From: ard@pva.bristol.ac.uk (Tony Duell)
Newsgroups: comp.sys.handhelds
Subject: HP48 to RS232 link
Keywords: HP48 RS232
Date: 30 Aug 90 11:29:24 GMT
Reply-To: ard@pva.bristol.ac.uk (Tony Duell)
Organization: Public access to Usenet in the UK

I have received many request for the circuit of my HP48 to RS232 decoder/
Infra-RED link. I have converted the circuit diagram to a printable ascii
file, writen some instructions, and I'll include them in this posting.
Please contact me if you have any problems - stuff sent to the net takes
a few days to find me......

Here it is:

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.PVA (JANET) = Bitnet ARD@pva.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*2u2                                  !   !
   !     +-!!-+    +-!!-+                                      !   !
   !     ! !! !    ! !! !                                      !   !
   !     !    !    !    !                                      !   !
   !    -------------------                                    !   !
   !    !  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  !  -------------------
     !       !  !!  !
     !       +--!!--+
     !          !!  !
    ---          +  !
    ///             !
                   ---
                   ///


Good luck with the construction.......
Tony Duell, H.H.Wills Physics Lab, University of Bristol, Tyndall Avenue,
Bristol, England.
JANET   : ARD@UK.AC.BRIS.PVA
INTERNET: ARD@PVA.BRIS.AC.UK

Newsgroups: comp.sys.hp48