Author Topic: EEVblog #1159 - World's Most Precise Pocket Calculator  (Read 4292 times)

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Online SiliconWizard

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Re: EEVblog #1159 - World's Most Precise Pocket Calculator
« Reply #50 on: January 03, 2019, 07:05:00 am »
I have now replaced C5 and C6. That helped a lot, the current consumption is now ~4.5uA when off.

That was quite a leakage! About 125µA... What kind of capacitors were they?

I have not seen any possibility to turn the screen off, but I haven't looked hard either.
Anyway, I don't think it's necessary given the "calculator off" current consumption and the battery capacity.

Yes, that's interesting actually. If I got it right, the screen must be a Sharp LS027B7DH01. From the datasheet, its nominal supply voltage is indeed 5V as I remembered. They state a typical static power draw of 50µW.

If the DM42 is powered by a single CR2032 cell (is it? or is this 2 cells?), then it must have a step-up regulator for powering the screen. The typical total static current draw on a single cell would probably be over 50µA (and assuming a very low power step-up reg). So I'm thinking they may have found out that the screen retained its image down to a much lower voltage than 5V, at a much lower power draw than the typical. I don't think I have seen anything about this in the datasheet which is kinda minimal. I would be interested in knowing more about this, as I've used this kind of screens but never thought of the possibility of leaving them on at all times (while on batteries) due to a bit too high static current draw (but I never bothered to fiddle with supply voltage and such).


 

Offline Thomas

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Re: EEVblog #1159 - World's Most Precise Pocket Calculator
« Reply #51 on: January 03, 2019, 07:06:53 pm »
I have now replaced C5 and C6. That helped a lot, the current consumption is now ~4.5uA when off.

That was quite a leakage! About 125µA... What kind of capacitors were they?

I have not seen any possibility to turn the screen off, but I haven't looked hard either.
Anyway, I don't think it's necessary given the "calculator off" current consumption and the battery capacity.

Yes, that's interesting actually. If I got it right, the screen must be a Sharp LS027B7DH01. From the datasheet, its nominal supply voltage is indeed 5V as I remembered. They state a typical static power draw of 50µW.

If the DM42 is powered by a single CR2032 cell (is it? or is this 2 cells?), then it must have a step-up regulator for powering the screen. The typical total static current draw on a single cell would probably be over 50µA (and assuming a very low power step-up reg). So I'm thinking they may have found out that the screen retained its image down to a much lower voltage than 5V, at a much lower power draw than the typical. I don't think I have seen anything about this in the datasheet which is kinda minimal. I would be interested in knowing more about this, as I've used this kind of screens but never thought of the possibility of leaving them on at all times (while on batteries) due to a bit too high static current draw (but I never bothered to fiddle with supply voltage and such).
C5 and C6 are ceramic capacitors, 100uF, 1210 size, probably X5R type. They don't leak 125µA DC (I tested after taking them out) but I think they have high dielectric losses.
I replaced them with 10uF X7R type, works fine.

The calculator is powered from a single CR2032 cell.
You are probably correct they are running the screen at a lower voltage when off, just for retaining the image.

For more information, check this thread over on HPmuseum.org:
http://www.hpmuseum.org/forum/archive/index.php?thread-10143.html
 

Online Kean

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Re: EEVblog #1159 - World's Most Precise Pocket Calculator
« Reply #52 on: January 03, 2019, 09:43:10 pm »
May not be leakage of the capacitors, but from flux residue - or a combination of the two.
 

Offline EEVblog

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Re: EEVblog #1159 - World's Most Precise Pocket Calculator
« Reply #53 on: January 04, 2019, 12:47:54 pm »
I was hoping this leakage thing could be video worthy, but just measured mine and only got 5uA. I hate when stuff works  ;D
 

Online Kean

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Re: EEVblog #1159 - World's Most Precise Pocket Calculator
« Reply #54 on: January 04, 2019, 04:38:55 pm »
I hate when stuff works  ;D

Those of us who create and ship products think a little differently!   :phew:
Actually, you do that too...  :-DD
 

Offline Thomas

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Re: EEVblog #1159 - World's Most Precise Pocket Calculator
« Reply #55 on: January 05, 2019, 06:04:57 am »
I was hoping this leakage thing could be video worthy, but just measured mine and only got 5uA. I hate when stuff works  ;D
Too bad your unit is OK :-DD I think that could have been a great video, as I think quite a few people are experiencing this issue.

Swissmicros asked if I felt competent to replace the capacitors myself, which I said yes to. They said it would not void the warranty, and they would be happy to send the caps to me. No need for that. Easy for me, easy for them.

Refreshing to see this kind of support in this day and age. Especially for this kind of product.
 

Online SiliconWizard

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Re: EEVblog #1159 - World's Most Precise Pocket Calculator
« Reply #56 on: January 05, 2019, 12:41:44 pm »
Swissmicros asked if I felt competent to replace the capacitors myself, which I said yes to. They said it would not void the warranty, and they would be happy to send the caps to me. No need for that. Easy for me, easy for them.
Refreshing to see this kind of support in this day and age. Especially for this kind of product.

Yes, it's very impressive. The fact that even merely opening the case would not void the warranty is a big plus, not to mention replacing components. Of course they saved some of their own time, so that was a win-win. Kudos to them.
 

Offline EEVblog

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Re: EEVblog #1159 - World's Most Precise Pocket Calculator
« Reply #57 on: January 05, 2019, 04:56:38 pm »
I was hoping this leakage thing could be video worthy, but just measured mine and only got 5uA. I hate when stuff works  ;D
Too bad your unit is OK :-DD I think that could have been a great video, as I think quite a few people are experiencing this issue.

Yep, very dissapointed!

Quote
Swissmicros asked if I felt competent to replace the capacitors myself, which I said yes to. They said it would not void the warranty, and they would be happy to send the caps to me. No need for that. Easy for me, easy for them.
Refreshing to see this kind of support in this day and age. Especially for this kind of product.

 :-+
 

Offline Leo Corradini

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Re: EEVblog #1159 - World's Most Precise Pocket Calculator
« Reply #58 on: January 06, 2019, 07:21:37 am »
I just love being able to print on my hp 82240B printer with the hp42s!
 


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