why? but you're a free man... ), you can find all those listed above at Radiospares or Farnell.
Prices between 5 and 12 euros.

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