-------------------------------------------------------------------------

+ -
V+ 10v --------->|-----------+
diode \ |
| \| 4
from GPS |3 \
>---------+--------------|+ \
| | 1\------------------> RxD RS232
Z | /
1K Z +------|- /
Z | |2 /
| | | /|11
---- | / ----
/ / / | / / /
ground +-----------------+
Pin 11 |
|
| V+ (Pin 4, +10 v) |
| |
| |
Z \ |
16.4K Z | \ |
(2 x 8.2K) Z 3.3 v |5 \ |
|--------------|+ \ |
Z | 7\--+ 3.3 v
8.2K Z | / |
Z +------|- / |
| | |6 / |
| | | / |
---- | / |
/ / / | |
+------ZZZZZZ-----+
8.2K |
|
+-------------------------+
|
| \
| | \ \
+-----------+--|+ \ | \
+ | |10 \ |12 \
diode V | 8\--ZZZZZZ-------| \ to GPS
- | | / 1 K | | 14\--+--------->
TxD >------ZZZZZZ----+--|- / | | / |
RS232 1K |9 / | | / |
| / | ---|13 / |
/ | | | / |
| | / |
| +-------------+
| |
- | |
--- Z
+ ^ 5.1v Z 8.2K
+ zener Z
| diode |
----- ----
/ / / / / /


Parts List
==========
Qty

1 quad op amplifier, LM324N, Radio Shack 276-1711, $2.99 CDN.
2 diode, 1N4007, or equivalent (not critical)
1 zener diode, 5.1v, 1N4733, Radio Shack 276-565, $1.69 CDN.
5 resistor, 8.2K, 1/4 watt
3 resistor, 1K, 1/4 watt