Alberto Varela Dec. 14, 1998.-
I recharged the pair of batteries outside of the Palm with an inexpensive loader, to an approximate rate of 1/ 10 of the capacity (in mA). It is possible that it don´t obtain 1000 cycles of load-discharge without a professional loader (as the maker says), but something as well as 700 cycles still are good for me. This is the equivalent of using 350 pair of Alkaline (they have the double of energy). In the local market (Argentina) they represent about $ 320, and two Ni-Mh costs $16 (Maximum). It even could be less than 700 cycles, the point of crossing is approximately 18. (1 Ni-Mh costs the same as 8 alkaline, therefore who it want to could take out the bill. It doesn't have importance, it is purely speculativ).
I also wanted to avoid opening the door and the substitution of the batteries of the Palm with each discharge.
This happens the double of times with Ni-Mh because their energy, in AAA size, it is approximately the half in comparison with the Alkalines (550 mA/ h* 1.2 V= 660 mW/h against 850 mA/ h* 1.5 V= 1275 mW/h, respectively). ( With Ni-Cad it is worse: 220 mA/ h* 1,2 V= 264 mW/ h ! ).
The logical solution is to recharge the Ni-Mh batteries in the same Palm!
My
modification of circuit is in order to load, or help to the load, maintaining
lower the discharge of the two Ni-Mh piles that I use:
After installing the Hot Sync for port series in the PC, two of the paws of the connector DE-9 of that port keeps high tension (they are the DTR exits and RTS- the other exit, TxD, has negative tension).
The specification RS-232 says that the signals between +3 V and +15 V corresponds with logical zeros and its negatives values gives logical ones.
It is also recommended in the original specification that the maximum current is 500 mA (in the PC all the manufacturers limit it in much less: about 10 mA).
One could generate a simple equivalent model of Continuous Current of the exit of the port series RS-232, based on a voltage source and a resistance in series. The voltage is measured in open-loop, and by means of the reading of current in short-circuit to ground the value of the resistance is determined (applying Ohm´s law: R= V/ I).
I made mensurations in a few PCs that had at hand and I could take out the following conclusions:
The outputs RS232 of desktop PCs (TxD, DTR and RTS) correspond to voltages of around +12 V (or minus 12 V) with a resistance series of 1200 ohms. (There could be variations, although generally happens is that the current in short-circuit is about 10 mA).
The same outputs in Notebooks are generated for voltages of order of the 6/ 8 V, also limited in current to about 10 mA . (How interesting fact, the Palm Pilot generates them with 3.3 V and 330 ohm in series, also limiting in 10 mA).
The mensurations made by me are in the ANNEX, where I also calculate the power given by each outputs as a comparative fact between different makers.
I thought of taking advantage of these small currents in order to recharge the batteries and I put it into practice, with positive results.
With the use of three of small silicon signal diodes 14 mA of load is gotten approximately (it could be something more or less according to the PC), when the Palm is connected to the PC (Palm in the Cradle and ON PC, of course).
The Figure 1 shows the circuit. To the left: C.C. Equivalent Model of the PC Serial Port. In the center the Cradle with its connectors. To the right the Professional Palm Pilot with its connector of 10 contacts.
A diode (D2 in the figure 1) is in the Palm. The other diodes (D1 D3) are in the Cradle.
The figure 1 show that by means of D1 D2 the current of load comes from the paw 7 of the serial output connector of the PC, and he is approximately 7 mA.
In the same figure 1 the diode D3 will give about 7 mA more , taking advantage of the free cable between paw 6 of the DB9 and paw 10 of the Cradle. This cable was disconnected by me (marked with a X in Fig 1) because I added the suppression of the DTR line of the Palm, stopping the unnecessary drainage of the battery.(http://www.conklinsystems.com/pilot/drainfix.shtml)
In order to add those other 7 mA it is necessary to make an adapter with two DB9 Connectors (male and female) that I tie a to a the whole paws, except: pin 4 (female) connected to the 6 (Male). (In fact its not necessary connect the pins 1 to each other 1 neither 9 with 9).
I found comfortable making the
crossing of line 6 to the line 4 using a small piece of Cooper Clad
(material used for printed circuits) in order to link the connectors male
and female DB 9, separating the areas of cooper with small incisions in
the surface, by way of printed circuit. It shows in the figure 3.
In
the ANNEX I calculated the values of current
of load that one could expect in the different PC in which I could make
mensurations. I took 1.2 V per cell as normal value of voltage of Batteries,
although it could be something higher or lower, according to the level
of load.
I (mA)= (Vb-3.8)* Icc/ Vb (Vb in Volt; Icc in mA; 3.8 comes from adding the voltage of the two Ni-Mh Batteries- 1.2 v each a- plus two barrier of Silicon diodes - .7 V each-)
Example: With Vb= 12 V and with Icc= 10 [mA]--------> I= 6,833 [mA].
Of course, the values of current load are duplicated if two outpus are used, as it was explained above.
I don't truly believe that this minimum load (7 or 14 mA) could occasion problems because it is necessary to apply it for 100 hours, or more, (50 h. to 14 mA) for a complete load, assuming zero use of the Palm.
This
modification didn't have bad effects in the communication series
(proven only in Local Sync since I don't make use of the Palm Modem, although
it should do no harm).
The mentioned loader could be easily implemented with a mere source of tension (DC) of low price, of those that they are used for small apparatuses. Their tension could be of 6 V to 12 V, with the attaché of a resistance for current limiting. The resistance will vary between 75 to 150 ohms (1/ 2 W) according to the tension of the source, assuring about 35 to 55 mA of loading current.
The connection of the current of load could be made in several places: One of them is directly in the Palm, by means of the attaché of a connector like the apparatuses with external feeding.
Another capable place for the connection of the external source is in the modified Cradle, with the attaché of a silicon diode in series (D4). The connection of that diode D4 should be made in the Cradle in the union of the D1and D3 diodes. (See Figure 1).
And
finally my elected form, the simplest, that is by means of the DB
connector 9 of the cable of the Cradle using a DB connector 9 male with
their paw 5 for the negative and their paw 7 to the resistance of current
limiter of load (see Figure 4).
What
is the utility of this circuit? Taking advantage of the night for
a complete load, or use it in case of going on vacation, far from the PC
(taking the Cradle and the source). Remember that the key idea of these
modifications is not needing to retire the piles of the Palm in order to
make them a recharge. (And also show to our friends how the curve of the
tension of the batteries stay constant, as theirs "always" descends).
Of course you should control the level of load of the battery since there is no "intelligence" in this loader. The Palm possesses indicators from the state of tension of the piles and there are Freeware programs that give precise digital instruction and included graficals in function of the time of use.
When do you have to suspend the load? Well, according to some mensurations that I made, is quite good indicator the mensuration of 2.80 V.
NOTES about the practical aspects of the modifications:
First: you should keep in mind that any made modification could give rise to the cancellation of the guarantee.
Second: you should remember that
the Pilot is a marvel product of the [miniaturización], so
everything in it is small and the operations should be made with supreme
care and be planned previously.
If it is possible take advantage of the experience of
another, it is better that make it for one self. I recommend checking
the Web seeing other
pages with internal photos so much of the Palm like of the Cradle,
with careful instruction of dismantling and armed.
Third: Any modification that is made is at risk of the interested, not being the author of this page responsible for damages that they could happen.
Fourth: I recommend make Backup of the data, I don't sole by facing a modification, but like line of conduct mature in computer science. This is recognize you a serious estatus to this machine, leaving aside the concept of toy.
Fifth: Although the shown modifications are extremely simple for an Electronic Engineer (my case), it is possible that they represent any level of complexity for a neophyte. It is important to understand well this topic and if this is adapted to the particular use you give the Palm.
Sixth: The whole experience that I have is in my machine, a Palm Pilot Professional with 1 Mb memmory. Therefore the shown modification could not be valid in other models, and it even could generate damages or interruptions of operation. I don't know it with accuracy, but I believe that the idea is valid in general lines in all the Palms.
If I in any moment mentioned registered marks I didn't make it with the spirit of opening judgement of value of no type neither I try to use them in my favor or discredit them and if in any case any maker understands that I would owe their reference, I agree in making that of immediate and request the excuses of the case if it is necessary.
About 3Com and USR, makers of Palm
Pilot, I only have left to express them my gratefulness for the development
and the production of this product, without this or another modification
faced by my means a diminution to the magnificent design of the same.
With regard to the copyrights for this work, I give the same to any that makes the modification or uses this idea, whenever in character not profitable, for their own use and without spirit of lucre. He is not so in case of industrial production or use with economic inducements. In this last case I suggest contact with me to the effects of arriving to agreements on transfer of rights.
I have used information of the page of Ron Nicholson for this modification in the corresponding to the diagram of paws of the Cradle and of the page of Pedro U. Strobel (Peter´s Pilot Page) in what it makes to the characteristics of the Batteries and the care in operating with the open machine.
I believe that the Peter's Pilot Page is one of the most technically interesting on Palm Pilot of the Web. You can´t miss his notes about Rechargeables.
The Page
of Luiz Coutinho is of obliged visit in order to understand the operation
of the Pilot. It has very good photos and diagrams.
If you find this modification of utility or you have any comment please don't hesitate to send me a Mail:
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