Introduction
This project is my solution to what many Psion users find very frustrating: having to replace
the AA batteries with new ones or rechargable ones, sometimes very often!. It can be very annoying because if you
are buying normal batteries, then it can cost you allot of money each time the old ones go low on power. Or if you
are using rechargable ones, you need to take them out and replace them with others while you recharge (and maybe
pre-discharge as well) the set that has gone flat over time. The process can be long and you also need to take out
the AA battery charger unit each time you need to do this, or carry lots of extra batteries with you. Shouldnt there
be an easier way? Well with the Psion Revo, they added a rechargable battery pack internally which you never had
to worry about, so that fixed allot of hassle if you have a Revo that is. So what about the Psion 5MX? can we do
the same thing as the Revo with a simple plug and recharge option? Well thats what I asked myself recently and
decided that us Psion 5MX owners should have the same benefit as the Revo owners! This web page is about my
experience and advice if you wish to add the automatic recharge option to your Psion as well. Also it always helps to
read a HOW-TO page from someone who has already done what you want to do, there is no need for you to design your own
when there is a perfectly working design and model to copy. In this document I will explain...
- How the recharge circuit works
- How to build the recharge circuit
- How to test it before installing it
- How to install it inside your Psion 5MX
- Any other issues you should be aware of
** WARNING ** - MAKE SURE YOU READ THIS!
I recommend that you should be experienced with electronic projects before you even think about attempting
this project, for one your Psion is a complex and expensive piece of equipment that no doubt you value highly. If you
do not know much about electronics or have little experience then your project could easily fail as a result of this.
You could seek the experience of someone else instead of wait until you have enough experience using electronics,
handling power and electronics and soldering. I strongly advise that you use anti-static precautions when
handling the Psion internal motherboard and all other electronic components, voltage spikes could render this
equipment useless if you do not use the proper equipment to protect the very sensitive electronic circuits.
I also recommend that you are skilled enough to use a soldering iron properly. If you choose to undertake this
project yourself, I will not be responsible for any mistakes you do or errors you made, it is at your own
risk that you undertake to perform this project!
Tools you will need
- A good soldering iron with fine tip
- A solder sucker (if you make soldering mistakes)
- Fine solder
- A small cross (X) head screwdriver
- A multimeter with conductivity, resistance, current and voltage testing
- Wire strippers
- Paper/pen (to write down notes etc)
- A lighter (to shrink heatshrink tubing)
- A anti-static wrist band connected to a 1 Meg Ohm resistor which is earthed properly
- Some plastic tape or masking tape
- A power adapter set at approximately 6V DC (regulated) providing 100mA (min)
- A razor craft knife
Before you begin - VERY VERY VERY important!
Make sure you backup ALL of your data on your C: drive to your computer using PsiWin or copy it to a
compact flash card in D: drive. To perform this project you will be required to completely reset your Psion 5MX, this
mean the 16MB RAM memory (Drive C:) will be completely erased. All of your documents, applications and system
settings need to be backed up so after you have completed the project, you can restore drive C: back to its original
state. This is a required step because no battery or backup battery will be kept on the Psion while it is taken
apart and the circuit added. Thus without battery or backup battery power, the memory (drive C:) will be lost. If
you do have a compact flash card in drive D: do not worry, the content of the compact flash card will not be lost.
For fast restoration you could copy everything on drive C: to a folder on drive D: (compact flash card) if you have
enough space so the restoration process can be very quick and without having to connect to a PC and do a system
backup using PsiWin and a serial or IrDA cable. Simply copy everything back from the place you copied on drive D:
to replace everything on the reset drive C: after the Psion is assembled again. If you have plenty of junk on your
C: drive and its a complete mess, you could save everything you need and simply not do a backup and start your C: drive
from scratch again. (Kind of like reinstalling Windows ;)
Some background on this project
Yes this project does infact work, I have completed it myself within one day and fully tested the
circuit as well as the recharging process of the circuit. My modified Psion now functions normally and has the
added benefit of the automatic recharge functionality so I do not have to face the hassle of each time having to
remove the batteries and install/recharge new ones. I have used two POWERhaus (China) 1.25V AA 1300mAh batteries
in my Psion as my choice of rechargable batteries which seem to work fine.
Circuit theory
Basicly this circuit is very simple and does not require allot of complex or expensive electronic
components so it is very inexpensive money wise to implement. The external power supply which can be connected
to the Psion is a 6V DC (regulated) supply which when used sources all of the Psions power requirements and stops
any power drain from either the AA batteries or the backup battery. To recharge the Psion's batteries you MUST
use rechargable batteries and NOT the normal batteries, if you use normal batteries you risk them heating,
leaking or exploding and thus turning you must loved Psion into a pile of melted plastic. The choice of NiCad or
Ni-MH type (or other) type of battery does not matter as long as they are regular sized AA batteries with a given
voltage specification of 1.2V to 1.5V and a milliamp/hour rating of as high as you like/can afford. Obviously the
higher than mAh rating the longer the batteries are going to last in your Psion and the longer they are going to
take to fully trickle charge.
We are going to use a simple trickle (low current) charging method which does not monitor the charging process.
The reason why we do not need to monitor it is because unless other charging methods which charge very quickly,
ours only charges at a very slow rate. Our batteries thus will not experience the kind of stress like conventional
battery rechargers use that charge in a short time by using large amounts of current. When using a small charge
current we can use a constant charging method which should not do much damage to the battery cells over a long
period of time.
To charge rechargable batteries you need to introduce a voltage slightly larger than the desire charged voltage.
The larger charging voltage produced current flow to the battery cell charging up the store voltage and current
to the source voltage level. To do this using the Psion, the batteries we use are either normal batteries
giving 1.5V each (3V total) or rechargable batteries which are rated normally at 1.2V (2.4V) or 1.25V (2.50V).
The Psion is usually pretty happy to operating from approximately 2.2V to 3V and even slightly more than 3V
for normal batteries which come at 1.7V some 0.2V above the normal packaging rating of 1.5V.
To charge our rechargable batteries we are going to charge up to approximately 3.3v for any two AA batteries
which will be rated from 2.4V (1.2V each) to 3V (1.5V each). We are going to consider that we can buy 1.5V
AA cells so we need to use a voltage slightly higher than 3V, thus 3.3V should be ok. As I have said before,
the Psion can happily use a battery source deliverying from 3V to 3.4V (and maybe slightly more?) so charging
our batteries up to 3.3V to 3.4V should not do any damage to the circuit which the batteries will feed to
allow our Psion to operate normally. Even if our batteries are both rated at 2.4V together we can usually
safely charge them up more than this anyway without any bad effects. Charging them up to a higher voltage
however is really not recommended at all so we will keep to 3.3 to 3.4v maximum.
To charge we are going to use the 6V source input from the external power adapter, but we must drop this
voltage to our 3.3V/3.4V desired level to do the actual charging. To do this we use 5 small signal diodes
to drop the input voltage down to the desired voltage and then feed this into the positive terminal of
the battery pack in the Psion. Each diode will drop the voltage approximately 0.78 volts, linked in
series with 5 diodes will produce 3.9V across the circuit. The extra 0.78 volts dropped comes from the
reverse current protection diode used to stop any current flowing back into the recharge circuit. We only want
current to flow into the batteries and not backwards. This also insures that no power is lost in theory back
into the recharge circuit when the external power is disconnected and the batteries take over the task of
providing the power supply to use the Psion as normal. Therefore our reverse protection diode serves two
roles, to stop current from flowing from the batteries into the recharge circuit (and possibly to the external
power socket) and also to stop any power leaking when the batteries are being used as the sole source of power
for the Psion ensuring the battery life is the longest possible.
The resistor allows us to control the amount of current we are going to use to charge the two AA batteries with.
I recommend using a 1/4 watt 220 Ohm resistor, this will produce 27mA current supply for the two cells.
It also results in a maximum supply power rating of 180mW which is under the power rating of 250mW of the 1/4
watt resistor. It is best not to use the full power rating of the resistor otherwise the resistor could start
to produce heat and heat is no good for any circuits, especially inside our Psion. Using a lower Ohm resistor
is possible to make the charging process faster but not recommended by myself. During the charging process
the power consumption by our recharge circuit will reduce over time as the battery cells reach their desired
charge stored voltage and current levels. Using 1300mAh battery cells as I do will require approximately
48+ hours for a total recharge using our low current trickle charge circuit. Because the power requirements of
this circuit as so low and the recharge current feed into the battery cells is low the risk of overheating of
the battery cells and overheating of the Psion plastic casing is very low. The goal is not to produce a Psion
which can be quickly recharged, but a Psion which can be left on a external DC adapter and slowly and constantly
charge even over a long period of time when not in use. Because the Psion will not use much power during the
day of use, the recharging requirements will also be typically low during the connection to the external power
adapter during the time it is not being used or at night time. The Psion can be plugged into the adapter and
'topped up' to full charge in a short space of time as most often we do not need to fully recharge the batteries
from little use. If you do however use the Psion and drain allot of power from it, and require the power to be
restored in a short space of time, you can remove the batteries from the Psion and place them into a conventional
battery charger for a quick charge if required, and then replace them back into the Psion. However it would
defeat the purpose of not having to remove the batteries at all by using the recharger circuit in the first place.
It may take time for your batteries to fully recharge if they are new and fully discharged. You could put the
Psion on the external power adapter for the period of time required to fully charge the cells or you could place
the cells in a normal recharger to charge them up for the first time using a quick charge. After that the
recharger circuit should be able to keep the cells 'topped up' with normal daily or weekly use.
Circuit diagram
Below we have the circuit diagram for the Psion 5MX automatic recharger:
Make sure you use a 1/4 watt resistor and the 1N4148 diodes, as these are small components and required to
make the circuit as thin as possible, using larger diodes or resistors makes the circuit height too tall
because of the added thickness of the components. The charge current is small enough so larger diodes and
resistor is not required anyway. The circuit needs to be as thin as possible to fit inside the Psion
and not raise the motherboard enough up in height. Otherwise everything will not fit together again.
The circuit has an added benefit of voltage tolerance, if external power supply voltage is not exactly 6V but
slightly lower or higher the charging voltage will still remain around 3.3 to 3.4 volts. While testing this circuit
the input voltage was reduced down to 5.5 volts and up to 7 volts while the charge voltage remained fairly
constant. This is a bonus if the power adapter you are using with your Psion is not precisely 6 volts.
Just do not use 7 volts for testing while the power adapter is plugged into the Psion otherwise you could cause
possible damage! Voltages too low (below 5.5v) will not make the Psion work and there is no way you should be
using higher voltages (7V+) while plugged into the Psion anyway.
Circuit components used
6 x (Six) 1N4148 small signal diodes
1 x (One) 220 Ohm (1/4 Watt) resistor
Thin heatshrink tubing to slip over the resistor and diodes (to stop shorting between series diodes)
Thin red coloured wire (20cm) for the charging battery (+) supply out terminal connection
Thin black coloured wire (3cm) for the link from the 5th series diode to the external power GND pad on the motherboard
***** IMPORTANT - Get the components together but do not make the circuit just yet! *****
Getting inside your Psion
The next stage you need to perform before making your circuit because you need to get an idea of how
small you need to make it and how it is going to fit. The space where this circuit is going to be located is an area
on the motherboard (the top if you have the Psion sitting up normally facing the bottom of the keyboard) on the left,
it is an area which has no components located just in front inside of the Honda serial port connector.
How do I get inside?
I came across a web page with a Japanese guy who demonstrates how to disassemble the Psion.
You can use this to help you take apart the Psion. He takes the whole Psion apart, but we dont need to go this far.
Simply disassemble the case until you can remove the mainboard, do not continue with the screen etc. You dont
need to take this apart.
Click here for the link for how to disassemble the Psion 5MX
Some of my own tips for you
- Be very very carefull with bending any plastic.
- Use your anti-static wrist band ALWAYS.
- Get yourself a container to place everything you have taken apart.
- To insert/remove the ribbon cable from the Psion you need to have the keyboard extended.
- I didnt need to remove the whole back plate, just the battery cover.
- Be very very carefull with all ribbon cables inside.
- Do not put stress on the screen or keyboard!.
- Take time when you disassemble and talk yourself into how you are going to put it back together again.
- Make sure the grey ribbon sheet is through the U slot when you assemble again.
- Do not put your hands/fingers on to the mainboard like Mr "Master" Muto does, keep them to the edge only.
- Try to use a desk with an anti-static surface mat also.
- Double and triple check case fittings and the steps you took when you disassemble the Psion.
- If something does not fit or wont fit, do not force it, take time to think first before you do.
- Try to handle everything as little as possible to reduce breakage and damage to circuits.
- The screw beside the Honda connector does not have to be put in again, this reduces stress from the circuit height.
- Try not to scratch the plastic case.
- You need to put the side tabs up and down to release and hold the keyboard and screen ribbon cables.
- Do not bend sharply the keyboard or screen ribbon cables.
- Have plenty of short breaks, there is no rush to do this and this will make you more accurate and make less mistakes.
- Put everything in a safe place when you are not working on a piece of the Psion.
- Make sure the baby or dog can not reach anything!
- Be gentle with everything you do, I did not need to force anything myself to get the job done.
- The third screw to remove the casing is under the warranty sticker by the battery backup cell.
- Use a lamp and/or plenty of light when working on the Psion.
- To remove the battery slider you need to slightly bend and push/pull out the plastic to insert/remove it.
- Try different ways when you find you cannot take something apart or fit it back together, there is a way.
The mainboard
When you have taken everything apart you should have the mainboard on the desk, when you first see
it it is not on the side we need to add the circut to. So turn it over and find the space above where the circuit
is going to go. You will now see the actual size of the space you need to fit your circuit onto. Use some sticker
paper and cut out a size to cover most of this space, this acts as an insulator to stop the circuit from touching
the circuits around it. This is very important to do.
Building the circuit
The best way to lay out the circuit is done by my example below, I solder the resistor to the middle
pad which helps to ensure the circuit stays in the one place and does not move around. The black GND wire is also
soldered to the top PAD (GND) and also helps a little to keep the circuit still on the mainboard.
As you can see, I have made the diodes into a loop to use the space better, make sure you solder the short black
wire to the end of the 5 diodes and then solder this to the top tab (GND). The red wire is connected to the
right most end diode and travels through the U slot just above the ribbon connector. I suggest you create your
circuit first before soldering anything onto the pads.
Here I am using a roll of solder to stop the components moving when soldering them together to form the circuit.
Testing the circuit
Before you attach your completed circuit you should connect a 6V DC supply to the circuit to test it.
Use another rechargable battery if possible, here (below) I use a 7.2V 100mAh battery pack to charge up to 3.3V.
Using your multimeter, you should monitor the battery being test charged. Watch the voltage of (discharged)
test battery increase to the 3.3v to 3.4v level. If you do not have a battery to test then place the multimeter
on the output (+) charge of the circuit and the meter should read more than 3V output (mine was 9v) because there
is no load. When you have a battery pack the output will not be a high voltage but rather the voltage is
increased over the charge time. In photo below you can see my circuit at the top right above the battery unit
being tested. +6V is connected to the end of the resistor and the GND is connected to the black wire end. If
you do not get the desired results then you may have contructed your circuit incorrectly or you may have a
soldering fault somewhere. (notice that the components are soldered together without any use of a circuit
board to place them on). You shouldnt really have much trouble getting this simple circuit created.
After everything is ok, you need to use some heat shrink tubing and cover the diodes so they are less likely
to touch by accident and create a short circuit. Use a lighter to shrink the tubing so it has a tight grip
around the diodes and wont move. Make sure before you put the tubing on, that you remove all sharp solder
spikes as these may puncture through the heatshrink tubing and create a short. You may have to bend straight
the diode array so you can put the tubing on, bend it back into shape again after you have shrunk it.
Next place the circuit on top of your sticker insultating paper and ensure it fits, allow for room at the bottom
of the circuit for the ribbon connector to fit into the socket. Adjust the diode array so that it fits nicely in
the empty space, make sure the circuit is close together so that it is far from the edges of the area.
Shorten the leg of the resistor and solder this carefully to the middle pad, the pad may need some more solder
added to grip the end of the resistor leg. Make sure you do not use so much that it shorts with the other pads.
Next solder the black wire end to the top (GND) pad and use the multimeter to check if the is a joint between
the top and middle pads, there should not be any conductivity between them, if there is you have used too much
solder and need to remove some and solder the pads again. Make sure the soldering is good and secure. The circuit
should not sit nicely on top of the space and should not be able to move around easily. Next place more sticker
paper around the circuit to ensure the circuit wire does not come into contact with anything else. You also need
add sticker paper to the top inside of the casing (it is conductive!) to form a sandwich insultation between
the bottom casing, the circuit and the mainboard. This is VERY important do make sure it is correct..
Thread the red wire though the U slot and turn the mainboard over.
Replace the mainboard back into the casing and connect the speaker, and battery ribbon cable.
Testing the Psion and circuit
Place the Psion on a flat non conductive surface. And plug in the 6V external power source.
The green keyboard light should come on as well as the Psion welcome screen. Attach the multimeter to the battery
terminal spring (-ve) terminal around the back of the Psion and the positive multimeter point to the red wire.
You should see the same voltage output as with the first time you tested the circuit. If this works it means
you have installed the circuit correctly and it is working. Next disconnect the power and solder the end of the
red wire to the +ve battery terminal. To do this locate the orange ribbon cable for the speaker and battery that
is at the opposite end and you will see a solder joint where the ribbon connector end by the speaker connects it
to the +ve terminal of the Psion battery contact. Make sure you do not melt the orange ribbon connector.
You need to be very carefull when soldering the red wire onto this!
Do not place the red wire length into the slot along the top of the Psion above the mainboard as this is where
the stylus slides in and out, you do not want to stop this from happening!
Drape the red wire across the mainboard, there is plenty of room inside the casing, that it wont effect fittings.
Assembling the Psion
Once this is complete, assemble the Psion again, replacing the bottom cover and everything else
turning it back to normal again. Insert your rechargable batteries and the backup battery.
Once assembling is complete, attach the multimeter to the +ve and -ve terminals of the battery compartment of the
Psion and attach the 6V power adapter. Note the voltage of your batteries, over time now they should increase in
voltage slightly as they are being recharged. When you see this happening, it shows the circuit is working and
trickle charging your Psions batteries.
Restoring the Psion
Now that your Psion is back to normal, you can restore the state of Drive C: back to how you had it
before, I backed my Psion to compact flash and restored it this way again easily resulting in all my applications
and settings back to normal.
The time test
Here are some voltages over time I recorded when testing charging the batteries using the completed project.
24 hr Time:
Voltage read
15:56
2.34
15:58
2.35
16:00
2.36
16:05
2.37
16:10
2.38
16:20
2.39
16:22
2.40
Stopped
--------
17:00
2.40
17:12
2.41
17:18
2.42
17:25
2.43
17:46
2.44
17:48
2.45
18:21
2.48
18:53
2.50
19:18
2.51
19:53
2.53
20:35
2.55
00:41
2.65
As you can see the battery voltage is increasing over time slowly as we trickle charge them.
Batteries of different capacity will vary in charge time also, these are Ni-MH 1300mAh types tested.
Batteries: NiCad/Ni-MH
The batteries I use are Ni-MH which are typically more expensive than NiCad.
There is some debate as to if the memory effect exists for NiCad batteries, you can make up your own mind about this.
If you can afford Ni-MH batteries then please purchase them over NiCad. The charger will work for both types of
batteries and needs no modification as well as for any other type of battery that can be constantly charged using
a small current in the same way. Since you should no longer need to remove batteries or buy more of them i would
recommend that you splash out on some high capacity (greater than my 1300mAh ones) Ni-MH AA's and use them on
your Psion.
Note:
Remember that now since you have done your modification and your Psion is now a chargable type, you
cannot use normal batteries in it, they must be rechargable ones and no other. If you place normal ones
in your modded Psion you risk them leaking, heating up and/or exploding (your Psion too!). You could place a sticker
on the back of your Psion explaining the modification and a reminder that only rechargable batteries can now be used
in the machine (HIGHLY RECOMMENDED!).
Use of the modification
Now that you dont need to replace your batteries in your Psion anymore (and save heaps of cash) you
need to be aware that you do now need to perform some regular checking of your rechargables. To ensure you do not
ruin your Psion you need to check every few weeks/months for the health of your batteries, make sure they are not
leaking and are in good condition. You should still check the battery status screen on your Psion and note the
voltage they are when you do your checking. If your batteries refuse to charge up, then check them visually and
try them in a normal charger, if they do not want to charge up then throw them away and replace them. Just because
you have an improved Psion does not mean you do not need to check regularly to monitor your batteries.
Conclusion
This project has resulted in an improved machine which stops Psion owners wasting time with battery
replacements and charging. I did not have much trouble performing the whole modification and I hope you will find
it easy and as trouble free as I have.
Feedback
If you have completed the project then please e-mail me and tell me all about it, I would love to hear
all those modding success stories! I cannot provide allot of help with this project via e-mail as everything you
need to know is written here. If you need extra help I recommend that you try your best first, ask others before
contacting me with your problems relating to this project. If you have any other ideas I would also like to hear
about them also.
Complete the form below and send it if you wish to contact me.
