This is the new link: https://ibtk.de/project/remote/UCR2-IR-Booster.pdf
Thank you, kennymc.c!
Hello Wotan, You may use DeepL.com to translate it easily.
Cheers, Tiki
This is of great interest to me. Thanks for all the great research. Apparently, the main problem with driving the Harmony blaster with the UC dock is that the Harmony incorporates its own internal limiting resistors and they are too large for what the UC dock supplies. You recommend shunting them with smaller resistors so that the parallel combination makes the desired value. I will look into how to take these apart non-destructively (I have spare ones I got from eBay). The DIY LED array is also of interest. I had not thought much about the angular distribution of a bare LED, only that it’s not likely to be uniform over 4 Pi. Maybe some optics could be tried to even further optimize the radiation pattern.
Also, thanks for the translation link. My last formal course in German was in the 1970’s I tried, but there were many points I had missed trying to read it on my own.
A good joke I read recently in a New York Times editorial: if someone who speaks two languages is bilingual and someone who speaks three languages is trilingual, what do you call someone who only speaks one language? Answer: American. Guilty as charged!
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@Tiki, I have some questions about your IR booster article:
Your original array of 6 SFH4346 diodes in series-parallel, is plugged into a 3.5 mm jack of the UC2 dock with no modifications to the dock itself, correct? Could two such arrays safely be plugged in, one into each 3.5mm jack?
To plug a Harmony blaster into the UC dock and achieve greater IR power while keeping the current at a safe level you shunt each 8.2 resistor in the blaster with 24 to 27 ohms, correct? No modifications to the UC dock itself in either case? This only drops the resistance in each leg to about 6 ohms. Could a so modified Harmony blaster be plugged into each UC jack without exceeding safe current of the MOSFET? Or would the resistors inside the blasters have to be modified accordingly? I would simply replace the 2.5mm plug on the Harmony with a 3.5mm TRS to avoid mixing them up with blasters that still plug into the original Harmony. I have some spares.
I’m not interested in either drilling a hole on top of the dock or sticking a diode on top of the dock and cabling to the inside because I prefer to keep the placement of the emitter flexible.
I understand the basic principles of calculating the currents but am having some difficulty following your calculations in detail. Maybe something is lost in translation.
Thanks for all the research and effort that went into this article.
Hello Wotan,
In the dock, the drain resistance in the driver stage is lowered by parallel connection. In my case on only one output, the other remained unmodified.
The original value is 68 Ohm, the resulting value (in my case) is about 3.0 Ohm. The exact value is not critical.
If you want to operate two blasters with the dock, both 68 Ohm resistors must be bridged with e.g. 3.3 Ohm each.
I did not make any changes to the Harmony Blaster.
With the original Harmony Blaster, the 68 Ohm resistor in the dock should be bridged with about 18 Ohm for a similar operating current. I accidentally left out the current distribution in the PDF-document.
If you do not change the resistors either in the dock or in the Blaster, the result is about 17mA per diode branch - much too low.
Even short-circuiting the Harmony Blaster resistors (with unmodified dock) results in only about 18mA each.
Background:
The original operating voltage of the blaster is 3.3V.
The voltage across the 2 LEDs in series is approx. 2.55V (=1.275V each).
The residual voltage across the 8.2 Ohm resistor is approx. 0.75V.
This means that the LED current per branch in the original is 0.75V/8.2Ohm = 91mA, the total current is 182mA.
The operating voltage in the dock is 5V.
According to the data sheet, the Mosfet can handle 5A(?) and has an RDSon of ~50mOhm.
In the case of the dock plus Harmony Blaster, with the operating voltage of 5V and in the original state we get (both LED branches in parallel):
I*(RDSon + RD(Dock) + 1/2R(Blaster)) + 2VF(LED) = 5V
when rearranged, the total current is
I = 5V - 2VF(LED) / (RDSon + RD(Dock) + 1/2R(Blaster))
I = 5V - 2*1.275V / (50mOhm + 68 Ohm + 4.1 Ohm) = 34mA (= 17mA per branch)
Conclusion:
The Harmony Blaster connection is only useful if the dock (RD) is modified.
Cheers, Timo
Thanks for that clarification. Does the entire rubber foot have to be peeked off to gain access to the screws to the bottom? I was a little reluctant to do that, fearing I wouldn’t get it to lie flat again without removing the old glue and re-gluing it. It looks like maybe it was designed so that the bottom can be slid along the slots to clear the screw heads and rear jacks without completely removing the screws. It is difficult to see from the picture where the modification has been made but it looks like some work was done at the upper left corner. I will figure it out when I get it opened up. Thanks again.
p.s. it turns out the IR LED you used for your array is obsolete and no longer available (according to Digikey and Mouser) in favor more efficient diodes. One with similar operating current and wavelength looks like it has about 10X radiated IR power, which seems suspicious to me. I must be missing something.
Hello Wotan,
you may have a look into the PDF again, page 2.
The photos 3.x show the position of the screws. Check the orientation, please.
I carefully lifted the edges of the rubber only at the approximate locations of the screws.
The glue should remain on the rubber, if you avoid extensive touching it.
The screws remail in the plastic cover.
Yes, the SFH4346 seems to be obsolete.
One should use one IR-LED with a very wide viewing angle and higher current capability instead. The Osram SFH4726AS A01 was my choice, which is functioning properly.
The observed raise (~2 times) in optical power at a given current is correct, due to the double layer design, which results in a higher operating voltage too. The optical power per steradiant is a different number, dependent on the viewing angle, of course.
Check the table in my document, if interested.
Cheers, Timo
Hi Tiki !
Would such thing work connected to the dock jack output ?
https://learn.adafruit.com/adafruit-high-power-infrared-led-emitter
Hello!
Buy and try! It‘s so cheap.
The IR-LED is not that powerful and exhibits a narrow beam angle only. So it won‘t fit the requirements for a reliable repeater in my opinion.
I explained the reasons in my (German) document, which you may have found already.
Good luck!
Cheers, Tiki