I have to say I am pretty satisfied with the outcome, despite the ugly start. With the diode in there, my interface circuit is now as perfect, safe and cheap as it can be with the available information, and still easy to use. The divider-approach suffers from a number of problems: - You have to get ...

Well, we also could have ended up with a chip by a competitor and the full data-sheet, see for example the Beagle Bone. But, yes, I do not know how the decision was reached either. You have your opinion about the data-sheet and I have mine. Let us just leave it at that, shall we? BTW, I do not think...

As I cannot really rule out that Broadcom ships chips with defective I/O protection (there must be a reason they are sitting on this info after all...), here is the updated circuit: http://www.tansi.org/rp/1k_02.gif Properties: * Interfaces 5V logic safely * GPIO pin stays at or below 4.3V, the "Liz...

You misunderstand the current state-of-the-art. There are basically no "unprotected I/O pins" today. These were used very early in CMOS history and died so often that they completely went out of fashion. Nobody uses them today, except in very very special circuits. There are no "unprotected" pins fo...

I am aware of that effect. I admit that I should have limited the statement to well-designed I/O cells. (We are deeply into nit-picking now...) In any reasonable I/O cell design this effect will be under control and not play a role. Of course, it is possible that the Pi SoC has broken I/O cells that...

Interesting world-view you have there that quoting your statement back to you is "disrespect" and "ego". I advise a long, hard look into the mirror. Anyways, no need to revise what I wrote (months ago) about interfacing the Pi to 5V logic. As to the issue of pull-up persistence, I will look into aga...

Thanks for the confirmation. Care is always advisable, hence I have the 1k resistor in my advice on how to interface 5V. If you only use it as input, using a larger resistor or a divider is fine. If you want to use it as input and output, then 1k is exactly the way to go. This still results in almos...

As to pullup-state: This is not a "misunderstanding", it is a measurement. i.e., an observation. I did remove the power for the tests. It is possible these are indeed latches and that the latches have a very low holding voltage or are powered for some additional time by some internal capacitor. Will...

@jojopi: Several points. 1) I assume you connected your digital multimeter between 5V and a Pi output. That is not a test for a protection diode. 10M is far to high, that could be any kind of leakage. Repeat with 10k or 3K3 and you get a real test. (No, you will not blow the diodes. They are an inte...

As to the question why the FET-based level-shifter work: That is a bit advanced. I suggest reading the original application note by Phillips (now NPX), mirrored here: http://www.adafruit.com/datasheets/an97055.pdf After that, run through all 4 cases in your mind, with the other side just having the ...

@mahjongg: I completely agree to your analysis for the case that there is an upper protection diode. (Except that 1.2mA is not something that will overload a protection diode. They are also protection against crosstalk and typically can tolerate 10-20mA permanently.) I included the 1K resistor preci...

If I understand this correctly, the opto-couplers are supplied from 3.3V in your scenario. If so there is a possible problem if the LEDs in the opto-couplers require more voltage or current to operate reliably. If I see this right, the opto-couplers are PC817. The LED in the PC817 takes something li...

I was just replying in kind, deducing this was the normal style here. I see I deduced wrongly. Hence to I apologize for my tone and thanks to the moderator for allowing my reply anyways. In case anybody wonders about why this circuit works, _after_ reading the explanation on http://www.tansi.org/rp/...

Impressive. Most clueless posting I have read all week. Have you even bothered to read the analysis that lead me to the conclusion that for the I/O pins specifically on the PI this circuit is fine? No, you apparently have not! :x :x :x Your generic "explanation" is not only factually wrong, IT DOES ...