Here it is: the MAX203 TTL to 232 converter. It is very easy to build.
You only need the MAX203 ic and some wire.


               MAX203


                +5 Volt input
                  |
            ______|7____
        -- |            | --
       | 2-----conv-->----5 |
TTL in |   |            |   | RS-232 out
       | 1-----conv-->----18|
        -- |    	| --
           |            |
        -- |            | --
       | 3---<-conv-------4 |
TTL out|   |            |   | RS-232 in
       | 20--<-conv-------19|
        -- |            | --
           |            |
 12 (10) __|            |___ 11 (12)
        |  |            |   |
     17 |__|            |___| 15
           |            |
           |            |___ 16
           |            |   |
           |            |___| 10 (11)
           |____________|
             6|     |9
              |_____|
                 |
                GND

These are connections for the DIP (SO) package
Pin numbers in ( ) are for SO package (SO=Small outline = SMD)

e.g. if you have the DIP version you must connect pin 12 with 17,
11 with 15 and 16 with 10. But if you have the SO version you must connect 
pin 10 instead of 12 with pin 17, 12 with 15 and 16 with 11. Pay 
attention to that!

You can use ttl and 232 input and output as you like, but notice that ttl 
input on pin 2 corresponds to 232 output on pin 5, ttl in on pin 1 
corresponds to 232 out on pin 18, 232 input on pin 4 corresponds to ttl 
out on pin 3, 232 input on pin 19 corresponds to ttl out on pin 20.

The +5V input should probably be regulated. You can use a LM7805 to do 
that. I hope you have a source for this IC. Or you can buy an IC regulated 
voltage transformer for $6 or $7 (in Italy £15000) and use it. I use one 
with output set at 4.5 volts.

I built a videocrypt card, the 1341 interface and Casio SF Digital Diary 
series using this ic and it works fine.