Arduino NG to DB9 serial

oddly enough, I bought an Arduino NG because i had no DB9 serial on my new computer, however, now I need to use it on a computer that lacks USB...

can someone explain what pins on a DB9 would go to what ports on Arduino?

is it just:

rx to rx tx to tx +5v to +5v ground to ground

or is there more to it?


if you mean that you want to connect the DB9 serial port pins to the Arduino NG's headers, then there is more to it.

The DB9 version had some transistors to do RS232-TTL level conversion. You'll need some kind of level conversion... you could use a MAX232, which is a common chip. Not sure if the polarities will be right, but it is a start. Alternatively you could build the RS232 version form the schematic on the Arduino main site.


The easiest way is probably getting an internal USB-PCI card for that computer.

TX to RX, RX to TX, ground to signal ground, but you must do voltage and level translation. RS232 uses different voltages and levels than TTL.

Fairly easy way: build a circuit with a MAX232 and 5 caps, connect the arduino tx, rx, gnd, and +5 (to power the MAX232), add a DB9.

Easier way: build a circuit with a MAX233 which doesn't even need the caps (but the 233 is more expensive than the 232).

Cheapest way: build a circuit with some transistors and other components to steal voltage levels from the host 232 port and invert the levels for you. The Arduino serial does this, check the schematic for details.

Easiest way: buy an Arduino serial.


well, i’m working on the rs232 method shown at, but until i find a local (read: in vermont, the great non-electronic wasteland) source for the max3323 chip i’m stuck… i figure i’ll add a usb pcmcia card, but I can’t remember if its 98se on the notebook or 98, if the latter, I wont be able to get usb, as the cd is dead, and there’s no floppy, so upping the OS would be hard.


Maxim, makers of the all kinds of interface chips including the ones above, are kind enough to provide a sample service... for (a few) chips, go to and register. Once you do this, you will be able to request up to three free samples per device type, through their automated sample system. Only drawback is that it is slow-- sometimes take a couple of weeks as the parts often come from Malaysia.

Digikey will also sell them to you via mail or UPS.


PS: non-electronic wasteland = unspoiled nature = good thing, or at least it used to be. :)

definitely nice living here, especially in the fall and winter, but there are drawbacks, such as lack of ECE jobs and difficulty of getting parts without ordering.

still, you can see which side i lean toward, as I still live here.

btw, placed a sample request... thanks for the info