Hoefer DNA Fluorometer TKO-100 tear down and schematic

Graham Wideman

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Sep 27, 2015, 4:06:05 AM9/27/15

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Some documentation on the internals of the Hoefer TKO-100 DNA Fluorometer, including a schematic diagram of the circuit board.

Still looking for an operator's manual!

http://grahamwideman.wikispaces.com/Hoefer+Fluorometer+TKO-100

This is informative beyond this specific unit, as it shows an example of a "lock-in" amplifier, a design used for detecting weak signals in the presence of noise.

- Graham

Cathal (Phone)

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Sep 27, 2015, 4:55:05 AM9/27/15

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Great work Graham, thanks for sharing! And serious kudos for the circuit diagram. How hard would it be to adapt this to SybrSafe, do you think?

DIY Fluorometry might be a better bet than full UV-Spec, given the complexity of building DIY diffraction repeatably and the cost of monochromatic UV LEDs in the right wavelengths..

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Nathan McCorkle

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Sep 29, 2015, 2:42:47 AM9/29/15

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I second what Cathal said, Great work and thanks for sharing!

Now for a question. Are you sure it would be considered a lock-in
amplifier, and not just a common-mode offset adjust/subtract?

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-Nathan

Graham Wideman

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Sep 29, 2015, 3:29:09 AM9/29/15

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Hi Nathan:

At this stage I've fairly convinced this is actually not a lock-in amplifier. I noted that in the article accompanying the schematic, but after I posted to this list.

The key clue is the filter on the "lamp" input -- too low a cutoff frequency to be passing 60Hz. So the remaining conjecture is that the fluorescence reading simply gets divided by the lamp value to get a result that's more or less independent of lamp brightness.

So the function at the MAT04 "multiplier" stage would be conceptually:

i = antilog( log(fluorescence) - log(lamp) ) or

i = fluorescence/lamp

There might be some confusion around the polarity of the signals when they arrive at U4C which combines them, given that the light measurement signal passes through two inverting stages in the case of the lamp, and three in the case of the fluorescence.

However, we don't know the polarities of the photodetector connections and they may the same or opposite to each other.

So, this is not an entirely settled matter at this point.

I guess I'm just going to note this, and change the annotations on the schematic a little to reflect the uncertainty, since our unit's UV lamp (or the 1200V transformer) is broken preventing an actual test.