HP-42s double speed modification and printing

[Bernd Grubert]

Hi,
I'm thinking about making the double speed modification described here. I wonder whether the ir-printing is still working after the modification. Has anybody tried this?

Regards
Bernd

[ijabbott]

(11-03-2020 09:27 PM)Bernd Grubert Wrote:  I'm thinking about making the double speed modification described here. I wonder whether the ir-printing is still working after the modification. Has anybody tried this?

Perhaps it will print twice as fast. :-)

[Bernd Grubert]

Good point!
May be you're right

[Valentin Albillo]

(11-05-2020 08:48 PM)Bernd Grubert Wrote:  Good point!
May be you're right

I doubt it. The "HP-42S Owner's Manual" p.103 says:

"Since the HP-42S is capable of sending information faster than it can be printed by the HP 82240A infrared printer, the calculator uses a delay time to avoid losing information."

and that's at normal speed, let alone 2x.

V.

[Bernd Grubert]

(11-06-2020 01:15 AM)Valentin Albillo Wrote:  "Since the HP-42S is capable of sending information faster than it can be printed by the HP 82240A infrared printer, the calculator uses a delay time to avoid losing information."

You're right. The mechanics of the printer are the bottle neck. But with the Redeye-Interface project from Martin and Meindert it should really print at double speed. But actually that was was not my reason for the modification. I just wanted to increase the calculation speed.

In the meanwhile I exchanged the crystal. Unfortunately the printer doesn't work at all . I'm afraid the timing is too fast now. Same holds for the RedEye Interface. Here it might be possible to adapt the software of the Arduino board to the faster timing.

Regards
Bernd

[Diego Diaz]

Hi Bernd,

The IR signal is in fact a modulated series of pulses. A carrier is switched ON/OFF according to the transmitted data.

The receiver detects (and then filters out) that carrier, extracting the data pulses and passing them to the printer mechanism.

Since the carrier frequency depends on the HP-42S clock it can no loger be detected at 2x and hence the printer won't work at all.

That's why all my 2x mods to 42S inlcude a switch to revert it temporarily to the original speed when printing.

Hope you find this info useful.

Best wishes.

Diego.

[Bernd Grubert]

Hello Diego,

(11-09-2020 11:31 PM)Diego Diaz Wrote:  That's why all my 2x mods to 42S inlcude a switch to revert it temporarily to the original speed when printing.

Thanks for the tip with the switch. Where and how did you insert it in the calculator?

Furthermore I found a way to print to the Redeye-Interface project in double speed. I just had to change a counter value in the arduino souce code (see attached patch).

Regards
Bernd


  doublespeed_patch.txt (Size: 475 bytes / Downloads: 7)

[Diego Diaz]

Hi,

Here you are.

   

A piece of double sided foam tape (not shown) is required under the Xtals. before reassembly.

Cheers.

Diego.

[Bernd Grubert]

Thanks for the photographs, Diego.
I may give it a try.

Regards
Bernd