HP-21 Circuit Diagram Schematic


I have found a circuit diagram for the HP-21. I don't know if it is accurate but it is worth a look if you are interested.


Click on the calculators link at the top of the page, then click the HP21 link and then click TD23 Data: view

That should get you to hp21.gif


Was anyone interested?

I would like to know if it is accurate.


... but missed the "Thank you" share. It's been quite noisy, busy morning here...

Thank you, Gordon; there are other good sources there.

Best regards.

Luiz C. Vieira - Brazil


Yes, thanks Gordon! I'm going to ohm out the common portions of my HP25 and then maybe I'll figure out a way to add the additional chips to the schematic.


Hi, Gordon;

I opened the file and I saw the additional circuit to suppress batteries when using external AC Adapter. It's the same one I was sent form another contributor. I know who is he, of course (thank you, R.) but I keep my policy of never mentioning a name associated to particular gestures before asking for permission. I know you all understand that.

But I was not aware about where did it come from, and now you, Gordon, have opened the box.

Thank you very much.

Best regards.

Luiz C. Vieira - Brazil

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