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Today I received my HP-30B and also the keyboard overlays. (Thanks Eric!) The cable seems to take a little longer to get here though. So I thought I'd have a look inside the calculater and maybe just connect the RS232 myself (yes, I am a bit impatient). I assume all I need is levelshifting to 3.3V on the RXD and TXD line. But so far I haven't even managed to open the calculator. I have unscrewed the 5 bolts but still can't figure out what to do next. Could someone enlighten me please?


Pry it apart from the side by slightly bending the grey (softer) plastic.

Get yourself an FTDI RS232-TTL 3V3 cable. You can wire it directly to the pads. You will need a way to connect the erase pin to Vdd in order to activate the SAM-BA boot loader (by clearing the flash completely). Reset is available through a hole on the back.

Thanks Marcus, that worked. Got it open now.
While I have it open, is it worth adding a crystal? Does that help with any functionality other than communication (I probably won't need that, so I am not too bothered)?
I like your idea of adding a 3.5mm connector to the calculator, but unfortunately can't work out a solution that is a bit easier on the eye ;)


Edited: 26 Feb 2012, 8:11 a.m. after one or more responses were posted

Adding a crystal helps a lot with communication and with the STOPWATCH function. If you don't use them, don't bother. Soldering the capacitors is not obvious.

A stopwatch sounds like a nice feature to have. So I think I will do the modification. Soldering the caps is no problem. After all they are the large 0603s and not 0402s ;) The crystal seems to be more of a problem - I haven't got one and need to order one -> more waiting :(


I think I figured out how to connect everything appart from the "Erase" button.
I belive the pinout on the flash connector to be:

J31: Vcc (3V)

J32: reset

J33: TxD

J34: RxD

J35: GND

J36: erase???

Is that correct so far? Does the "erase" button pull up J36 to Vcc like "reset" pulls up J32?

I bet the cable arrives by the time I worked all this out...


Erase needs to be pulled high to do an erase. The calculator needs to run for this to work. Just press the ON key to wake it up with ERASE pulled high. (I had accidentally written Vdd which is wrong.)

The SDK mentioned here contains schematics.