Serial adapter for 3.3V TTL
This document describes how to build a converter from 3.3V TTL levels to RS232, which allows interfacing to a standard PC 9-pin D-sub port.
To build the serial adapter you will need the following parts:
- 1 x piece of solderable breadboard, predrilled with standard 0.1" spacing
- 1 x MAX3232 dual driver/receiver
- 1 x 16 pin DIL socket (optional)
- 5 x 0.1uF/10V polarized capacitors
- 1 x 9 pin D-SUB male connector
- up to four connectors for the serial header in your NAS box
- some wire
In this description I am using a board where stripes of three holes are connected with copper. To connect to the NAS serial port I have glued together two header plugs with three holes each, forming a connector for a 2x3 serial header, suitable for Synology and QNAP. Depending on the kind of serial header in your NAS box you will have to build a suitable plug.
This is the converter circuit we have to build, drawn using
gschem
from the
gEDA suite.
-
J1
is the plug for the serial header. Pin 1 is 3.3V, pin 2 isGND
, pin 4 isTX
. and pin 6 isRX
. Adapt this to your NAS as required. -
U1
is the MAX3232. Note that pin 15 (GND
) and pin 16 (VCC
, 3.3V) are not visible, but have to be connected nevertheless. -
CONN1
is the male D-SUB interface with 9 pins, where pin 2 isRX
, pin 3 isTX
and pin 5 isGND
. -
The five capacitors are called
C1
toC5
.
The following picture shows the soldering side of the board, to give you an idea how to place the components and which copper stripes have to be connected.
- Red: The positions of the five polarized capacitors. Watch their polarity!
- Green: The arrows show which copper stripes have to be connected. You can do that either with small wires on the component side or with a soldering bridge on this side.
-
Violet: A short wire on the component side to
connect pin 2 of
U1
with the positive side ofC1
. -
Blue: A longer wire on the component side to
connect
C2
atU1
pin 6 withGND
. -
Yellow: Here you will solder seven long wires.
Three of them (
2 RS232
,3 RS232
andGND
) connect to the D-SUB RS232 interface while the other four are for the serial header in the NAS. Note that one hole (labeledGND
) is used for both and gets two wires.
This is how the component side of the finished serial adapter looks like:
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