DB9 Serial Expansion Card

I just thought I’d make a thread for my design instead of hogging someone else’s thread and to allow me to update the original post with further information if anything changes.

This is my DB9 (with a female receptacle) RS232 Expansion Card using the FT231X from FTDI, and the SP213 from MaxLinear, I’m selling these for $32USD here, I currently have the first batch of 5 cards assembled, they just need enclosures which I am still in the process of prototyping, which will be ready to go once the courier opens after Easter, and I will be making a couple more batches, I will keep on ordering batches as long as people are interested.

GitHub repo


I’ve placed the assembly order for 50 units, which should arrive in 7-21 days.

What do people think of just the payment link, compared to a Tindie or a Lectronz store page as I could setup a store page for one of those platforms?

I just received my DB9 expansion card. I’m really surprised you went with a female DB9 - AFAIK the convention is for male on the computer (DTE) end of RS232 links. Do you think there’s a male connector with the same footprint I could swap onto my board?

K31X-E9P-N is the male variant of the connector in the design.

You will need to do a fair amount of pin swapping to fit the opposite gender connector, so that the pinout is correct for signal direction.

Also which connector do you call a male connector? The correct designation is that the connector with male pins is a female connector because the body of the mating connector goes inside the body of this connector. People often call the connector with male pins a male connector, but then get confused when pointed to manufacturers literature that shows that as a female connector, so I have got into the habit of referring to male and female pins when talking about these connectors.

Ack, that’s true. That sounds like it’s too much trouble to be worth it. :frowning:

I’ve never heard someone call the connector with pins a “female connector”. Wikipedia matches the nomenclature I’m used to - “parts with pin contacts are called male connectors or plugs , while those with socket contacts are called female connectors or sockets”.

AIUI the convention for DTEs (and thus computers) is to have the connector with male pins on the computer, use a male-female cable, and the connector with female sockets on the DCE. You can see this in the photo Wikipedia has of a serial + parallel expansion card (note that the convention for parallel ports is reversed).

This appears to match manufacturer naming AFAICT. Hirose calls the version with pins a “male” connector. I noticed that Kycon avoids the issue by calling them Pin or Socket. :slight_smile:

That is correct when the pins are proud of the connector body, such as a mains plug. But the D series connectors have a shroud over the pins which is what makes them the female half of the connector pair. I have seen this described on several different manufacturers data sheets for D connectors so often, but can understand why people get confused. The gender of the connector is formed by the body shell, not the pins.

Unfortunately the description in the Wikipedia article has tended to become the commonly accepted usage. I didn’t believe it either until it was pointed out to me on manufacturers data sheets in the 1980s.

Actually the correct naming is ‘plug’ and ‘receptacle’ as this data sheet has it.