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confusing voltage descriptions for USB BUB II

Posted: Sun Mar 31, 2019 3:14 pm
by WJCarpenter
I bought a USB BUB II a long time ago, but I just got around to soldering on the headers and trying to figure it out. The version I have is slightly different than the one currently pictured on the USB BUB II product page. The silk screen printing on the back side does not say "v1" (or any version at all), and it doesn't admonish me, like Highlander, that of solder bridges "There can be only one!"

Maybe it's because of the older version, or maybe I am just dense, but I can't quite grok the instructions for selecting the output voltages for power (VOUT) and logic (LGLV). In the universe of the USB BUB II, what exactly is or VL?

Without adding a voltage regulator, I think I want to leave the back side solder pads as-is. It says "Jumper controls VL", and there are two pairs of pads: "3v3_OUT" and "VR_OUT". It looks like there is a tiny connecting trace on the "3v3_OUT" pair (though I can't really be sure because it's so tiny). The image for the USB BUB II v1 says "solder only one". To me, that suggests my choices for the logic output are 3v3 and whatever the optional voltage regulator would produce. In other words, just 3v3 if I don't add a voltage regulator. How do I get an logic output of 5v?

On the front side, it's got two sets of 2 pairs of solder pads with an accompanying 3-pin header. One set is for VOUT and one set is for LGLV. The pin shunt positions on both are labeled VL and 5V. There are solder bridges on the pads that I assume mean they are factory "wired" to LGLV = VL and VOUT = 5V. That matches the text describing the USB BUB II v1. If I want to control things with the pins and shunts, I should remove those solder blobs from the front side.

That seems clear enough until I return to pondering the solder pads on the back side. It offers the choices of the voltage regulator or 3v3. Does that really mean "whatever the voltage regulator or whatever you choose on the front side for LGLV"? That would make sense (instead of 3v3). Or does it mean "we're fabricating this extra voltage called VL, and here are your choices for that; then on the front side, you can choose to use that or 5V independently for LGLV and VOUT outputs"? That makes sense, too, and when I use that explanation, I think all the info is actually present on the product page.

It would have saved me a lot of head-scratching if the product info page for the USB BUB II just laid out the possibilities in a table or something or had at least described in clearer terms what VL means. I could discover the truth by experimenting, but soldering and unsoldering bridges is not that much fun.

Re: confusing voltage descriptions for USB BUB II

Posted: Mon Apr 01, 2019 6:07 am
by oz

When I designed that board and wrote docs, I thought that it probably had too many options. I don't think too many people have ever tried to add the reverse side regulator. It does require cutting one jumper I remember - and hopefully that is spelled out in the docs. That is because the 3.3V output of the regulator just replaces the USB IN line for high current supply.

At the that point the logic level lines (LGLV - RX, TX and DTR) don't really make sense at 5 volts (or the use case becomes vanishingly small). So whether supplied by the regulator or the FTDI 3.3V regulator - the logic lines are going to be at 3.3 volts I believe. In any case, when faced with these kinds of options, I usually just sort them out with a meter and the schematic.

Hope that helps. I'll take a look at the docs, but I have revisited this a few times over the years.