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  1.    #1  
    To preface: This all concerns chargers/power supplies sufficient to get a Touchstone working in a car. I’m not talking about car chargers simply plugged into the Pre itself.

    All starting from the wildly varied experiences with people trying to get a Touchstone working in their cars using every car charger that they could get their hands on, from this thread:
    http://forums.precentral.net/palm-pr...-adapters.html

    It seems like people are having good luck lately with the one of the official car chargers. To be honest, the talk is often short and unclear. I can’t tell which official charger people are having luck with. There seems to be three and I can’t keep straight which is working for more people or what. As I mentioned in another thread (http://forums.precentral.net/palm-pr...ml#post1757288 ), it started to seem like the many car Chargers either flatly don’t work with the Touchstone, or people were having the Pre do an on/off (charge/not-charge) dance when plugged into these miscellaneous car chargers. I’m no electrician but I like to think I know enough to be dangerous. I felt these problems were indicative of one basic thing….these car chargers, whether rated for 1 Amp or not, were generally insufficient to reliably power a Touchstone and the Pre. Some higher quality car chargers seem show otherwise, as they are likely actually putting out near 1 Amp reliably and consistently. I tried one that some were having luck with and I had no luck at all. At that point, I decided I’m not going to full around anymore. The Touchstone (TS) isn’t meant to be used in the car and I don’t think we’ll ever see a car charger specifically rated to support the TS. I chose to get a little more specific & robust with my solution. I also wanted a clean set-up without anything plugged into a cigarette lighter.

    Your car battery, and alternator when the car is running, is churning out DC current, somewhere in the 12V neighborhood. USB runs at 5V DC. Note that they’re both DC; both in the same family. Unlike the wall wart charger that came with the phone, that has to convert from AC to DC. What the car chargers are doing is simply to reduce the voltage to the USB standard. I believe the output amperage of these things isn’t necessarily dictated by the current needed by devices but rather by the readily available (i.e. cheap) circuits to perform the voltage step down from 12V to 5V.

    In order to provide good, reasonably clean, and sufficient current to the TS, I did some shopping around for a DC-DC converter. The one I found (see pic) is made by Mean Well. It accepts input in the 9.2-18V range, and outputs at 5V & 5A. This is a more robust solution than a car charger because it uses discrete input and output stages with good (safe, secure) switching circuitry. I found this new on ebay for $20.

    If you look at the attached picture of the converter with the connections visible, here are descriptions of the connections:

    “V ADJ” is a potentiometer, used to micro-adjust the output voltage. This is about the most complex part of the whole process. After you plug this into the car, you need to use a multimeter to measure voltage across the output + & - connectors and adjust the little plastic set screw until you meter the device to exactly 5V. When I plugged mine in, my car was putting out 12.48V and the output at first was 5.21V. A few small twists with a Philips screwdriver, and I left it at 5.01V.

    “-V, +V” This is the output side. Here, I actually bought a short male to female USB extension cable off of Monoprice.com and cut it in half. I kept the female half for connecting to this device. The cables are color coded red=positive, black=negative (white and green are for data). This way I can use any USB cable I want, and I can even use this to power other USB devices if needed.

    Middle ground. This is a ground connection that is grounded to the car chassis via an under dash bolt to the fire wall. Since the input stage ground is also sent to the chassis, I just used a small cable to jump to the input ground line.

    “+ - input” is the input power from the car. In order to keep the install clean, I used a add-a-circuit device (see pic of cables below) that can be picked up at local auto parts stores. This add-a-circuit takes the place of a fuse in your under dash fuse box. What it does is simply splits the hot wire into two separate lines. It sends one back into the fuse box to keep the existing circuit that you’re stealing from working. The second goes out of the add-a-circuit, through a second fuse (not ethe two fuses. One is the original fuse, the second is for the new circuit), over the red wire. This red wire becomes + for the input stage. As previously stated the – goes to a bolt on the fire wall.

    So I end up with this box attached to a flat spot under the dash, using some heavy duty double sided tape from the auto parts store. I have no exposed wires, except for small stubs of the aux-input for my stereo and about 3 inches of the USB cable attached to the TS.

    OK, with me so far? Everything wired up right? Check. Little green LED on converter lit up? Check. Voltage adjusted to 5V? check. Plug in TS…Put on Pre…..nothing. It didn’t work. Just…nothing.

    At this point, I let it sit for a week (actually, to be quite honest, I originally had a gutted USB cable attached to the converter then decided to go with the female USB plug instead. I had to wait a good week before I got it ordered and shipped). After getting the female USB wire hooked up, and let my wheels spin in my head for a week trying to figure out where the error is, I decided there was one quick thing that I could try. Short the data cables on the USB cable. Now, I just cannot find the post where someone described testing the wall wart and such and finding that the data cables were shorted together, which may be some sort of signal to the thing being charged to turn on. This worked and I’m very happy with a very clean, quiet, and safe solution.
    Attached Images Attached Images
  2. #2  
    Oh, and here's a post describing the shorting of pins:

    http://forums.precentral.net/palm-pr...tone-dock.html
  3. #3  
    So it would seem that your theory is that the problem with most of the car chargers going to the Touchstone (assuming current output is correct and the data pins are shorted) is improper voltage? If that's true, I wonder how sensitive the Touchstone is to voltage? Perhaps you could experiment by adjusting your set screw both above 5v and below by tenths of a volt and testing at each point.

    This also makes me wonder how stable the voltage on your car's electrical system is. Perhaps it's higher or lower in the summer? The voltage regulator is supposed to take care of it, but I have no idea how good it is at doing that.

    Need more testing!!
    Palm III-->Handspring Visor-->Sony Clie PEG-NR70-->no PDA -->Palm Treo 755p-->Palm Pre-->HP Veer
  4. #4  
    I know when I ran High Output Amps in my Trucks the voltage was all over the place just during normal driving. It was some years ago but I always ran a high Capacity capacitor to help stabilize this. I had meters on both sides to monitor this back then on Both batteries ( main truck and System dedicated).

    When you start out with 12V there just isn't a lot of room for variance when stepping it down. you have a good solution wit that but i also wonder how stable it will be .

    I have an OEM AC charger in my Jeep (it has built in inverter) and the newer Palm DC one in my Company Van and to use in my Older Jeep. They have been working great so far with the Touchstone with no resets or having to have the Pre turned off during mount.

    I'm also wondering how many are just having touchstone issues as they seem to be reported more and more now .
  5.    #5  
    I don't think it's voltage. I think its current/amps. For the few people who can't seem to get anything working, it might very well be a voltage issue with their specific car. But I think that has to be rare. With that in mind, I'd rather be able to test this thing by varying the current! It might be very telling if I could step the current down in steps between 1.5A and 500mA, and see what the TS & Pre does along the way. With varying the voltage, think we might run the risk of damage first before actually replicating the common problems (on/off dancing) that I think we sooner see by varying the current.

    Thanks for finding the link, Keegan99. That's the post I was looking for but none of my searches were working.

    I too was using an inverter before this also. It worked fine but was a real sloppy set-up in my vehicle.

    I will say this though. Some of these ultra cheap cig lighter charges just might work if you could short out the data ports. Unfortunately, those things don't typically have any wires hooked up to the data ports on the USB output to cross.
  6. #6  
    I ordered the Meanwell SD-15A-5 today. It's a considerably smaller form factor than the SD-25A-5 which the original poster used. It measures just over 3" x 2" x 1", but can still deliver 3A, more than enough for the Touchstone.

    However, every place I called had a minimum order of $35 - $50, so I had to get two. If you'd like my extra for cost (~$25) + shipping, just send me a PM and we'll make it happen.

    The datasheet is here:

    http://www.cdiweb.com/datasheets/mea...SD-15-spec.pdf
  7. #7  
    I kind of like this idea, and it does not seem to be too intrusive to the vehicle.

    What I do wonder, though, is how it handles power dips. Some people, myself included, are noticing that when power operated features of the vehicle (turn signals, brake signals, etc.) cause the power to dip momentarily, resulting in it seeming like the device was taken off of the touchstone.

    I would assume that this has a capacitor to prevent that.
    Did you know:

    webOS ran on a Treo 800 during initial development.
  8.    #8  
    nice find, Keegan99. Let me know how it goes.

    dkirker, I'm not sure what you mean by losing power. A dip in watts? These things are churning out 4x or more than the TS/Pre need. A dip in voltage? The switching power supply circuitry isn't going to let voltage stray too far. Amperage? moot point like Watts. There is more than enough on tap for TS/Pre. What you're describing on the car chargers is different because those devices are walking a fine line of providing enough current to the TS/Pre to begin with (not even to mention that there might be some sort of noise effect through the cheap circuitry).
  9. #9  
    Quote Originally Posted by Nurgling View Post
    dkirker, I'm not sure what you mean by losing power. A dip in watts? These things are churning out 4x or more than the TS/Pre need. A dip in voltage? The switching power supply circuitry isn't going to let voltage stray too far. Amperage? moot point like Watts. There is more than enough on tap for TS/Pre. What you're describing on the car chargers is different because those devices are walking a fine line of providing enough current to the TS/Pre to begin with (not even to mention that there might be some sort of noise effect through the cheap circuitry).
    I'm using the term "power" loosely since I have not tested to see if it is a voltage or a current drop. I would believe voltage.

    I would assume that the device by Mean Well would have a capacitor to keep the voltage to the device (and current if it were to drop somehow) consistent. That's kind of what I was checking for.

    That, and if the Mean Well device draws any electricity when the vehicle is off. But, like I said, it could probably easily be wired to the same general circuit as the car stereo. That way it would only operate when power is applied to the stereo.

    Looks like a project that is worth it.

    I was using the Palm car charger meant for the Pre, before I was using a power inverter.
    Did you know:

    webOS ran on a Treo 800 during initial development.
  10. #10  
    And it looks like another trip to Fry's is in the works: FRYS.com*|*Transformers

    EDIT: I guess not. Appears that I confused the model #s... That seems to be the AC/DC model.
    Last edited by dkirker; 08/06/2009 at 12:26 AM.
    Did you know:

    webOS ran on a Treo 800 during initial development.
  11.    #11  
    Quote Originally Posted by dkirker View Post
    I'm using the term "power" loosely since I have not tested to see if it is a voltage or a current drop. I would believe voltage.

    I would assume that the device by Mean Well would have a capacitor to keep the voltage to the device (and current if it were to drop somehow) consistent. That's kind of what I was checking for.
    Ok. Voltage may very well be controlled via cap and IC. Personally, it doesn't matter since we're not building the thing (power supply design is truly an art form and not for nubs like us). What we know here is that these are rated at 2% line regulation and 2% load regulation. Which means the output voltage (and current) is only going to change at a rate of 2% of the change at the input side. Let's say input voltage spikes to 18V? 2% of 6V is +0.12V? (I'm really not sure why you're going down this voltage path. Are you coming from a car stereo beckground and are used to the noise and power supply problems over there or something?)

    Anyway, that's just part of the benefits of a good switching power supply vs. a linear voltage regulator like the cheapy cig lighter jobs. We're getting discrete/isolated input and output stages, short circuit protection, overload protection, over voltage protection (and in my case an separate fuse just for this device in advance (i.e. easier to replace without having to disassemble the PSU) of the internal fuse.

    Now, I'm not sitting here trying to sell everyone on this set-up. I personally think it's actually the safest way to go, if you know how to hook it up. But it's not for everyone, I'm sure.

    That, and if the Mean Well device draws any electricity when the vehicle is off. But, like I said, it could probably easily be wired to the same general circuit as the car stereo. That way it would only operate when power is applied to the stereo.
    Well, this has everything to do with where you plug it in and not the device itself, now doesn't it? I would have loved to have just tapped into an otherwise meaningless circuit off of the fuse box, like the dome light circuit, but that is always on. If you use the add-a-circuit, like I did, you'll need to find one, perhaps via trial and error, that is switched. If you plan on tapping into some other wired power source (like the leads to the cig lighter or the stereo), that's a different story (those two anyways are switched).

    I was using the Palm car charger meant for the Pre, before I was using a power inverter.
    Yeah, I was on an inverter too before going this route. I have a nice 350W one but it has a fan is noticeably loud. I'm glad to be rid of it.
    Last edited by Nurgling; 08/06/2009 at 06:41 AM.
  12. #12  
    Quote Originally Posted by Nurgling View Post
    Ok. Voltage may very well be controlled via cap and IC. Personally, it doesn't matter since we're not building the thing (power supply design is truly an art form and not for nubs like us). What we know here is that these are rated at 2% line regulation and 2% load regulation. Which means the output voltage (and current) is only going to change at a rate of 2% of the change at the input side. Let's say input voltage spikes to 18V? 2% of 6V is +0.12V? (I'm really not sure why you're going down this voltage path. Are you coming from a car stereo beckground and are used to the noise and power supply problems over there or something?)
    Nope. I actually have no electrical background. I'm all software.

    I've thrown a decent amount of money trying to engineering a setup that is clean and works. I'm supposed to be saving money for college, and I've found that I've spent quite a bit more than I should have on this project. So I want the next solution to work, especially if I am digging under the dash. I'd hate to slap down money only to find that I get the same effect as I do with the cig lighter.

    Quote Originally Posted by Nurgling View Post
    Anyway, that's just part of the benefits of a good switching power supply vs. a linear voltage regulator like the cheapy cig lighter jobs. We're getting discrete/isolated input and output stages, short circuit protection, overload protection, over voltage protection (and in my case an separate fuse just for this device in advance (i.e. easier to replace without having to disassemble the PSU) of the internal fuse.
    I figured that this power supply would provide what I expect it would, but I wanted to make sure that you didn't have any bad experiences with it.

    Quote Originally Posted by Nurgling View Post
    Well, this has everything to do with where you plug it in and not the device itself, now doesn't it? I would have loved to have just tapped into an otherwise meaningless circuit off of the fuse box, like the dome light circuit, but that is always on. If you use the add-a-circuit, like I did, you'll need to find one, perhaps via trial and error, that is switched. If you plan on tapping into some other wired power source (like the leads to the cig lighter or the stereo), that's a different story (those two anyways are switched).
    That's as much as I figured. Though, not being an electrical engineer or an auto mechanic (and I've only owned the Chevy for a year, and have not actually done any custom work on it), I wanted to make sure that my suspicions were confirmed (going back to the "money" thing).

    It seems logical that the switch (or lack of switch) would go before the fuse box, but, I've seen people do illogical things on big products before...

    I'll probably tap into the powered window system or the stereo. Though, the cigarette lighter is NOT switched in the '97 Astro. That's always on.

    Quote Originally Posted by Nurgling View Post
    Yeah, I was on an inverter too before going this route. I have a nice 350W one but it has a fan is noticeably loud. I'm glad to be rid of it.
    Mine doesn't have a fan (it is a Targus model), but it is pretty big. I can store it in a little storage pouch on the passenger side of the dash, but I still have to plug it in when I get in the car. I can then use the inverter for other tasks, after this mod.

    I'm actually thinking about wiring the setup so that the female end of the USB port going into the PSU is exposed in the back of a small cove in the dash so that it can be used for other devices requiring 5v 1a-3a. Then I can hide the cable going to the Touchstone, except for the connection between the cables. (It is a bit hard to explain without showing. I'll take pictures when it is set up.)
    Did you know:

    webOS ran on a Treo 800 during initial development.
  13. #13  
    If you plan on tapping into some other wired power source (like the leads to the cig lighter or the stereo), that's a different story (those two anyways are switched).
    This varies by make and model... and probably even year. My '01 Explorer always leaves the cigarette lighters on, though I think such unswitched lighters are solidly in the minority.


    In any case, I'm anxious to get my Meanwell and try it out!
  14. shoolace's Avatar
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    #14  
    @Nurgling - Agree with you on the simpler DC-2-DC solution. Received my package today and completed my install. Worked perfectly in my car. Thanks for the tip.
  15. #15  
    Thanks for the information Nurgling. I'm going to hook up my system like you described.

    Quick question... with the add-a-circuit what is the minimum fuse that the SD-25A-5 converter needs? In you picture I think I see a 10 amp fuse??

    I'm thinking of using the radio fuse for the add-a-circuit and mine is a 10 amp. I just want to be sure I have a large enough fuse for the converter. You can probably mix different size fuses with the add-a-fuse also couldn't you? In other words take a 10 amp out of the fusebox, replace the 10 with the add-a-fuse, put the 10 on one side of the add-a-fuse and whatever the converter needs on the other side...

    Thanks!!
  16. #16  
    Just wanted to let you guys know that the mp3car.com site has a few DC-DC options in their store. I'd bet they're not the dirt cheapest, but you shouldn't have to deal with minimum order amounts that electronics houses typically like to impose. Just fish over to store -> power and check them out. I liked this one in particular, it's small and could be easily mounted under dash: DCL11 Automotive Point-Of-Load DC-DC 15W Power Supply

    note: I'm not a shill, just have found that site to be very helpful in the past. I'm sure if any of you tinkerers get into it, there's more info on car integration, etc. that may be useful for the pre.
  17. #17  
    Hey guys - thoughts on LM317 Variable Power Supply ??

    I'm handy with a soldering iron and it's cheaper than anything else i see out there...
  18. #18  
    Quote Originally Posted by jbg7474 View Post
    This also makes me wonder how stable the voltage on your car's electrical system is. Perhaps it's higher or lower in the summer? The voltage regulator is supposed to take care of it, but I have no idea how good it is at doing that.
    The regulator is set to provide a decent charge voltage for a 12V lead acid battery, i.e. something greater than 12V. A typical automotive electrical system is 13.5-14.5V when the engine is running, 12V-12.6V when it's not depending on battery health. The regulator only takes care of the output from the alternator; it cannot do anything to stabilize the system at large from fast transients when inductive loads, like any of the million relays in a typical modern car, are switched on or off.

    Here's a fun quote from the data sheet for Linear Technology's LTC3728L DC-DC switcher IC:

    Automotive Considerations: Plugging into the Cigarette Lighter

    As battery-powered devices go mobile, there is a natural interest in plugging into the cigarette lighter in order to conserve or even recharge battery packs during operation. But before you connect, be advised: you are plugging into the supply from hell. The main power line in an automobile is the source of a number of nasty potential transients, including load-dump, reverse-battery and double-battery.

    Load-dump is the result of a loose battery cable. When the cable breaks connection, the field collapse in the alternator can cause a positive spike as high as 60V which takes several hundred milliseconds to decay. Reverse-battery is just what it says, while double-battery is a consequence of tow truck operators finding that a 24V jump start cranks cold engines faster than 12V.
    Yeah, uhh... it's Kevin. (KevinT was already taken.)

    PalmPilot Professional, Palm V, Kyocera 7135, Treo 600, Treo 650, Treo 700p, Palm Prē & Prē 2, HP TouchPad & Veer
  19. #19  
    Quote Originally Posted by Phenoum View Post
    Hey guys - thoughts on LM317 Variable Power Supply ??

    I'm handy with a soldering iron and it's cheaper than anything else i see out there...
    It can be darned cheap but you'll likely fry it. The LM317 is a linear regulator, i.e. uses a series pass transistor to act like a big resistor to drop the precise amount of voltage required to net you 5V at the output. The problem with that is ohms law, the power dissipation on 'the big resistor' equals current * voltage, so dropping 13.8V to 5V at 1A means that the poor little LM317 is putting out 8.8W of heat! The silicon will do 2A, but not if the voltage drop is high enough to burn it up before it gets there...

    Even being aware of all this, I tried it myself a few weeks ago with the similar L7805CT regulator in the beefier TO-3 case bolted to the metal cage around my car stereo (conveniently the metal case is the regulator's ground terminal), figuring that would be a big enough heat sink for those 9W. No go, but I didn't know that I needed to short the white and green wires in the USB cable when I did it...

    I should give it another go but have had second thoughts about how hot it'll get even bolted up to that metal cage, so found this thread in my search for a decent DC-DC switcher for Touchstone use.
    Last edited by ktessner; 10/28/2009 at 06:12 PM.
    Yeah, uhh... it's Kevin. (KevinT was already taken.)

    PalmPilot Professional, Palm V, Kyocera 7135, Treo 600, Treo 650, Treo 700p, Palm Prē & Prē 2, HP TouchPad & Veer
  20. gpgyo's Avatar
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    #20  
    Sorry to revive an old post but considering the popularity of the thread where people are posting pictures of TS mounted in cars (linked in the first post,) there's apparently a lot of interest in this area and what's discussed here seems to be the best route.

    I've read what's here and done some shopping around. For those interested, the Mean Well SD-25A-5 Nurgling used can be had at Fry's for $33. If you have one in your area and are too impatient to wait for delivery, that's an option. Since that model is overkill for this application, Keegan99 mentioned he used the Mean Well SD-15A-5. Jameco Electronics in California sells that model for $20 + $6 shipping (or you can pick it up if you live near them.) If you order online, there is no minimum order size. (Keegan99, if you haven't sold your extra, I'm going to feel like a jerk for posting this.)

    Now all I have to do is wait for all the pieces to arrive and find a place to mount a TS is a most un-TS-friendly A4!
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