wp34s low battery threshold Increased to 2.7V

[Jeff O.]

I note that with build 1737, the low battery threshold was increased to 2.7 Volts. Why? What was it before? Do I need to replace my batteries when the indicator lights up?

[Marcus von Cube, Germany]

It had reports of strange behavior at various voltage levels, so I decided to increase the threshold. It not only displays the indicator, it also reduces the maximum speed and therefore the stress on the batteries. If I knew precisely at what voltage the problems with full speed start I could set the threshold to that point, but I have no dependable information about it.

In short: With BATT on, you can still operate your 34S safely but it will not be as fast as with new batteries.

Maybe I'll add another modification: Increase the operating speed only after a short delay so that routine stuff like data entry and simple operations will all run at 2 MHz which should be light on batteries. This will need some testing though to find the right compromise between (perceived) speed and power consumption.

[Jeff O.]

What if I am in a situation where I need to have the answer to some life or death problem (such as determining the number of pixels in a circle) as quickly as possible, yet my battery voltage is at 2.7 Volts and I have no new batteries? Would it be possible to have a flag or setting that would leave in high-speed mode regardless of battery voltage? Or maybe let me set the low battery threshold wherever I want, with the default being 2.7 Volts?

Edited: 19 Oct 2011, 11:56 a.m.

[Marcus von Cube, Germany]

For death or life problems you should not use WP 34S. ;-)

We have no room to store such a threshold. If anybody can give me a valid value for the threshold below which running at more then 30 MHz will cause reliability problems and above which these can be ruled out, I'm a taker.

[Jeff O.]

Quote:

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If anybody can give me a valid value for the threshold below which running at more then 30 MHz will cause reliability problems and above which these can be ruled out, I'm a taker.

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I will not claim to be an expert, but, in perusing the CR2032 data sheets from various manufacturers
(available here), many of them mention an end point voltage of 2.0 Volts. I don't propose going that low, but if you examine the discharge curves, it looks like 2.5 Volts might be a reasonable value to use as the low-battery threshold on wp34s.

[Marcus von Cube, Germany]

Jeff, I did a recent updat to change it back to 2.5V. While testing a lengthy program with weak batteries which normally do not light the low battery indicator, it started flashing randomly during the computation. BATT reported 2.7V. It looks like the current draw on weak batteries has a noticeable effect on the voltage.

[Paul Dale]

Was that in SLOW mode?

What about start slow mode at 2.7 or 2.8 volts. Light the low battery indicator at 2.5?

I know confusion will occur when the device suddenly runs slower but it seems a shame to waste batteries needlessly.

- Pauli

[Marcus von Cube, Germany]

It wasn't in SLOW mode. I vote against an automatic but invisible speed throttle. The calculator was still working perfectly. If you want to deliberately save battery power, use SLOW as a setup command.

What I'm thinking about is a delayed speed up for manual operations so that the speed will remain at 2MHz unless an operation takes more then .2s. Maybe even a two step approach.

[Walter B]

Even in SLOW mode the WP 34S works faster than you can key in a problem. And please note you can keep a fire door open for several minutes by a WP 34S with battery voltage <<2.7V as well ;-)