prindle@nadc (04/03/86)
From: prindle@NADC
I found it!
Here is the schematic for the interface I've used for several years. Of course,
there is a new chip available from Maxim Integrated Products called the
MAX232 which will produce true +/- 10V RS-232 from a +5V supply and TTL inputs,
but you won't be able to waltz into your Radio Shack and get one for a year or
so anyway, so......
(Incidentally, this will fit on a 1 inch square PC board)
Frank Prindle
Prindle@NADC.arpa
--------------------------------------------------------------------------------
Commodore 64 to RS-232 Modem Interface (if modem will accept TTL levels)
------------------------------------------------------------------------
User Port Pin Modem Pin (DB-25)
------------- -----------------
+5V 2>-------->+5V
+5V
^
2K |
-----/\/\/\-------------
| | -------------------------<2 BA Xmit
| 10K |<--- | Data
XMIT M>--------/\/\/\--------| | 1K
DATA |-----------/\/\/\---
2N2907A (PNP) |
|
-----
^ -
5K |
------/\/\/\---
|
| 2N2222A (NPN)
RECV B>---------------| 5K
DATA | |------------------/\/\/\---------------<3 BB Recv.
C>---- ----<-| | Data
| | |
|--------->|-----
| |
----- AOD (Any Old Diode)
---
-
GND N>-------------------------------------------------------<7 AB Signal
| Ground
-----
---
-
Note: This circuit is not particularly sensitive to transistor type - almost
anything should work at this speed - the types given are representative
of their type and should be available at Radio Shack.