Lately bought a HP-25 with an interesting mod of the battery case done by a previous owner (hardware and software specialist).
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attachment=3901]
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Anybody aware of that?
I took the risc and hook the calc to the power adapter.
It worked perfectly.
interesting. I wonder what the diodes are for. they might protect the caps from overvoltage?
(09-10-2016 10:34 AM)damaltor Wrote: [ -> ]they might protect the caps from overvoltage?
Rather the calculator! This looks like a fairly primitive circuit for smoothing the current (capacitors) and limiting the voltage to the calculator (diodes, maybe one of them a Zener-diode?). I would not want to use any of my woodstocks like this, rather connect them to a properly regulated and protected power supply set to 2.5V. Or, as I prefer, use it with externally charged batteries and hide the original chargers very deep inside some drawer...
I have just been rebuilding the power circuits in a bunch of HP-21's and this looks like the substitute for batteries circuit from
http://www.cs.ubc.ca/~hilpert/eec/calctd/HP21.pdf.
The Si diodes each have ~07.V drop which get you up to the 2.1-2.8V range.
(09-10-2016 10:59 AM)Maximilian Hohmann Wrote: [ -> ] (09-10-2016 10:34 AM)damaltor Wrote: [ -> ]they might protect the caps from overvoltage?
Rather the calculator! This looks like a fairly primitive circuit for smoothing the current (capacitors) and limiting the voltage to the calculator (diodes, maybe one of them a Zener-diode?).
Agreement. It is a workaround as woodstock's power adapter delivers ac and too much output voltage for directly driving calculator. Some capacitors and diodes can do ac/dc conversion and voltage cut. Nevertheless curcuit looks frightening simple ;-).
P.S. Found a similiar curcuit in an HP19C (Only 1 capacitor and 1 diode ;-)) and it is (after remodifcation) still alive...
IMO, those capacitors should be replaced before you use that calculator much longer. They look rather old, and electrolytic capacitors don't have an indefinite lifespan (often 10-20 years, sometimes 30-40 if you're lucky). Use values as close as possible to the existing caps, to be safe. Might not be a bad idea to replace the diodes, while you're at it. Make sure to match the polarity of the new parts to how the old ones were wired in.
-Adam
(09-12-2016 02:26 AM)rprosperi Wrote: [ -> ] (09-12-2016 01:19 AM)Nate Martin Wrote: [ -> ]Top:
https://www.shapeways.com/product/ZKFJHGDJM/
This link seems to be bad; at least it was for me.
Once released, will you add these into the existing store that has the 41C and 71B parts?
I am doing small adjustments to the bottom, once I have them working well I will open up to everyone.