Wednesday, April 13, 2016

A VFD module for the calculator?

One of the problems with converting a stock calculator to emulate a Busicom 141-PF is that most calculators these days max out at 12 digits, while the 141-PF was a 15-digit calculator. The example Tim McNerney gives in his PIC-based printer emulator test data is:
//                   111111 1 1
//          123456789012345 7 8
/* ============================= */
/*          3.1415926535897 x    */
/*                        2 =    */
/*          6.2831853071794   *  */
/*                               */
/*                     -456 /    */
/*                     2.37 =    */
/*         -192.40506329113   *  */
/*                               */
/* ============================= */
Thus it's not as simple as dropping a couple of digits to truncate the output to 12 digits. Nor would that account for the two special characters that appear in columns 17 and 18. One way I'm considering handling this is to replace the P170-DH's fluorescent display with an LCD module.

One I'm considering is the CFAH2002A-TMI-JT module from Crystalfontz, a company I've bought from before. This module is a negative transmissive LCD with a blue foreground and white LED backlit characters. This is important because the P170-DH has a blue-colored plastic bezel, and I think this combination is most easily viewable compared to a the typical yellow-green transflective display. It displays two lines of 20 characters each, so I could either show the last two lines printed or display status on the second line. It's fairly inexpensive at about $15, but presents some mounting challenges.

Still, the idea of using a Vacuum Fluorescent Display module has stuck in my head. Most of the VFDs I've found haven't been suitable, but I just came across the DS2029H from Noritake-Itron. Not only does this module appear to be an almost perfect fit for the P170-DH, it's less than $30 in sample quantities from the manufacturer.

Of course VFDs require some strange power supplies (+5Vdc and +35Vdc in this case) but that's manageable. This module includes a controller that looks much the same as those found in LCD modules so I don't need to deal with segment drivers and the like. They also sell VFD modules that look just like LCD modules (including one they're discontinuing that is being sold at only $18), but like the LCD modules they wouldn't fit as well.

Edited to add: I ordered a DS2029H Vacuum Fluorescent Display from Noritake-Itron Wednesday. It just shipped, so I should have something to play with next week.

No comments:

Post a Comment