Woodstock Display Upgrade (a sight for sore eyes)

[markhen]

The calculator's interface to the display requires a lot of pins (8 segments and 12 digit selects (although not all 12 are required if we use some trickery)). There is only so much room under the display board where chips can be squeezed, so it has to be small packages, consequently with a small number of pins. The displays used here have a serial interface, requiring 5 pins, some (like the HPDL1414) have a parallel interface that requires lots of pins (over a dozen). Every pin on my CPU is used, none left over! Not to mention the physical constraints on the display size, it's quite a fluke these displays fit!

I've thought about a similar retrofit for Classics, but their LED interface is very special (inductors!) so making something that could plug in is questionable.

[albertofenini]

Super cool and very nice, well done !
When are you going to sell those ?
take care !!

[agarza]

WOW! Super Cool!

[markhen]

Thanks to all for the kudos, this is a fun project.

Since my first post I have been using the modified 25 as my "daily driver" and I must say it is my favorite calc by far :-) I made a small circuit board that allows me to pack 1800mAh LiPo battery (2P1S) into the original case (pic attached), charged externally (naturally...). So far I have several weeks of daily use without needing to recharge.

I haven't made firm plans to produce this as a kit yet. Since the components are expensive, it's not clear to me how many people would be willing to pay something like the cost of a working HP25 on that auction site to add this display functionality? It was definitely worth it to me, but I am the proud father ;-)

[Harald]

(09-29-2022 05:34 PM)markhen Wrote:  I made a small circuit board that allows me to pack 1800mAh LiPo battery (2P1S) into the original case (pic attached), charged externally (naturally...).

Can we get more information on the battery pack? What battery did you use? So you have spare PCBs and a list of components?
I would really like to make a couple of these battery packs!

Cheers,
Harald

[markhen]

I do have a couple of unused PCBs (and easy to make more), the board requires soldering of some small surface mount diodes and connectors, also getting it all into the battery case is a bit fiddly - all this is ok for folks experienced in these things, but not for everyone. Also an external LiPo charger is required with a specific cable. Let me think a bit about how this could be made more “user friendly” !

[Stefan_Titan2944A]

(08-07-2022 10:47 PM)markhen Wrote:  The display module has 2 “content enhancements”, when activated by the touch/proximity switches:

“RUN” Mode Display Enhancement
(...) the module will not display the numeric exponent, but will instead display an up arrow (for exponent) and the alphanumeric SI prefix.

Well done - looks great - very nice!

Regarding ENG mode:
"µ" and "n" - I suppose "G", "M", "k", "m", "p", "f", "a" are available as well -
are a great and welcome improvement.

Nevertheless, what's the "up arrow" for?
Does it replace an "E"?
Can't / shouldn't it be omitted?

E-06 (10^-06) is not equal to Eµ (10^(10^-6))

1.234 µ is fine!

[BobVA]

(09-29-2022 05:34 PM)markhen Wrote:  ...Since my first post I have been using the modified 25 as my "daily driver" and I must say it is my favorite calc by far :-) I made a small circuit board that allows me to pack 1800mAh LiPo battery (2P1S) into the original case (pic attached), charged externally (naturally...). So far I have several weeks of daily use without needing to recharge...

Very nice!! I'd be interested in a kit, PCB, or just a board design and a BOM.

Can it supply a continuous low stand by current (e.g. for a 25C)? Or is it designed to switch off entirely when the main load drops? Is there much parasitic drain when off?

Regarding the display price, I've got a 29C with a GPS receiver in it that suggests a small, but highly enthusiastic, market for such things :-)

Again, very nice work on both and thanks for posting!

Bob

[Didier Lachieze]

Very nice display !

As the dot is using a digit location, I suppose that for negative numbers you’re loosing the rightmost digit.

[markhen]

@Stefan - I've implemented all the defined SI prefixes (Y,Z,E,P,T,G,M,k,h,da,d,c,m,mu,n,p,f,a,z,y). I debated for a while whether to have some sort of "exponent follows" marker - or not. After playing around with various options I liked the up arrow. I agree that no marker is really required, but I think when first using this mode it's a bit confusing to see a single letter "floating" out on the right?!? Very easy to remove that marker!!

@BobVA - the battery pack circuit is dead simple - see attached. I use 2 x 3.7V (nominal) 900mAh LiPo cells connected in parallel. They are a SNUG fit in the battery case, which needs a little surgery to make the battery opening larger. The charger connector is mounted on the circuit board in the pack (0.1" header) and charger cable can be inserted either way (for safety/convenience). Fully charged cell is ~4.2V, the 2 x silicon diodes drop a bit more than 1.2V under load, so the calculator doesn't see over 3V (under load). This is the same as it would see if using 2x fresh alkaline AA cells, and we know the calcs work fine on this voltage. When the batteries drop to 3.7V (which is about where we should recharge), the calc sees about 2.5V, which is higher than the calc low battery threshold, so the low battery indication now really means "stop and recharge NOW"!! As you can see, there is no inherent parasitic drain in the battery pack itself, and it will supply standby current for 25C or 29C models. I've been using this in a 29C with no issues. I guess there is a concern in the C models that since the standby current draw is very small, the diode drops will be <<0.6V, and the CMOS memory will see something like ~3.6V with a fully charged LiPo? Accidently plugging the calc into a standard charger will not damage the battery pack (hopefully no one here does this with Woodstocks FOR ANY REASON nowadays?!) but will almost certainly damage the calc :-(

@Didier - I mentioned this in post #12 - "The code looks at the calculator display and decides if it has enough display digits to display all visible digits, or not. If there is no minus sign on the mantissa, it will use the left-most display digit to display a digit (this is something the base calculator never does (in "RUN" mode)). In the event the display mode and display value exceed 12 digits, the least significant digit is dropped (truncated). This could easily be changed to round (vs. truncate)." This is probably a pretty rare case for most users?

[GreyUser]

I have a batch of HPDL-1414 that I bought for about $0.75 US each awhile back with plans to grind them down to fit. It looks promising but I’ve never gotten to the project. Unfortunately, the days of plentiful, cheap HPDL-1414 on Aliexpress appear to be over.

[Matt Agajanian]

(08-07-2022 10:47 PM)markhen Wrote:  The display module has 2 “content enhancements”, when activated by the touch/proximity switches:

“RUN” Mode Display Enhancement
If the calculator is displaying an exponent (in the right-most 3 digits (sign, digit, digit), and the exponent matches an SI exponent prefix (10^24 .. 10^-24), the module will not display the numeric exponent, but will instead display an up arrow (for exponent) and the alphanumeric SI prefix. Since I work most of the time in ENG notation, this is SUPER handy!!

Hi. Any chance that SI unit characters can be a preference setting between the usual sign & exponent display and alpha SI prefix?

[markhen]

@Matt - yes, already done - as described in posts #2 - #4 there are 2 capacitive switches accessed by touching the top of the calculator - one turns on the SI mode, the other turns it off (back to normal exponent display). At the moment the default is to normal display mode (when calculator is turned on - there is no memory of mode during power off).

[Matt Agajanian]

Markhen, good to know.