INSTRUCTONS FOR THE HP48SX IR DECODER

1) The circuit diagram is attacted to this message, as a printable ASCII TTYpic. I should be printable on _any_ printer.
2) Construction and layout is not critical and any metohd should work. I used Verowire self-fluxing wiring system. I also socketed all the IC's, but that too is up to you!
3) De-coupling capacitors and power connections are not shown on the circuit diagram. Place a 0.1uF ceramic capacitor across the power connections on each IC. Also place a 10uF tantalum capacitor across the power connections close to the IR transmitter.
4) The IR LED and IR phototransistor should be mounted on the front panel of the unit. The LED goes on the Left, looking at it from outside. They must line up with the ones on you HP48 for transmission to occur at all. The range of the unit is about 2".
5) The IR LED and phototransistor are critical. I used ones available from MAPLIN (see my earlier messages for the address), but the equivalents are: Phototransistor Maplin YY66W (Infra Red Sensor) = TIL78 LED Maplin YH70M (Infre-Red Emitter) = TIL38
6) The RS232 port links to the PC, not to the HP48 of course.
7) The circuit as given requires a +5V supply only. The MAX232 device (which is expensive and hard to obtain) can be replaced by a 1488 (transmitter) and 1489 (receiver) devices but then +/-12V are required for the 1488
8) Each section of multiple ic's is numbered. 'xx means 74lsxx. A total list of ic's required is: MAX232, 2*74ls393, 7425 (or 74ls25 if you can get one!), 74ls74, 74ls08, 74ls14 74ls04.
9) A list of symbols used is: (as some are non-standard to get them into printable ascii)

-\/\/-- resistor ! \ / \ resistor / ! !! --!!-- capacitor !! !--! +! !+ -!! !!- Quartz Crystal +! !+ !--! !/ ! NPN transistor !\! - \\ >> ! / !/ !\ IR phototransistor ! \! - ! >> V// --- IR LED ! !\ -! >o- NOT gate !/ -!\ ! )- AND gate -!/ -) ) -)--\ ) >o-- NOR gate -)--/ ) -) Good Luck! I am on ARD@UK.AC.BRIS.SIVA (JANET) = internet ARD@siva.bris.ac.uk +5 ---- ! ----------------------------- ! ! ! / ! ----+ o '74 \ 10k '04 ! '04 '04 '08 /// ! --------- \\ / !\ !\ ! !\ !\ +-!D S ! >> !--------! >o---+--! >o-+-! >o--! >o--!\ ! Q! ! / !/ ! !/ !/ !/ ! )-+ ! !o------+ !/ IR 74ls14 ----------------------!/ ! +- !> R ! ! !\ P/transistor ! ! --------- ! !_\! ! ! o +5 ! ! ---------------------------- ! ! ---- ! ! ! ! ! ! ! --- ! ! ----- ! /// ! ! ! '393 ! '14 ! ! ---------- !\ ! ! ! R ! +- ! >o-+ '25 ! ! ! A!-+ !/ +-----) ! ! ! ! ) +---+ ! ! B!---------------)--\ !\ ! ! +---!> ! ) >o--! >o--+ ! ! ! C!---------------)--/ !/ ! ! ! ! ) '14 ! ! ! D!---------------) ! ! --------- ! +-----------------------------------------------------+ ! '393 '393 ! ! 2.45MHz !----! !----! ! ! '04 !--! '04 '04 ! A! ! A! ! ! !\ +! !+ !\ !\ ! B! ! B!--+ ! ----! >o-+-!! !!--+---! >o-----!--! >o---!> C! +-!> C! ! ! ! !/ ! +! !+ ! !/ ! !/ !R D!-+ !R D! ! ! ! ! !--! ! ! !----! !----! ! ! ! 1k ! ! 1k ! ! ! ! ! -/\/\----+ 2n2 --/\/\-------! --- --- ! ! ! ! ! ! /// /// ! ! ------------! !-----------------+ ! ! ! ! ! ! +5 ! ! ---- !! !! 4*22u ! ! ! +-!!-+ +-!!-+ ! ! ! ! !! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ------------------- ! ! ! ! C1 C2 ! +---------------------------------)---+ +----!Vcc ! ! ! --- ! ! ! ! +5 ---+ ! ! ! ! ---- +----!+10v ! ! ! ! >> ! ! ! +-----------------------------+ V // PC ! ! ! ! '393 --- RS232 ! ! ! ! !----! ! IR >-----!TxO1 TxI1!--+ ! ! A! +-/\/\---+ LED Tx ! ! ! ! B! 2N3904 ! 56R !TxO2 TxI2! +---!> C! !/ ! ! +-------!R D!----/\/\----! >-----!RxI1 RxO1!--+ !----! 1k2 !\! Rx ! ! - ! !RxI2 RxO2! ! ! ! --- >--+ ! -10V Gnd ! /// Sg ! ------------------- ! ! !! ! ! +--!!--+ ! !! ! --- + ! /// ! --- ///

HP IR FORMAT BELOW

Taken from ioguide.doc, ftp from ftp hpcvbbs.cv.hp.com, dir pub

The IR port allows half-duplex communication between systems at 2400 baud using pulses of infrared light instead of wires. Full-duplex is not used due to the need to suppress reflections. The format for IR transmission is similar to serial transmission except that a pulse of infrared light of 52 Ns duration (nominal) is used to transmit a zero-bit. The absence of a pulse indicates a one-bit or idle condition. Note that if the pulses are stretched out to fill a bit time this becomes very similar to the serial signal.