From: Tanya L. C. <tan...@gm...> - 2010-08-24 03:27:32
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Hello, I am working with the gumstix connex (now retired) and gumstix verdex pro, interfacing them to an iRobot Create over a serial port. Precisely, I'm using the verdex pro with a robostix modified to ignore its 500 mA power regulator. In addition, I'm using a wifi module to get wireless connectivity. I've been very successful in this endeavor with the gumstix connex, but I've hit an obstacle with the verdex pro. Currently, I am able to power the gumstix connex from the iRobot Create's battery using a simple voltage step-down circuit. I power the robostix and the wifi module separately since wireless requires such a big current draw. For the curious, a diagram of the circuit is here: http://kaju.dreamhosters.com/images/Images/powerdiagram.jpg I am attempting to use the same circuit to power the gumstix verdex pro from the iRobot Create's battery. Please know that the verdex pro works just great when plugged into the wall, but that doesn't make for a cool autonomous robot. Initially, using the same circuit resulted in the verdex rebooting itself again and again. I figured that the verdex has a greater current draw than the connex, so I built some custom linux images using BitBake. I'm using wireless (piggy!) so I can't turn that off. In the custom linux image, I turned off bluetooth, hoping to gain enough savings. Doing so allows the verdex to boot to the prompt and run for about 3 minutes, but then just subsequently reboots. I feel stuck. Anybody out there have any tips? I'm open to running the verdex pro using a separate battery pack, but I'd like to hear if anyone has been successful with a particular set of batteries. Sincere regards, Tanya L. Crenshaw |
From: Cole C. <chr...@um...> - 2010-08-24 07:43:17
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Tanya, I'd bet your L7805 just can't keep up with the power needs of the Gumstix. Why not try two? Excuse the "art" :) http://fittheseventh.net/powerdiagram_MkII.jpg I have done this before without a capacitor (you can tell that's supposed to be a capacitor right?) but an EE told me I should have one in there. I don't go to the trouble of actually choosing one properly because I don't think it's especially important, though probably still a good idea. I picked mine completely at random. It worked. The little verdex is almost certainly not overstressing the battery. I am almost certain it has to be the step down circuit. Good luck! -- Cole Christensen On Mon, Aug 23, 2010 at 10:27 PM, Tanya L. Crenshaw < tan...@gm...> wrote: > Hello, > > I am working with the gumstix connex (now retired) and gumstix verdex > pro, interfacing them to an iRobot Create over a serial port. > Precisely, I'm using the verdex pro with a robostix modified to ignore > its 500 mA power regulator. In addition, I'm using a wifi module to > get wireless connectivity. > > I've been very successful in this endeavor with the gumstix connex, > but I've hit an obstacle with the verdex pro. > > Currently, I am able to power the gumstix connex from the iRobot > Create's battery using a simple voltage step-down circuit. I power > the robostix and the wifi module separately since wireless requires > such a big current draw. For the curious, a diagram of the circuit is > here: > > http://kaju.dreamhosters.com/images/Images/powerdiagram.jpg > > I am attempting to use the same circuit to power the gumstix verdex > pro from the iRobot Create's battery. Please know that the verdex > pro works just great when plugged into the wall, but that doesn't make > for a cool autonomous robot. > > Initially, using the same circuit resulted in the verdex rebooting > itself again and again. I figured that the verdex has a greater > current draw than the connex, so I built some custom linux images > using BitBake. I'm using wireless (piggy!) so I can't turn that off. > In the custom linux image, I turned off bluetooth, hoping to gain > enough savings. Doing so allows the verdex to boot to the prompt and > run for about 3 minutes, but then just subsequently reboots. > > I feel stuck. Anybody out there have any tips? I'm open to running > the verdex pro using a separate battery pack, but I'd like to hear if > anyone has been successful with a particular set of batteries. > > Sincere regards, > > > Tanya L. Crenshaw > > > ------------------------------------------------------------------------------ > Sell apps to millions through the Intel(R) Atom(Tm) Developer Program > Be part of this innovative community and reach millions of netbook users > worldwide. Take advantage of special opportunities to increase revenue and > speed time-to-market. Join now, and jumpstart your future. > http://p.sf.net/sfu/intel-atom-d2d > _______________________________________________ > gumstix-users mailing list > gum...@li... > https://lists.sourceforge.net/lists/listinfo/gumstix-users > |
From: Ned F. <nfo...@wh...> - 2010-08-24 11:45:59
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On 08/23/2010 11:27 PM, Tanya L. Crenshaw wrote: > Currently, I am able to power the gumstix connex from the iRobot > Create's battery using a simple voltage step-down circuit. I power > the robostix and the wifi module separately since wireless requires > such a big current draw. For the curious, a diagram of the circuit is > here: > > http://kaju.dreamhosters.com/images/Images/powerdiagram.jpg > > I am attempting to use the same circuit to power the gumstix verdex > pro from the iRobot Create's battery. Please know that the verdex > pro works just great when plugged into the wall, but that doesn't make > for a cool autonomous robot. > > Initially, using the same circuit resulted in the verdex rebooting > itself again and again. I figured that the verdex has a greater > current draw than the connex, so I built some custom linux images > using BitBake. I'm using wireless (piggy!) so I can't turn that off. > In the custom linux image, I turned off bluetooth, hoping to gain > enough savings. Doing so allows the verdex to boot to the prompt and > run for about 3 minutes, but then just subsequently reboots. There is no reason why you should not be able to power the Gumstix processors from the iRobot, however, there are several possible problems with your present design. A linear regulator is an inefficient way to create 5V from 15V. The efficiency is 33% and the lost energy shows up as heat in the L7805. The efficiency is even worse considering that the Gumstix uses a linear regulator internally to make 3.3V from the 5V, putting the overall efficiency at 22%. I'm not sure what the total current draw of your Gumstix is (I suspect that you don't know either), but the Connex/Verdex require about 1Watt @ 3.3V or about 0.3A. I know that my Netstix draws about another 1.5W, but I don't know the draw of the Robostix or WiFi. If I assume *no* power for the Robostix, that still leaves (15V-5V)*0.3A = 3W in the L7805. That is not a trivial amount of power and will require a modest heat sink on the L7805. Assuming you are using the TO-220 package, the thermal resistance, without a heatsink, is 50degC/W, so the temperature rise will be 150C, which would require the ambient temperature to be 0C or less, not likely the case. From the description of the symptoms you are having, it sounds like the L7805 is going into thermal shutdown and turning off the the 5V power. Your project would be much better served with a switching regulator that creates 3.6V directly from the 15V battery. The efficiency of the regulator can be 80% or better, and by regulating directly to 3.6V, rather than 5V, you lose less energy in the Gumstix internal regulators (because those regulators in-line with the power supply, you can't feed the Gumstix 3.3V directly). Greater efficiency helps in two ways; it saves battery power, and it reduces the heat that you have to dissipate from the regulators. To design or choose a switching regulator, you need to know the peak current requirement of your system. I suggest that you measure that when operating the Gumstix system from a bench power supply. Temporarily, you should be able to continue by adding a (bigger) heatsink to the L7805's. -- Ned Forrester nfo...@wh... Oceanographic Systems Lab 508-289-2226 Office / 774-392-5352 Cell Applied Ocean Physics and Engineering Dept. Woods Hole Oceanographic Institution Woods Hole, MA 02543, USA http://www.whoi.edu/ http://www.whoi.edu/sbl/liteSite.do?litesiteid=7212 http://www.whoi.edu/hpb/Site.do?id=1532 |
From: Tanya L. C. <tan...@gm...> - 2010-09-15 21:53:32
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Dear Cole Christensen and Ned Forrester Thanks to you both for your recent reply to my query about powering the verdex pro from the iRobot Create battery. I finally got a chance to try your solutions and they are working swimmingly. My first forum post to gumstix-users and what a positive experience. Back to my rabbit hole. Many thanks! -- "Dr. T." Tanya L. Crenshaw Assistant Professor at the University of Portland Office: (503) 943-7687 |