HP97 The journey begins
|
11-21-2021, 12:43 AM
(This post was last modified: 11-21-2021 01:44 AM by teenix.)
Post: #515
|
|||
|
|||
RE: HP97 The journey begins
Hi all,
Now that the 97S interface seems ok, I will move on to the last part which is the IR print interface. I have written some code which looks ok on the oscilloscope, but until recently I had no way of testing it. I have to say, the generosity of some Forum members that have helped with this project is quite humbling. The other day a package arrived at my door with some donated HP 82240A/B printers which will provide the means to complete this part of the project. TC a HUGE thanks. The only problem I can foresee is the timing for the link. Looking at the old Journals, this seems to be critical. It appears that the calculator mentioned in the article was a HP-18C which has an inbuilt 32KHz crystal oscillator from which to base the timing. The IR print signal is also used by the printer firmware to adjust for small discrepancies with its less stable RC oscillator. The 97 CPU board timing is based on an internal time base generated by the PIC. This is also relatively unstable as the frequency will drift a bit with temperature and supply voltage fluctuations. An external crystal could be used, but adds cost and there are no free OSC pins available. Hopefully the printer software can still sync itself to a slightly varying signal. If the interface works, I might be able to add an IR printer link to the 65 and 67 boards. These will be a bit difficult because there was no printer to start with. Edit: The world wide semiconductor shortage has caught up to me now. The PIC CPU used in the 97 board is now not available until late 2022. Others that might be used as substitutes are also not available. I only have a few on hand so I can only make up that many until new devices become available. This is also affecting the other CPU boards. :-( cheers Tony |
|||
« Next Oldest | Next Newest »
|
User(s) browsing this thread: 2 Guest(s)