The phantastic kit "Expeyes-Junior" has several ADC. Thanks to the
Expeyes Python library simple Python programs can read and process the
data. The GUI aready has a module which records characteristic lines of
diodes, including a fit program.
Unfortunately the fit program was designed for Si diodes only. It seems
to restrict the so called emission coefficient n -- a correction factor
in the denominator of the exponent -- to values between 1 an 2.
In the attached diagram you find a measurement indicated by crosses. The
Expeyes fit program fails to fit the data. Least square fit programs
have problems to find the right fit, see solid line in upper diagram
(which was generated by other tools).
I tried a lot to find a fit for light emitting diodes. In the end it was
very simple: remove the restiction for n and perform a linear fit of
logarithmic data.
Please find the result in the lower diagram. The measurement (crosses)
fits well with the calculated exponential curve (solid line) with only
two fit parameters:
i= 7.8e-10
n= 4.8
Unfortunately I don't have a deep knowledge about the program structure
of Expeyes libraries.
Question:
Do you know who is familiar with Expeyes diode fit program? Is it
possible to extend the fit program in order to fit not only Si-diodes
but LED as well?
Andreas
Attachment:
greenled.jpg
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