Question to HP-35 owners

[Willy R. Kunz]

(02-07-2015 09:47 PM)PANAMATIK Wrote:  

(02-07-2015 08:52 PM)Willy R. Kunz Wrote:  Alright, then, you might be the right person to come up with the final answer to the question this thread is all about: which decimal points are lit when the battery charge drops below a certain level? Do they just invert, as WalterB suggests? Or do they show up in the way the HP-35 manual states (see attachment)?

One more question: if you plug in the power adapter, does the battery warning disappear immediately, or only when the battery charge crosses the trigger level again?

My guess is that HP chose a simple hardware solution: XORing the decimal point signal with the output of the voltage detector. No software involved at all.

I'd love to make my HP-35 simulator behave like the real thing.

Hello Willy,

I plugged my HP-35 SNr 1143S to my power supply with variable Voltage output. The level where the dots come up is about 3,65V. The nominal Voltage is 3,75V. If I reduce the voltage the dots slowly appear, some of them earlier than others, but within about 50 mV below the threshold all of them are there.

To my surprise it does neither inverting the decimal dots nor it does show all decimal dots. It shows all dots except the one following the original numbers decimal dot. The original dot is not inverted. if you press CLX you see .0. ........... . (The last dot is the punctuation mark). If you press any key while in low battery mode, the invisible dot will be shown for 100 ms, then vanishes again.

You don't need to press a button for showing the low battery signal, it appears as the voltage drops, other than the HP-25, where you need to press a button for sampling the battery voltage.

I cannot tell you whether all versions of HP-35 show the same behaviour. My HP-35 version doesn't show HP-35 on its front label, only the name Hewlett Packard.

The HP-35 manual is also right, it shows exactly at number 2 the dot is missing, that is one digit right of the decimal dot.

Bernhard

Wow. Great answer, thank you so much.
So you have a version 1 or 2 HP-35, depending on whether you see the red dot or not. And the manual's illustration is correct, not the statement on page 28! Very surprising, to put it mildly.
Well, then, a nice software challenge. Totally irrelevant, but fun.

Willy

-- Dem Inscheniör ist nichts zu schwör.