Finally acquired a Woodstock

[Chasfield]

Not an easy task in the UK. Brits were generally too poor to own HP calculators back in the 1970s and so many Woodstocks that got over here were 'ok until I plugged it in' just before they got listed on eBay. My HP-21 had been laid up for much of its life time and the pictures and description with the listing seemed to hint that the (deceased) previous owner knew about battery pack issues so I jumped in and bought it in untested condition.

It arrived today and it was apparent that the unit had been tweaked to run on dry cells, with the back plate of the battery holder partially separated and polarity markings added.

She fired right up and a wipe over with a damp cloth revealed The HP-21 to be in near mint condition. The battery terminals are perfect.

I was surprised by the compactness of the unit. How nice it is to pick up and use.

[jebem]

(10-25-2017 03:01 PM)Chasfield Wrote:  I was surprised by the compactness of the unit. How nice it is to pick up and use.

I bought my first HP 25C more than 40 years ago and I remember the huge satisfaction of using it. It just feels nice in your hand.

And the robustness of these models are among the best, despite the poor design choice in the power supply charger/adapter.

But that power supply design was common among other brands and equipment. I still have a professional Fluke digital meter from the 70's operated by D nicd cells that would fry the IC's if the unit was connected to the external AC power having the nicd batteries removed or in a leaking condition causing bad contact with the battery case terminals.
This is because the batteries are integral part of the power supply regulation and stabilization.
They did this to cut costs basically.

[Guido]

Congratulation!

The HP-21 was my first HP in the late 70th too and I still love it very much. The HP-41C was my next great step but died decades ago. I modifiyed my HP-21 to use standard AA cells and it worked very well for many years now. Only my eyes got a little bad in the last years so the LED display (I like very much the red LED's by the way) become too little for me, or the length of my arms to short. Now a HP-97 with much bigger display is on my desktop for a short time now (thanks to Adam J. !). And I love it!

Enjoy your new HP-21 as it is a very cool and reliable calculator for every day use.

[Craig Bladow]

Congrats!

I finally got an HP-25 last year and I love the LED display and the keyboard.

Enjoy!

[rprosperi]

Like Guido, the HP-21 was my first HP, so I can appreciate how you feel, about how it feels. From the 21, I upgraded to a 25C, then to a 41C, to 71B, and on and on. And while these machines have certainly improved in just about every way imaginable, there will always be something special and unique about how a Woodstock feels in the hand. If you never owned one, and you like LEDs, get one and give it a test drive; you will appreciate it too.

[PANAMATIK]

The "Woodstock" calculators are indeed perfect in their compactness. And I like their red LED numbers. In 1976 I bought my first HP-25. Also the printed manuals of these calculators were made perfectly. 25 years later I bought my second "Woodstock", an HP-21, still with some excitement, which I can share with yours. Have fun and enjoy this calculator.

Bernhard

[brickviking]

(10-26-2017 08:14 AM)PANAMATIK Wrote:  The "Woodstock" calculators are indeed perfect in their compactness. And I like their red LED numbers. In 1976 I bought my first HP-25. Also the printed manuals of these calculators were made perfectly. 25 years later I bought my second "Woodstock", an HP-21, still with some excitement, which I can share with yours. Have fun and enjoy this calculator.

Bernhard

Having had one of the Spice calculators (34C in my case), I can only imagine what it was like to have been one of the original purchasers of the Woodstocks. I hope you thoroughly enjoy using your HP-21.

I personally found that the LED display on the 34C was inadequate for use even in supermarket lighting, a somewhat frustrating situation considering I'd written my initial grocery program on it.

(Post 124)

[Gamo]

Hello
Craig Bladow

Congratulation!! Now you got the gem the HP-25

I don't have this calculator but got it as an app for Android called [ go25c ]
and this is a free app that I try for the first time. I noticed that this model
came with full Scientific / Engineer functions with very limited program steps
(49 steps) The only missing functions is the Factorial (n!) which is kind of weir that this model doesn't have. The Owner's Manual even included on how to program with Finding the Factorial Number Program as an Example.

I'm surprised that this model came with full Conditional Test.

Gamo

[BobVA]

(10-31-2017 11:45 AM)Gamo Wrote:  ... with very limited program steps
(49 steps) The only missing functions is the Factorial (n!) which is kind of weir that this model doesn't have.

I'm guessing the small number of program steps was due to the lack of continuous program memory, meaning you had to re-enter a program if you turned the calculator off.

I kept a tiny notebook in the case with my HP-25 as my "non-volatile" program storage. And I remember the manual's suggestion to press "1" in RUN mode to minimize current draw if the calculator was kept on to just to preserve memory.

As for factorial, that's an interesting question. TI obviously thought it was an important function for general use (it was on the TI-50), but HP clearly didn't share their enthusiasm. I think the first HP with factorial was the HP-65?

[Geoff Quickfall]

Yep,

HP 25 as my university entry calc. It was a must have for the stats course. Slide rules were abandoned in that course the previous year (1976).

Sold it to help finance a 41 in 1979 which I bought from a company called Elektek (if memory serves me correctly)

Then, in 1993 I found, yes found an HP 25C in a garbage can (dumpster diving) in the flight planning room, the garbage can empty except for the cal. Yes, some one had thrown it out as the battery pack had died. Two new alkalines and a clean of the spring contacts and it was up and running.

The lunar simulator was my first computer game! Of course I hacked it for more fuel.

;-)

[Craig Bladow]

Hi Gamo,

Having gone through the user manual and “HP-25 Applications” it turns out there is a lot that can be done in 49 steps. Memory was expensive and since the program was lost when the calculator was turned off, 49 steps was probably thought as a reasonable maximum amount to ask the user to key in again and again.

I also am pretty sure the factorial program in the user manual can be done in fewer steps

[rprosperi]

(10-31-2017 04:15 PM)Craig Bladow Wrote:  Hi Gamo,

Having gone through the user manual and “HP-25 Applications” it turns out there is a lot that can be done in 49 steps. Memory was expensive and since the program was lost when the calculator was turned off, 49 steps was probably thought as a reasonable maximum amount to ask the user to key in again and again.

I also am pretty sure the factorial program in the user manual can be done in fewer steps

In college, I found out 2 important things about the HP-25 Program Memory space:

1. You really can do a lot in 49 steps.

2. You can do about 10 times more in 50-52 steps! No matter how hard I tried, many of my more complex program attempts were often 1, 2 or 3 steps more the 49-step limit.

If I had some of the Dieter's (and many other folks here, but let's face, he's legendary with this) step-saving tips I probably could have squeezed more in, but alas, though really good, these came along 35-40 years too late.

[Steve Simpkin]

(10-31-2017 11:45 AM)Gamo Wrote:  I noticed that this model came with full Scientific / Engineer functions with very limited program steps (49 steps) The only missing functions is the Factorial (n!) which is kind of weird that this model doesn't have. The Owner's Manual even included on how to program with Finding the Factorial Number Program as an Example.
I'm surprised that this model came with full Conditional Test.

Consider that the HP-25 was originally planned to be a non-programmable advanced scientific model. By including programmability, the engineers used up almost every word of code storage space (2048 microinstructions). There was no room to include additional features without removing something else.
http://www.hpmuseum.org/journals/wooda.htm

[Geoff Quickfall]

Most of my 25 programs required 50 lines :-(

My 29C program's needed 99 lines,

My 67 programs needed 225 program steps,

My ...



:-)

[Chasfield]

I have adapted the HP21's battery compartment to use a pair of AAAs. The original battery carrier would take AAs through its partially detached base plate but the latter was left flapping in the breeze (the PO cured this with a strip of tape) and battery swapping was a bit fiddly. The other issue is whether or not the 3.2 volts delivered by fresh alkalines is too hot for the 2.5 volt calculator circuit. I could find no certain answer to this question, so I installed a cut down, three-cell AAA battery carrier and used the spare space to add 2.8 ohms of series resistance that can be shunted out with a slide switch when the batteries have lost their edge. This resistor arrangement shaves ~ 0.3 to 0.5 volts off a pair of brand new cells, depending on current draw. Once the the calculator shows a low battery condition the resistor can be switched out to let the batteries run down to their normal low voltage state. This may be a solution looking for a problem but it doesn't hurt anything and will marginally extend total battery life.

Beware of very cheap battery holders. Mine has crimped connectors which lost crimp pressure when I got too near their supporting plastic with the soldering iron. I had to jumper an unexpected open circuit with copper wire.

With the exception of a 3 mm hole in the battery compartment cover, the mod is reversible - as long as I can lever off the epoxied in retaining screw boss. The battery carrier is located by a couple of foam sticky tabs.

[mfleming]

I use a pair of Eneloop NiMH rechargeables. They don't have the self discharge problems of NiCd batteries so they last longer under light use conditions. Works for me, anyway! On the subject of battery holders, I stumbled upon this very nice one-piece design

https://www.thingiverse.com/thing:1276886

I uploaded the design to Shapeways, made a small correction and ordered one for under ten dollars. Two batteries fit snugly side by side. I used a pair of connected coil springs to connect the batteries together and press them against the calculator battery contacts. The springs are replacements for those used in HP-41 battery holders. The battery holder fits into the calculator very nicely!

This design will save you the bother of taping the two-piece holder design together each time you change the batteries. The plastic used is supposed to absorb paint very well so I may soon try to match the calculator body color.

I highly recommend the holder,
~Mark

[Geoff Quickfall]

Nice holder Mark,

Alkaline voltage is not a problem at 3.2 - 3.5.

Anecdotal yes, but my garbage can find of the 25c has been running on alkaline AA replacements since 1994 as have many of my other woodstocks. All Panamatik's woodstock ACTs are designed for the voltage also.

I have recently switched all my woodstocks to rechargeable NiMH which are charged enmasse with an external charging unit. The rechargeable batteries used for convenenience, not voltage concerns.

Cheers, Geoff

[aurelio]

(10-31-2017 04:12 PM)Geoff Quickfall Wrote:  The lunar simulator was my first computer game!
;-)

+1, the first and the only one

my first 25 (c) in the 1976 at college and what a nice companion till the teacher realized I was playing with the brother of his own calculator (a 25) and it was banned from the classroom , while performing evaluation tasks (they were not allowed for obvious reasons).
The good was that we began to share programs from that time, the bad is that never I met at the university a teacher like him.

Compliment for you new woodstock, Chasfield
My 25c is still in a good shape, just a sign (a too close encounter with a soldering iron tip) and now working (as well as you did for your HP21) with alkaline cells

[larthurl]

(11-06-2017 03:37 PM)mfleming Wrote:  I use a pair of Eneloop NiMH rechargeables. They don't have the self discharge problems of NiCd batteries so they last longer under light use conditions. Works for me, anyway! On the subject of battery holders, I stumbled upon this very nice one-piece design

https://www.thingiverse.com/thing:1276886

I uploaded the design to Shapeways, made a small correction and ordered one for under ten dollars. Two batteries fit snugly side by side. I used a pair of connected coil springs to connect the batteries together and press them against the calculator battery contacts. The springs are replacements for those used in HP-41 battery holders. The battery holder fits into the calculator very nicely!

This design will save you the bother of taping the two-piece holder design together each time you change the batteries. The plastic used is supposed to absorb paint very well so I may soon try to match the calculator body color.

I highly recommend the holder,
~Mark

Hello Mark:

do you have a link to the shapeways version of the HP-25 battery holder you did?
I'd like to get one for my Dad's HP-25.

Thanks

.....Art

[mfleming]

(01-08-2018 10:06 PM)larthurl Wrote:  Hello Mark:

do you have a link to the shapeways version of the HP-25 battery holder you did?
I'd like to get one for my Dad's HP-25.

Thanks

.....Art

Hi Art,

I struggled quite a bit to set up a Shapeways shop to make the design available for order (no markup) or download. Quite a pain! Try this link and PM me if there are problems. You'll like the case - no tape to hold the halves together.

https://www.shapeways.com/product/6NQAST...d=64514022

~Mark