[Bio] early findings for NIR probe

[Rolf]

Hi again folks!

I got the new OP506 phototransistors from my friend late last night.
He was nice enough to combine with his order and save us the shipping costs.
(these parts costs 0.80 each.. shipping would be much more)

I just had a chance to test one quickly.
So far, it looks pretty encouraging.

The setup is an 850nm IR LED pointing at the phototransistor, about 3-5 cm away.
I can get a range of current from 0.02mA (nearly dark) to 3.80mA
(directly lighted)
through the phototransistor.
3.80/0.2 is 190.  The light/dark ratio is more than 2 orders of magnitude.
I'm not sure, but I think that means we should be able to measure optical loss
for 2 orders of magnitude as well.
Optical loss is related to Absorption.

There is still the challenge of making a holder for these two parts,
especially one
that we can dip into a liquid culture.
The two devices look like 3mm LEDs each with two wires coming out.
Any ideas?

We also want to come up with a way to calibrate it.
Perhaps by starting with distilled water?

Let's definitely talk more about it at Monday's meeting!

Cheers,
-rolf