Power for the cradle

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. NOTE: The following describes a modification of your Palm, possibly voiding your warranty!!! A second note: After starting that page, I discovered Bens Pilot Page (UPDATE: I can't find his page anymore). He described the same idea. What I don't like, is his way to contact the free pin. I believe, solder on the golden pads is a problem. I was searching for another solution and I think I found one. I also wanted to provide a bit more information on a safe way to supply the Palm and charging the batteries. . WARNING: The Palm IIIc cradle (color Palm) uses the same pin than the following modification to supply power to the inbuilt charger of the Palm IIIc. NEVER put a Palm that was modified according to the instructions below in a Palm IIIc cradle that's connected with its original Palm IIIc power supply. That wall brick is NO charger, it's just a power supply that would ruin your NiMHs with it's 1Amp output current!!! . UPDATE: I finally changed the numbering of the pins to the 'official' standard. To make it clear once again: The pins on the cradle are numbered 1-10 from left to right looking at the cradle as it stands on your desk. Looking at your face down Palm with the connector pointing towards you, the numbers run of course 1-10 from right to left then. .

..Modifying the Palm - Pilot 1000/5000, PalmPilot Personal and Professional

..Modifying the Palm - Palm III

..Modifying the cradle - old type

..Modifying the cradle - new type (Palm III)

..Using the Palm IIIc cradle

..The right charger

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. Modifying the Palm - Pilot 1000/5000, PalmPilot Personal and Professional . When you read my page 'Power for the Palm', you've probably noticed that I'm a fan of rechargeables. I don't want to say that 3COM/USR missed something, when they left out the possibility of an external power supply. After all the Palm's a real low power device and I guess most people can live quite good with batteries. But for rechargeables it would just be nice, if they could be charged remaining in the Palm. BTW, the dot 7 command proves, that Palm did at least think about rechargeables. The craddle on the other hand is the perfect charging station (I'd wish my mobil phone charger would provide such a nice physical support ...). So my first thought, after I started using NiMHs, was how to modify the system.  . Fortunately there's one pin at the serial connector, that's not in use. It's the only pin that has no visible lead into the Palm, I name it pin 9, left of it (assuming your unit is lying face down, the connector pointing towards you) is pin 10 which is ground. You need to make a connection between this pin 9 and the positive batterie terminal. Soldering on the golden pad is no good idea, cause with the proper temperature the solder will flow over the golden surface and spoil the pad. I took 'silver conductive paint' instead, to contact only the very top. I don't know where to buy that paint in the States, but stores for model-making or electronic suppliers are good addresses. Don't get me wrong, it's not any silver colored paint, that wouldn't work. It's a special, fast vaporizing fluid with disolved silver in it. After applying, it dries quickly and only a thin silver layer remains, that's an excellent conductor (BTW, years ago I repaired the heatable rear-window of my car with it. There was a little crack in that heatable serpentine lead and you can't solder it. I just painted a bit of that silver stuff over it and it works since then. Saved me alot of $$$).  . For best understanding, look at picture 1 of the modification: .

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Start with the little L-shape wire, and fix it with a *little* glue. Then fix the resistor at the one end of that wire, so you can solder it together later. The resistor is more a protection and a good support for the wire. The value can be anything around 10 ohm, though it shouldn't be too high. Intelligent chargers don't like that. Take care that the end of the wire that points towards the serial pads, ends behind the virtual line where the bottom of the case presses onto the board. So the wire disappears completely after the case is closed. Now to the tricky part. Use some tape to mask a thin path from the wire straight to pin 9 of the serial port, it look like picture2 then: .

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Make sure the edges are firmly pressed onto the board, so the paint can't reach under the tape. Then apply the paint *carefully* from the top of the serial pad to the wire. Take special care not to short the wire to the ground ferrit (J4). Wait a few minutes (or until the paint is dry) and remove the tape. You should now have a perfect connection from pad 9 to the resistor. From there, just run another short wire to the positive batterie terminal. When you did everything right, you should be able to measure the battery voltage between pin 10 (ground) and pin 9. That's it for the Palm. .

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. Modifying the Palm III . The modification of the new Palm III is even easier, since 3Com was kind enough to connect an empty lead to the unused pad. So please read the section of 'How to modify the old Palms' and then forget all about the messy part with the silver paint :). Instead look at the image below and locate lead on your board. Right below the yellow arrow on the image, the lead disappears to the other side of the board and there it ends with a little golden test pad. But unfortunately we can't use that to solder a wire, since it is the area where the key contact rubber is located. And that should lie absolutely flat - so *no solder* on that side! Instead, scratch off the solder stop mask at the marked position. Take care that you don't scratch off the solder stop from the GND-layer left and right of the lead. It helps to prevent shorts, later when you have to solder your wire! .

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The rest is easy. Solder a little wire, possibly parallel on the scratched spot. It's up to you, whether you want to add the 10 Ohm resistor or not. You could also solder the wire directly to the battery lead, but be aware, that an accidently short between pin 10 and 9 for example will vaporize the little piece of lead between your wire and pin 9, not to talk about other damages!! A 10 Ohm resistor won't harm and it'll limit the current to a non-dangerous value. I fixed the SMD resistor (size 1206) with a *tiny* drop of hot glue - it isolated and is removable. Finally solder the wire - either from the resistor or directly - to the positive battery terminal.  It's a good idea to run the wire in about a 5mm (1/5 inch) distance along the battery compartment (like on the image). Look where the case back presses on the board when the case is closed, then you know why. .

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For this reason, you also have to do an additional, little case modification. Below you see an image of the case back. The housing of the RS-232 cover spring presses directly on the board when the case is closed. So the wire would be squeezed and/or the case wouldn't close properly. Just take a sharp knife or a cutter and cut a little notch where it's marked on the image. When closing the case, try to take care that the wire is running through that notch. Done! .

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. Modifying the cradle - old type . Well, there's not much to say about the modification of the cradle. The hardest part is to 'open' the bottom part of the craddle where the wiring is hidden. I think the easiest way is just to 'slide' the little front cover downwards, parallel to that 45 degree angle the cradle has. You can take a little pliers and squeeze that plastic pegs that are located at the bottom of the cradle, left and right where the cable runs in, while you simultanious try to slide the cover off. Sorry, it's the best explanation I can give.  Basically I found several posibilities to add the needed supply wire. The first and easiest of course is, an additional, seperate wire. Then you either fix that wire with several pieces of tape along the existing hot-sync cable or you have always that wire in your way. I don't like that.  The second solution is already much better. Additionally to the 6 wires yellow, brown, blue, black, green and red that are in use, there are 3 more wires, white, gray and purple, running in the hot-sync cable. They are cut off with the outer isolation, but they can lengthen again with a piece of wire. Unfortunately they have no connection in the 9-pin SUB-D connector, but you can open the outer isolation carefully close to connector and reach them there. In any case, using these free wires saves you the clumsy extra wire running over your desktop.  The last solution is a bit tricky. The hot-sync cable uses in fact two ground wires. One, the shield of the cable, is not connected to any of the 9 pins in the SUB-D connector but to its metal parts (case). The logic ground (pin 5 of the SUB-D) is wired via the red line in the hot-sync cable. In the cradle, the two 'grounds' are connected via a 10nF capacitor. This is a very common method to have spikes grounded but still avoid gound loops. Unfortunately no PC part supplier, especially the case manufacturers, care about these clean design rules. The reality is, that protective ground (the case) and logic ground are always connected via some PC components, and as all have the same logic ground, one is enough to spoil the whole concept. So the clean design of 3COM/USR is a waste and we could use one of the wires. The advantage is, that both are connected at the 9-pin side, so we don't need to harm the cable. But we need an adapter, that connects all pins of a male and a female 9-pin SUB-D 1:1, except pin 5. The metal case of the male goes to pin 5 of the female and to an additional wire that is the negative supply from the charger. The now free pin 5 of the male is connected to the positive supply from the charger. In the cradle we change the red wire from pin 10 to pin 9 and solder the shield to pin 10. All clear? ATTENTION: This solution is dangerous when you forget to use the adapter! Then, the battery is shorted via the earlier descibed PC ground loop (Don't loan the modified craddle to your best friend ... :-)  )  You can choose your preferred solution. In the end you need two wires for the charger: a negative from pin 10 of the craddle and a positive from pin 9. .

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. Modifying the cradle - new type (Palm III) . Actually the modification of the new cradle is the same than for the old one, but easier. First thing is, the new cradle opens much easier. When you take out the one screw at the bottom, the cradle falls basically apart. Then, there is no nasty hot glue over the pins we need. Instead, there is a nice, free solder pad. So just add your two wires to pin 10 and 9 and close the cradle again, that's it! What's really nice about the new cradle, is the lot of space in the case. If I find the time, I will think about a really good charging electronic to fit there - the space is just too inviting ... :) .

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. Using the Palm IIIc cradle . If you can get a hold of a Palm IIIc cradle, you have the perfect cradle to use with a modified Palm III. On that cradle, pin 9 is already connected to the middle contact of the DC plug in the serial connector, GND is the outside ring of the DC plug. So all you have to do, is to connect your charger (NOT THE ORIGINAL PALM IIIc POWER SUPPLY!!) to that DC plug - done. .

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. The right charger . The easiest solution for sure would be, to buy a charger and connect it to our two new wires. The problem with that solution is the following: nearly all NiCad or NiMH chargers, no matter how 'intelligent' they are, work with a constant current. That means, there is any voltage across the terminals that's higher than the nominal battery voltage before the batteries are connected. That voltage 'breaks down' to the actual cell voltage when contact is made, because there is only this limited amount of current. Modern, sophisticated chargers are even worse for our aims, cause they no longer have to know how many cells you're charging to detect a battey-full condition (nowadays delta-peak detection is the most common technique). So they are likely to be able to charge more than 2 cells and for that they need at least a voltage that is higher than all the cells together have. Let's assume you have a charger for only 4 cells. It supplies at least around 8-12V (2V / cell) with maybe 50mA constant current for slow charging 500mAh batteries. If we'd use that charger with the Palm, everything would be fine as long as the batteries are installed and firmly connected. But if there would occur any failure - batteries not in, temporarely disconnected or defective - the unit would get the full voltage. It only needs 15-20 mA in idle mode, so the current limiter of the charger doesn't work. Poor Palm!! The Linear Technology data sheets talks about a maximum of 8V input for the used regulator, but I doubt that all parts of the Palm will survive that attack. So, the specs for the charger have to be more specific, including: Maximum charge voltage 3.5V (which is tight, but just enough for 2 cells) Switch to trickle-charge when batteries are full (so you can leave the Palm in the craddle 'forever') Charge independent full-detection (batteries don't have to be empty when re-charged) Supply enough current to serve as power supply for operating the Palm (good for developers :-)  ) To make a long story short, I don't have a solution yet. In the moment I'm using a left-over prototype of a very expensive charger I developed for an AV company for their camera batteries. All parameters can be set independently on that device. But I agree, that would be a bit of an overkill ...  I'm thinking about a simple solution and I'll post the schematics here, when I found one.

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. Last updated: March 23rd, 2000 Copyright © 1997-2000 by Peter Strobel, all rights reserved.