First, thanks for posting the schematic for the board in another thread, very helpful! (http://forums.adafruit.com/viewtopic.ph ... va#p286893)
Next, I'm attempting to resolve some discrepancy between the datasheet and the board description in the calculation of UVI. Bear with me, hopefully I've just made a dumb mistake in my math...
I'm powering the board with 3.3V.
From the DS, 1e-6A ~= 9mW/cm2. Using our good old friend from grade school y=mx+b, the line for UVA power is ~ y = (1.1088e-7)x
It looks like from the UVI graph the line is y = (2.1e-8)x + 7.3e-8. This is using UVI 6 = 2.0e-7A and UVI 15 = 3.9e-7A, but this doesn't really jive with the DS Iph value above the graph of 2.6e-8A for UVI 1. Just eyeballing their graph, UVI 1 ~= 1.0e-7, so this makes no sense to me at all.
From the schematic, the opamp is set to a gain of 1e6, correct (R1)? So 1e-9A input would give an output of 0.001V, or 1V/uA gain.
If the gain is 1V/1uA then I'm not sure how the formula given for the breakout board makes sense: Vo = 4.3 * Diode-Current-in-uA
Do R2 and R3 effect the gain calculation, or are they signal filters?
Here are my calculations based on my line equation for the UVI, where the heck am I going wrong?
THANKS!
Z
Code: Select all
UVI Photocurrent(A) output voltage V @1V/uA
0 7.30E-008 0.073
1 9.40E-008 0.094
2 1.15E-007 0.115
3 1.36E-007 0.136
4 1.57E-007 0.157
5 1.78E-007 0.178
6 1.99E-007 0.199
7 2.20E-007 0.22
8 2.41E-007 0.241
9 2.62E-007 0.262
10 2.83E-007 0.283
11 3.04E-007 0.304
12 3.25E-007 0.325
13 3.46E-007 0.346
14 3.67E-007 0.367
15 3.88E-007 0.388