idea for battery level indicator

I do not doubt this has already been implemented, so I'm not suggesting it is novel.

Why don't analogue battery level indicators show full until the battery discharges to a certain point? Then they could (maybe) change colors and then begin decreasing from full.

In other words...

... start with a battery level indicator bar

... have that bar remain the same color and appearance until the battery level drops to 50% or whatever

... at that point, change the color to red/whatever, and begin indicating further discharge by decreasing the length of the bar

The problem is real estate and LED electricity usage. That way you can use a shorter bar and change the bar's appearance only when the battery level is important. Most people can remember that they have recently charged the device. Before taking the device on a long trip or whatever, it should be left in the charger anyway. In other words, knowing that the device is full or nearly full is mostly useless, so there is no need to waste the space and energy by indicating that. The user mainly needs to know when to start looking for a charger.

Too many devices do not give enough warning before the battery needs to be charged.

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Reply to
John Doe
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This is a common problem in devices which:

[1] Depend solely (or primarily) on the battery's terminal voltage to measure/evaluate its level of charge, and [2] Use battery types which have a fairly flat voltage curve over most of their discharge range, and then die rapidly I think the commonest case is simple devices which are powered by NiCd or NiMH batteries, which have a fairly flat discharge curve. Lithium batteries have a similar issue.

In this sort of arrangement, it's simply rather difficult to evaluate the battery's true level of charge based on its voltage (open-circuit or under use-load). Until the battery is almost drained, it'll hold a near-constant voltage, and this doesn't give the measuring circuit much to work with.

More-expensive devices often deal with this issue by using a "gas gauge" IC - one which actually measures the charge flow into or out of the battery (using a low-value sense resistor, usually) and can thus deduce the remaining charge level based on a "known capacity, minus amount used since last full charge" basis.

You'll find this sort of gas-gauge approach used in laptops, and I suppose in some of the more sophisticated cellphones. It adds cost, though, compared to a simple voltage detector, and I'd guess that the low-cost end of many product lines won't incorporate it.

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Dave Platt                                    AE6EO
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Reply to
Dave Platt

If its a LED bar graph its not an analog level indicator. Provided its reasonably consistent, the continuous drop of the indicated amount remaining is extremely valuable as its easy to estimate time remaining. LED bar graphs are power hogs. A non-backlit LCD one can have negligable power consumption and much finer segments in less space and a single tricolour LED to flash (low duty cycle) amber then red for low battery and green when charging then steady green when in float mode at full charge can alert the user while remaining energy efficient.

NOTHING is worse than a gauge which indicates full till the battery is over half gone if you are away from base or easy charging. I have a couple of devices that do that and they are all a PITA and result in me carrying spare batteries. Ever driven on a long trip with a fuel gauge that showed full when it wasn't then started dropping suddenly? Its always so much fun wondering if you can make the next service station . . .

No doubt someone will like the idea - after all it got into a camera and some hand-held radios I use, but I'd suggest they've never been more than an hour from the nearest mains socket!

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Ian Malcolm.   London, ENGLAND.  (NEWSGROUP REPLY PREFERRED)
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Reply to
IanM

I do not feel like playing semantics. Whatever it takes, think "analog display".

That depends on size, Jack. Apparently you missed the point.

That is might be one reason why size matters. The main reason is electronic device screen real estate.

That's good unless you are constrained by space, or if the device sucks energy. I probably should not have suggested the meter power consumption would matter.

So make it when the battery is half gone.

I am not talking about dropping suddenly. I am talking about efficient use of meter size/space on an electronic device.

When you are driving on a long trip between gas stations, you fill up your tank first. Watching the fuel gauge during the first half of the trip between gas stations is nearly pointless. In fact, few people pay attention to the gas gauge until it indicates less than half full.

That analogy is weak because a car dashboard has lots of space and has no problem with meter size.

Get a car with better electronics, a bigger gas tank, or one that gets better mileage.

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Reply to
John Doe

Battery voltage is determined by the Nernst equation

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which means that the battery voltage depends on logarithms of concentrations of the chemical fule that is being consumed by the battery, whence the "fairly flat" discharge curve.

Batteries have internal resistance, which means that the observed output voltage is alos affected by current being drawn, and also that the internals of the battery are warmer than the environment due to the heat being disspated in the internal resistance. Since the Nernst equation also means that the driiving voltage is also a function of temperature, a battery fuel gauge needs to know the absolute temperature of the internals of the battery, it internal resistance (which can vary with the state of charge) and the current being drawn, if it's output is going to be of any use.

Since battery capacity decreases with increasing discharge rate, this approach also requres some complexity.

-- Bill Sloman, Nimegen

Reply to
Bill Sloman

It depends a bit on the amount of current drawn, as the battery has an internal resistance. I use a LED indicator on top of the _digital_ voltage and current readout on a bigger LCD. You do not normally watch that voltage all the time.. so the LED starts flashing when the voltage drops to 10.7 V (for a 12V sealed lead -acid), and at about 10.5 V or s, the power wll be cut, and the LED is constantly on. The flashing LED is a good way to get your attention, so you can do something, if you can, about the power

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The red LED is behind the 'Low Batt' text. All done with a PIC. :-)

Reply to
Jan Panteltje

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