Use of empty space in Prizm

[SimonLothar]

I was thinking about removing the db9 connector and soldering a 3pin female (connected to Rx, Tx and Gnd).

I think you have to remove the MAX233, too. Otherwise the MAX233's TTL-IO-lines would compete against the calculator's.

...because it needs 3,3V (and it is also very large).

The TTL-specifications are: low:<=0.8V and high:>=2V.
As the PIC can be interfaced by a MAX233, its signal levels are obviously TTL.
2.8V and 3.3V should make no difference concerning the signal-level.

[Arkhs Profile]

Thanks for the info.