LVTTL to RS-232 converter revisited

I recently posted a query about an RS-232 to LVTTL converter circuit.
Thanks to all who replied. I built the circuit and it seems to work fine.
The rising edge is a bit leisurely. The falling edge is pretty fast.

For reference, here is the actual circuit I ended up building. (Use
courier or other constant-width font for ASCII art schematic):

VCC (5V)
|
/
\ R2 (1k)
/
|
+----------------+-> to LVTTL device
| |
R1 (10k) /c /
RS-232->---/\/\/\/\--+----| Q1(mmbt2222a) \ R3 (1k)
| \e /
/e | |
D1(mmbt2222a) +--| | /
| \c | \ R4 (1k)
| | | /
+---+--+--+ |
| |
GND GND


As you can see, D1 is a diode-connected transistor. I did this because we
have lots of mmbt2222a's, and no SMT diodes in stock.

--Mac

.

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