200LX Power system FAQ

200LX Power System FAQ

1. Introduction
2. Backup Battery
3. Main Batteries
4. Adapter Power
5. Onboard Power Supply Considerations
6. PC Card Considerations

1. Introduction

The 200LX palmtop has an extremely complicated power system for its size. You may only put in the batteries and plug it in to the wall, but chances are that sooner or later you'll get to the computer's bad side, and need to read this. I did. There wasn't a power system FAQ, then.

An onboard battery meter (a kludged 6-bit ADC) gives very accurate battery voltage measurements for both the main and backup batteries, ranging from 1.57V to 3.30V, in .0286V increments. If you're paranoid like me, it pays to get a program like LXPro that you can pop up to read battery voltages without going into Setup (which isn't terribly accurate anyway.) LXPro can be found at SUPER.

2. Backup Battery

2.1. What is the backup battery for?

The backup battery maintains the system's RAM disk when no other power is available. This is normally when the main batteries are completely empty and the 200LX is not plugged in to the wall.

2.2. What is "Backup Mode" / "Exiting Backup Mode.." ?

It is a power-saving mode designed to prevent data loss. The theory is that the RAM disk of the 200LX (also known as the C: drive) needs power to maintain its contents. Most people value the contents of the C: drive and want to maintain them, at any cost. Even if it means their machine suddenly turns off and they lose whatever they were working on.

2.3. What triggers Backup Mode?

Any of the conditions which would require the system to run off the backup battery trigger Backup Mode. The main cause of going into "Backup Mode" is hot-inserting a PC Card, or in other words, inserting it while the machine is on. Most PC Cards cause a "spike" of current usage when they are first inserted which quickly settles down to their normal range. Often the spike is quite high; many cards draw over 100ma more than their operating current when first inserted. This quickly goes down to their normal operating specs, but even so, this very short current usage spike causes a voltage dip, which makes the 200LX think the batteries are very low. To prevent data loss, it hibernates.

The main culprits are 28.8Kbps and 33.6Kbps modems, or Ethernet cards. Occasionally flash cards have been known to trigger Backup Mode as well, but this is much more rare. Most 14.4 modems will not shut down the 200LX.

To prevent entering Backup Mode, the best thing you can do is TURN OFF the 200LX before inserting any cards!

2.4 What are the dangers of Backup Mode?

The most obvious danger is that your RAM drive will be erased. If you are plugged into a wall socket, your data is most likely safe. If you are on batteries, it's not so certain. Most of the time your batteries will have sufficient power to supply the C: drive's DRAM chips with enough electricity to maintain your data. This is because Backup Mode is usually entered long before your batteries are totally drained. (Contrary to a popular myth among 200LX users, Backup Mode does not force use of the backup battery. It will try all other power sources first.) However, if your batteries _are_ totally drained, or if your batteries have been removed, then the backup battery takes over. This is a situation you want to avoid, because:

In a typical situation, entering Backup Mode is equivalent to rebooting the machine. Hitting the [ON] key will bring the unit back up as though from a reboot. If your main batteries are too low to turn the unit on, you may hear a beep and see the screen flash, or you may see nothing at all.

If _every_ power source was too low to supply power to your RAM drive, your C: drive will be cleared and you will see the dreaded "Initializing RAM disk" message when you finally restore power to the machine.

Times2 Tech and Thaddeus 32MB upgraded machines are special in this regard. The above warnings apply to their on-motherboard RAM, which is highly vulnerable. The chips used for the 32MB drive, however, use less power than the built-in RAM and are a bit safer during power loss.

2.4. When should I change the backup battery?

Hewlett-Packard suggests that the backup battery be replaced annually. Really, it's not necessary to do so until the 200LX displays the message:


However, you should always have one handy, because once this message is displayed the backup battery may be only minutes from being totally empty.

2.4.1. When does the palmtop detect a low backup battery condition?

The 200LX displays the BKUP BATTERY LOW message when the backup battery's voltage has dropped to 2.80V.

2.5. How do I change the backup battery?

Pull the infrared cover off. This will reveal the infrared LEDs and the grey plastic backup battery tray. Pull the small tab with enough force to pull out the battery, but no more. The tray's tab tears very easily. The battery's type is CR 2032. Make sure that when you put the new battery in, the silver, labeled side goes _down_. Replacement is the opposite of removal.

2.6. Do I risk anything by not using a backup battery (other than loss of sanity from the incessant "BKUP BATTERY LOW" message?)

Yes. If the main batteries are too low to maintain memory, you will risk serious data corruption or loss. Basically, it's a Very Bad Idea. Don't do it.

3. Main Batteries

3.1. What are the main batteries for?

Without main batteries, the computer is forced to overload its internal fission reactor, which supplies most of the current. This leads to excessive radiation and may cause skin cancer. Unfortunately, the glowing effect from the reactor doesn't reach the screen, as the upper hinge is lead-shielded. So you can't use it as a backlight. Sorry, guys.

3.2. What kinds of batteries can/should I use?

The type of batteries you pick will seriously affect the running time of the computer. There are several different kinds of batteries. The first, which comes with the palmtop, is alkaline. A good pair of "industrial use" batteries will last a very long time. Plus, you have the advantage of being able to see the amount of power remaining via Setup, since alkalines drop in voltage as they are used. They generally are rated to be around 2000 mAh (milliamp hours). On the other hand, if you're willing to spend the extra money on a set of rechargeables, you'll probably be better off.

Nickel-Cadmium batteries (also called NiCd or nicad) have been around for a long time. NiCd capacity is usually around 600mAh. High capacity batteries are typically 850mAh. Panasonic high-capacity batteries are the highest power NiCds, at 1100mAh. NiCd batteries can be recharged inside the palmtop. They have a lower operating voltage than alkaline batteries (1.2V per cell instead of 1.5V) but provide a flatter voltage curve, which means that the voltage generally remains constant until close to the end of the life of the battery. This is good because you can use higher-drain devices without triggering a "Battery Low" warning, since the voltage remains high. However, it can be disastrous if you get the "Battery Low" warning, don't have a spare, and watch your batteries totally die a few minutes later.

NiCd batteries are subject to a memory effect, which means that charging them without fully discharging them first can damage them and lower your battery life.

Nickel-Metal-Hydride batteries (NiMH) are the next step up. You can go with basic RadioShack NiMH if you want; these garden variety batteries usually run around 1200-1300mAh. NiMH batteries have the same basic characteristics of NiCd batteries, being rechargeable and having a flat voltage discharge curve. However, they do not suffer from the memory effect and also come in higher capacities, so they have advantages. Newer NiMH batteries can be charged in the palmtop, when it is set to the NiCd setting. The downside is that most NiMH batteries have a high self-discharge rate; a fully charged pair left sitting for a week will discharge themselves down to nothing. Some newer batteries, notably Times2 Tech's high-powered 1350mAh NiMH batteries, overcome this and have virtually no self-discharge, thus providing us the best of all rechargeables.

Lithium AA batteries seem to be the longest-lasting in the 200LX. They have a discharge curve similar to NiCd and NiMH batteries, but last longer than even alkalines. They are not rechargeable, and are generally quite expensive ($4.50 and up for a pair).

3.3. What's up with the voltage meter when I use a PC Card?

This one is a bit hard to explain. Perhaps you've seen a coffee dispenser with a gauge of sorts, coming off the same pipe as the spigot. When you open the spigot, the coffee drains out of both the gauge and the actual container. Well, the battery meter works on the same principle. PC cards with high current drain will really mess up the voltage reading, while an SRAM or flash card will be practically undetectable.

3.4. When should I change/recharge the batteries?

You should change alkalines as soon as possible after the computer starts saying "MAIN BATTERIES LOW". You'll still have plenty of operating time if you can't change them immediately, however. When you really need to start wrapping things up is when it starts insisting "MAIN BATTERIES VERY LOW". Beyond that point, the system will eventually shut down. If you're lucky, there will be enough power left to keep it out of backup mode.

There's two different stories on rechargeables. Since the voltage curve is so steep on them, you need to get on AC power to recharge the batteries as soon as you get a "MAIN BATTERIES LOW" message. When you are using NiCd batteries, it is best only to recharge when the computer starts complaining, as intermittent recharging can permanently shorten battery life. With NiMH batteries, you can be safe recharging whenever you like, as they don't suffer from NiCd "memory effects".

3.5. Are there any external "power packs" available?

None commercially, though hobbyists have made some. With creative use of battery holders and such, you can, for example, run the computer from D-cell batteries. My opinion is that if the standard available power is not enough for you, it's probably in a situation where you would generally be running off an AC adapter anyway. In addition, you can't weld with the onboard power supply, so you might want to watch what you're doing if you get into that kind of situation.

3.6. When does the palmtop detect a low main battery condition?

According to the SDK:

The main or system battery consists of two 1.5 volt batteries in series. These batteries may be either NiCad or Alkaline, and feed the HP palmtop power supply in normal operation. The low main battery warning condition is nominally 2.2 (2.3 for NiCad) Volts. When the level reaches about 1.8 volts, the power supply can no longer reliably operate off of the main batteries, and an NMI Low Power In terrupt triggers a transition to Backup mode.

Because it is desirable to avoid warmstart, there is an intermediate state betwe en the first low battery warnings and the time of the Low Power NMI that MAY be entered. This state, called Software Shutdown, will be entered when the battery voltage reaches 2.0 Volts (NiCad or Alkaline). In this state the unit will be shut down, and attempts to wake it up will result in a pair of hi pitched beeps. Recovery from this state will not result in a warmstart provided that System Memory still appears to have integrity.

It should be noted that Software Shutdown is not triggered by hardware, but is instead the result of periodic battery measurements that take place every 15 seconds or so. Abrupt power transitions such as loss of battery contact, or very heavy loads being applied may result in a direct transition from a low battery warning state to BackUp Mode without ever entering the Software Shutdown state.

4. Adapter Power

4.1. What kind of adapter should I use?

If you are willing to spend $30-$35 on such an animal, then you should definitely go with Times2 Tech's tiny adapter. It's about as small as you can get, and its shape means it can be plugged in almost anywhere. It supplies 800ma of power (more than the genuine HP adapter!) which should be plenty for anything you do on the 200LX. The disadvantage is that it is not international-- it will only run on 120V, 60Hz AC current.

The next best thing is HP's adapter. It's light, portable, and is guaranteed to work with the palmtop in almost any country. There are cheaper solutions, but it's not necessarily a good idea to use them.

The onboard (that is, internal) power supply of the 200LX is very amicable. However, it is best to get an adapter as close to HP's specifications as you can. I have an adapter that is 9V, 300mA, and another that is 12V, 500mA, and both work fine. The optimal adapter is 12V, and at least 750mA. Make _absolutely sure_ that it puts out DC and has a negative (-) tip. We don't want any smoke, okay?

4.2. So what is all of this mA / V / tip stuff anyway?

mA stands for milliamps. An adapter's mA rating is how much current it can put out before it starts melting down (well, maybe not, but at least heating up a lot). You want a bare minimum of 300mA, if you aren't running any PC cards. If you are, I wouldn't use anything below HP's minimum spec of 750mA.

V stands for volts. The 200LX wants anywhere between 9V and 15V, ideally 12V. Too little will not be sufficient to power the unit. Too much could cause components inside to overheat and be destroyed.

The tip indicates the polarity of a barrel-style power connector. The tip is the bit that the needle on the palmtop sticks into. Since it's direct current, it _absolutely_ matters which way the power goes. The 200LX has a negative tip. With a positive-tipped adapter, you will likely destroy or severely damage the 200's onboard power supply. Don't forget. There's a diagram on the underside of the palmtop, below the connector, which shows the polarity, if you do forget.

4.3. What happens if I use an underrated supply?

Probably nothing. However, undervoltage and not having enough mA available does make the onboard power supply work a lot harder. Usually the upper-right area of the keyboard will start to get warm when this happens. Note that it will also get warm when charging batteries; this is not a sign of having an underrated supply. The other thing that will happen is the adapter itself will become very hot to the touch. If this happens, you really had better replace the adapter with a more capable one. (We're talking HOT here, not just warm. It's normal for an AC adapter to become warm when plugged in. If it burns your hand or starts smoking, though, that's a sign of a problem.)

4.4. I hear a buzzing noise from my unit. What is the deal?

Here we will get a little bit technical. The power supply which drives the screen also powers the PCMCIA socket. It buzzes in proportion to the amount of current it is delivering. Using a high-drain PC Card device such as a 28.8 modem will cause it to buzz louder, therefore, than it does when no PCMCIA card is installed. The loudness of this buzz is machine-specific. If it's too loud, you might want to have it checked out by HP or Times2 Tech. It's just not right for that small of a power supply to be making that much noise.

5. Onboard Power Supply Considerations

(Note: The rest of this FAQ is an answer. Deal with it. :)
The power supply on the 200LX is amazingly hardy. It can handle just about any input voltage, and produces a wide variety of output voltages. It can run an entire computer, and an expansion card to boot. All in a space that could easily be covered by a single quarter (sorry to break the news, but I'm in the U.S. Don't hate me for it.. :) Anyway, it's tough to destroy, but you don't want to try. Don't run a high-powered modem while plugged into a cheap adapter. Don't try to run a Type III hard drive on high-drain batteries. The power supply is your friend. Don't melt it.

6. PC Card Considerations

Many people wonder about the computer shutting down if a high-speed modem or another high-drain card is inserted while the machine is on. The answer is simple. Remember the coffee-pot analogy mentioned earlier? A high-drain card will bring the voltage meter down low enough to trigger a very low battery shutdown. If you shut the machine off before inserting the card, likely it will all power up in such a manner that it won't trigger a shutdown. If you can hot-swap a PC card, however, than by all means do. If the computer doesn't mind card-swapping, then it is a lot easier to do routine tasks like switching a modem out for a flash card. If you are unsure of whether your machine minds hot-swapping of a particular card, turn the palmtop on and stick it in. If there aren't any abnormalities, then you can feel safe doing it all the time. I have heard that 33.6Kbps modems often shut the machine down all the way to Backup Mode, so you'll want to make sure anything you're working on is saved to the RAM or flash disk before you start to experiment.

7. Acknowledgments

I would like to thank David Sargeant, Bill Childers, Davis Chapel, and Mack Baggette for the palmtop I'm typing this on.

Thanks again to David Sargeant for 33.6 modem and mA information and for fleshing out this FAQ where necessary, and to Davis for pointing out that I never mentioned some important battery voltages.

Thanks to what HP used to be before Hewlett died, we have this wonderful machine to gripe about when dealing with high-drain PC cards!

(c) 1998 Ian Butler
Advanced Software Systems, Inc.,
Peace love sunshine Volkswagen

Copyright 1999, David Sargeant.
Last Updated 2-21-1999

Copyright 1999, David Sargeant.
Last Updated 1-2-1999