From: Jason v. N. <ja...@vo...> - 2005-01-10 21:09:43
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Hi all. I've seen some discussion on the list regarding pullup resistors for the I2C bus and I'm going to be experimenting with this some tonight. I don't see a place on the Gumstix or Waysmall board where I can easily get at 3.3v without some serious surface mounting skills that I don't possess. What I was thinking of doing, and I'm sure this will make the real engineers in the audience cringe, is using one or two of the other available GPIO lines on the Waysmall as a pull up power supply. I'd just add a few lines to my init scripts to set the lines as output and then have the resistors go from those lines tied together to the I2C bus lines. So, my question is whether this is a terrible idea or not? I know it's not ideal but my resources are limited. If someone has a better suggestion as to how I can get the I2C bus working without extremely precision soldering I'd love to hear it. Jason |
From: Dave H. <dhy...@gm...> - 2005-01-10 22:00:40
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Hi Jason, On Mon, 10 Jan 2005 15:09:39 -0600, Jason von Nieda <ja...@vo...> wrote: > Hi all. I've seen some discussion on the list regarding pullup resistors > for the I2C bus and I'm going to be experimenting with this some > tonight. I don't see a place on the Gumstix or Waysmall board where I > can easily get at 3.3v without some serious surface mounting skills that > I don't possess. What I was thinking of doing, and I'm sure this will > make the real engineers in the audience cringe, is using one or two of > the other available GPIO lines on the Waysmall as a pull up power > supply. I'd just add a few lines to my init scripts to set the lines as > output and then have the resistors go from those lines tied together to > the I2C bus lines. I'm pretty sure that the voltage regulator on the waysmall board is3.3v. You can see the schematic here: http://www.gumstix.org/tikiwiki/tiki-index.php?page=POWER_JACK In this picture: http://www.davehylands.com/linux/gumstix/Case-Fit/HPNX0079.html the voltage regulator is the little five pin chip immediately to the left of the power supply, and the top pin on the side with just two pins, would correspond the 3.3v signal (You should check with a multimeter to be sure). You should be able to solder a wire onto there to get your 3.3v. -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/ |
From: Jason v. N. <ja...@vo...> - 2005-01-10 22:09:36
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Dave Hylands wrote: >In this picture: >http://www.davehylands.com/linux/gumstix/Case-Fit/HPNX0079.html >the voltage regulator is the little five pin chip immediately to the >left of the power supply, and the top pin on the side with just two >pins, would correspond the 3.3v signal (You should check with a >multimeter to be sure). > >You should be able to solder a wire onto there to get your 3.3v. > > > Thanks for the response Dave. I was looking at that spot last night as I figured it was the regulator. My concern was that I wouldn't be able to solder a wire on there and get a good connection without making a big mess of the board. Maybe I just need to buy a better soldering iron and do some practicing :) To satisfy my curiosity, would my idea of using one or more GPIO lines bridged have worked? I can't think of any reason it wouldn't, but my experience is fairly limited. Jason |
From: Dave H. <dhy...@gm...> - 2005-01-10 22:27:37
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Hi Jason, > To satisfy my curiosity, would my idea of using one or more GPIO lines > bridged have worked? I can't think of any reason it wouldn't, but my > experience is fairly limited. If I'm reading the data sheet correctly, the GPIO pins are rated upto 5ma. So at 3.3v, this would require a resistor (V=IR, so R = V/I = 3.3/0.005 or 660 ohms or greater. The datasheet shows 4.99K pullup resistors being used with the i2c, so this would mean that only 0.7ma would be required. So yes, it would seem that using a GPIO pin should be fine (unless I'm overlooking something), although personally, I'd be alot more comfortable using a 3.3v supply. I don't have my waysmall board with me, but I'd also look for some vias. These are generally easier to solder to. The Vcc from the regulator goes over to the two chips for the RS-232 level shifting. Dave Hylands |
From: Dave H. <dhy...@gm...> - 2005-01-12 18:39:04
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Hi Jason, On Mon, 10 Jan 2005 16:09:29 -0600, Jason von Nieda <ja...@vo...> wrote: > Dave Hylands wrote: > > >In this picture: > >http://www.davehylands.com/linux/gumstix/Case-Fit/HPNX0079.html > >the voltage regulator is the little five pin chip immediately to the > >left of the power supply, and the top pin on the side with just two > >pins, would correspond the 3.3v signal (You should check with a > >multimeter to be sure). If you look at this picture: http://www.davehylands.com/Misc/gumstix/Gumstix-3.3v.JPG I circled the via on the far right in blue. This trace connects to the 3.3v signal from the regulator, and should be a much easier place to solder to. If you use a fine enough wire, you should be able to poke it right through the via once the solder is liquid. -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/ |
From: Jason v. N. <ja...@vo...> - 2005-01-14 15:18:44
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Dave, I finally got a chance to try this last night and it looks like that via will work perfectly. Thanks for the tip! Jason Dave Hylands wrote: >Hi Jason, > >On Mon, 10 Jan 2005 16:09:29 -0600, Jason von Nieda <ja...@vo...> wrote: > > >>Dave Hylands wrote: >> >> >> >>>In this picture: >>>http://www.davehylands.com/linux/gumstix/Case-Fit/HPNX0079.html >>>the voltage regulator is the little five pin chip immediately to the >>>left of the power supply, and the top pin on the side with just two >>>pins, would correspond the 3.3v signal (You should check with a >>>multimeter to be sure). >>> >>> > >If you look at this picture: >http://www.davehylands.com/Misc/gumstix/Gumstix-3.3v.JPG > >I circled the via on the far right in blue. This trace connects to the >3.3v signal from the regulator, and should be a much easier place to >solder to. If you use a fine enough wire, you should be able to poke >it right through the via once the solder is liquid. > > > |