One problem here, the HP's receiver circuitry is limited to only a couple
of inches, i guess to keep people from cheeting on tests, The transmit
range, however, is much farther, In fact i can use my hp to turn on my tv
from accross the room (more than 10ft). Also, the signals are inverted,
that is, no IR light means 1 while IR light means 0. Hope this helps. (I
myself am planning on interfacing my HP to a MCU using its IR
capabilities, but i havent tried anything yet.)

------------------------------------------------------------------------------
A member of the PI-100 Club:
3.1415926535897932384626433832795028841971693993751
058209749445923078164062862089986280348253421170679

On Tue, 1 Dec 1998 MattBeck@AOL.COM wrote:

> Not sure of the other methods used, but I know the HP48 series is half duplex
> serial com. It is software timed, the acutal IR led, and IR phototransistor
> are memory mapped. There is no modulation or demodulation to worry about but
> range is limited to about 12". Just use a phototransistor to read and a IR led
> to write to the Hp48 using normal (8,N,1) serial com. (2400baud max). Matt
>