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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:
- 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.- 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
OPTEKOPB360T1 l=3mm
OPB815L l=3mm
OPB360T1 l=10mm
OPB830L51 l=3mmBTW, 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.
Follow Ups:
I thing the fork type looks good for the application.
No need to attach a reflective surface, and no risk of engaging the lift by mistake!
Just takes a little "screen" thing to stick out from the arm (or perhaps use the whole arm tube for the screen).I'm no good with transistors. What supply voltage range does the transistor in this one like (see link)?
30V is the absolute max value. 24V is the practical max value.
With 24V:
Use a 33kohm resistor as collector load, you'll get about 0,6mA collector curent when on, which is fine.
As for the LED, use a 2,2KOhm resistor in serie with the anode. You'll get 10mA LED current, which is fine.I would advise you to use some timer (a simple 555 would make the job fine) in order to get a pulse with a predetermined duration, which would be used to lift the tonearm.
In this case, have the voltage at about 12V. Decrease resistors in accordance.
Does that mean the transistor switches abruptly between 0mA (OFF) and 0.6mA (ON)?I was thinking of driving some kind of motorized ball-screw actuator (directly off the transistor if possible). Perhaps some kind of minimotor..
Does that mean the transistor switches abruptly between 0mA (OFF) and 0.6mA (ON)?
was thinking of driving some kind of motorized ball-screw actuator (directly off the transistor if possible). Not possible: you won't get more than 0.6mA from the phototransistor, which is way too small to move an actuator.
Perhaps some kind of minimotor..
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