How to add a serial port

WARNING attaching a serial port will certainly void your warranty and could destroy your unit.

The following information applies to version B1, there is a version B2 which may or may not be the same. J3 is the serial console connection, some units have a Jameco catalog #420355 connector installed some do not, mine did not. The Jameco catalog number for the plug end is #420267. They are .49” headers.

The serial console at J3 is a logic level signal, not RS232 used by serial ports such as those on PCs. Two approaches have been used to solve this problem. One is to use a USB serial port chip leaveing out it's RS232 converters.

The other is to connect up a 3.3v-to-RS232 converter such as the MAX3232. COMPSys sells an adapter with that I.C. and supporting components on a circuit board with a DB9 connector preassembled, the A232DBH3v (scroll down) which was used in this example.

Using A232DBHv3 adapter

J3 provides 3.3v (pin 1), Transmit Data (pin 2), Receive Data (pin 3) and GND (pin 4), I found that my 25W Weller Soldering Iron would not melt the solder in the GND through-hole so I used a different point for GND.

While it would be possible to wire the A232DBH3v (or other circuit) to the pads, it is better to use a connector so that disassembly remains easy. Since I could not locate properly sized connectors, I used 30ga soild wire such as used for wire wrapping and making board repairs and modifications to install a 2.54mm 4 pin header that mated with a connector I had on hand. This wire is easily inserted into the holes in the J3 pads once the solder is melted. This picture shows the results, not as neat as I'd like.

I then soldered the connector to the A232DBH3v and cut a hole in the back of the unit to mount the DB9 as these pictures show, inside and out.

WARNING if you install the connector backwards you will burn out the A232DBHv3

Using MAX3232 or generic chip

If you want to build your own serial converter, you will need the following parts:

  • (5) 0.1 uF resin dipped capacitors (Monroes), 16V
  • (1) MAX3232 IC (Maxim or generic), 3V type, 16 pin DIL
  • (1) Right angled RS232 male socket
  • (1) 10 element stripboard
  • (1) 16 pin chip mount
  • (1) Wire


J3 Pin Signal
1 Power (+3.3v)
2 Transmit Data (TX)
3 Receive Data (RX)
4 Ground (GND)

Serial Port Settings

Data Settings
Baudrate 9600
Data bits 8
Stop bits 1
Parity None
Flow Control None


Personal Tools