Photo-detector to measure signal at 1 - 2 cm 1

[EddyPach]

Can comebody suggest a good photodetector that will provide a signal when mettering at a 1 to 2 cm distance from a wet surface? The idea is to measure 1 for the existence of calf skin, and zero when there is no skin. ( I am designing a skin meter).
Thanks for the advise.

 

[nbucska]

Can you tell me more ? <nbucska@pcperipherals.com>

 

[EddyPach]

I want to measure skins with an optical system, but I want to keep the measuring device at least two centimeters away from the skin (because it is wet). My idea is to place a moving bar with photo-detectors attached to it (think of a scanner). While the bar moves it sends signals to the bed where the skin rests, and when each single photo-detector &quot;sees&quot; skin, it will send a logical one to the signal processing unit, or a &quot;zero&quot; when there is no skin (the skin has an irregular shape, as we all know). After the signal rocessing unit I intent to calculate the area covered by the skin.
The proble is that most of the photo-detector that I am familiar with, have a narrow surface to surface distance.

 

[nbucska]

Radio Schack may still have a 40 khz IR optical detector.
Make an IR radiator (LED, 40 kHz osc. focusing optics ) to send a beam at 45 deg. Use the detector with narrow optics.

The 40 KHz source may be either an LC osc. or XTAL -- e.g. 1 MHz with divider.
<nbucska@pcperipherals.com>

 

[EddyPach]

Thanks nbucska. Yet,why would it be at 45 deg?

 

[nbucska]

From the horizontal position of the spot you can calculate the hight.

You can scan e.g. with rotating mirror or servoed mirror. <nbucska@pcperipherals.com>