A simple (and useless) digital circuit for the fans of the HP-15C (and two other HP calculators) « Next Oldest | Next Newest »

 ▼ Gerson W. Barbosa Posting Freak Posts: 2,761 Threads: 100 Joined: Jul 2005 10-17-2011, 04:37 PM I'm back to school for lack of something better to do (I'd rather be vacationing in southern France or Tuscany :). Lots of things have changed: one of my classmates in 1986 and 1987 is now my professor of Digital Electronics, for instance, and back then we used DOS PSpice :-) After finishing my homework exercises on digital counters I decided to design a counter to cycle through the names of my first, second and third HP calculator. My first idea was doing it with three synchronous counters, for the two digits and characters. When I was done with the first one I realized a Johnson counter would do the job more nicely. Also, the second digits and characters could be easily derived from the first digit. My first calculator was an HP-15C, as displayed. An easy question for those in the field: what were my second and third HP calculators? Comments and improvement suggestions welcome. Notes: 1) The 47 nF capacitor should be replaced with a 4.7 uF in the real circuit so that the clock frequency is around 1 Hz; 2) The Agilent multimeter is optional :-) ▼ Monte Dalrymple Senior Member Posts: 297 Threads: 25 Joined: Nov 2006 10-17-2011, 04:58 PM 15C, 22S, 48S ? ▼ Gerson W. Barbosa Posting Freak Posts: 2,761 Threads: 100 Joined: Jul 2005 10-17-2011, 05:14 PM Almost: 15C, 2?S, 4?S. Regards, Gerson. ------ When the first digit is 4 the 4017 output O2 is high, low after the inverter, which means the segments "c" and "f" in the second display are not lit. Therefore it cannot display an "8". Edited: 17 Oct 2011, 5:34 p.m. ▼ Paul Berger (Canada) Member Posts: 217 Threads: 4 Joined: Mar 2010 10-17-2011, 05:35 PM 15C 28S 42S ▼ Gerson W. Barbosa Posting Freak Posts: 2,761 Threads: 100 Joined: Jul 2005 10-17-2011, 05:42 PM Yes. It's great it doesn't cycle through 20 or so calculators. But then again I would not pose the problem :-) Monte Dalrymple Senior Member Posts: 297 Threads: 25 Joined: Nov 2006 10-17-2011, 06:16 PM oops. swapped the 2nd and 3rd middle digits. ▼ Gerson W. Barbosa Posting Freak Posts: 2,761 Threads: 100 Joined: Jul 2005 10-17-2011, 06:24 PM Yes, I noticed the swapping later, only after I had already edited my reply to you. bill platt Posting Freak Posts: 2,448 Threads: 90 Joined: Jul 2005 10-17-2011, 07:23 PM Haha and that produced actual models, too, by accident!

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