Chuck,
(norcutt@xxxxxxxxxxxxx ) writes:
<<
Tried Radio Shack about 6 months ago but all I could get in the store or
the normal catalog were infrared devices. Went to a small, local
electronics store and bought two different types. One had a wide field,
the other was narrow. I started building with the wide field but I
think it introduces errors at high shutter speeds. I never seemed to
get any closer to the expected result than a few milliseconds. Makes it
tough to measure 1/125 or faster. I'm (eventually) going to retry with
the narrow field. I also think one needs a DC light source. In some
earlier attempts I think my measurements were picking up 60Hz noise from
the AC line. Don't really know what I'm doing so have to live and
learn.
>>
I don't know if you are using photovoltaic cells or phototransistors or CDS
cells?
Photovoltaic cells are fast enough if used in a particular way (current mode)
but in normal voltaic mode are too slow.
CDS cells are way too slow.
Most Phototransistors (as long as they are not darlington devices) should be
quite fast
enough for shutter speed measurement.
You do need to keep out ambient light. Not all things opaque to visible light
block infrared. Use a layer of Aluminum foil if in doubt.
Don't use an incandescent lamp use a high output led (red for visisble light
detect,infrared for ir detect))
Run it at it's maximum rated continuous current.
You can line up the LED/detector lenses to get approximately collimated beams
to cover a small area of the
shutter path. Choose a detector in a lensed package preffereably with a
narrow angle specification.
You can cut the width of coverage of the cell by putting it behind a drilled
hole etc.
Some general ideas for ordering components mail order/web :
There are many mail order electronic component sales operations
(some catering for amateurs) but many of the professional operations
accept credit cards and so you must just find one with a low minimum order.
For example Digikey turns your order in round in 24hrs but charges you $5 for
orders less than $25. ( http://www.digikey.com/)
See http://rocky.digikey.com/USCatalog/575.PDF
for their choice of general purpose photo-transistors.
You wouldn't want to choose devices with speeds much longer than 10us.
The lowest cost device listed the PN 168.. ($0.65) looks ok.
A smaller lens device like the PN150 might be better. ($1.05)
You probably should check the full device specs out; most electronic
vendors have full online catalogs and design notes. For example you could
check the
Panasonic website for greater detail on the parts above.
Tiny operators like Mouser Electronics don't surchage for small orders.
(http://www.mouser.com)
Often these places carry generic replacement parts from repackagers like NTE.
(http://www.nteinc.com/) (http://www.nteinc.com/Web_pgs/phototransdet.html)
Fry's Electronics in CA for example carries some of these also.
Good luck,
Tim Hughes
Hi100@xxxxxxx
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