https://redd.it/d09nrz

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The people on that site don't seem to know much about RS-232. I work with it on a daily basis. There are 9 pins in the standard, but really all you need is 3 for most purposes. 5 are used in some applications. Signals most likely used here and their DE9 pin assignments: 2: Tx 3: Rx 5: Ground 7: RTS 8: CTS Edit: I almost forgot the best part: Tx is wired to Rx, and RTS to CTS, and vice versa. The pins cross. Often, on schematics, the designers forget to note whether that wire that says Tx is Tx from the other side, or Tx from their side, so you will likely have to use a scope to figure out the data traffic directions. You can't rely on the schematics. I have more than a few custom cables I've build with splices in the middle. If it's really RS-232, then the logic levels of the data pins will be at -5V most likely. It can go to -15, but that's rare these days. It'll switch to +5V on a logic 0. If it's TTL logic, then the voltages will all be either 0V or 5V. If it's TTL, they make TTL-RS-232 adapters as project boards at places like spark fun, which you can then wire into an RS-232-USB adapter. My company has a custom cable built for one of our products that does this. Computers used to have RS-232 ports all the time, but you have to get a separate RS-232-USB adapter these days. I exclusively use MOXA, because they are the best, but they are pricey. You might be able to find a cheap adapter. You'll have to wire the correct pins from the 5 pin to a female DE-9 connector, that matches the male DE-9 connector that a USB-RS-232 adapter will have. Once you get it wired correctly, you'll then need a terminal program (such as PuTTY or Terra Term), and to know the correct baud and other settings to connect. You will also have to know the correct command syntax for the device you are talking to. This part alone will probably keep you busy for quite a while. More on reddit.com

This pinout worked for me: RJ45 -> DB9 RTS 1 -> 8 CTS DTR 2 -> 6 DSR TXD 3 -> 2 RXD GND 4 -> 5 GND GND 5 -> 5 GND RXD 6 -> 3 TXD DSR 7 -> 4 DTR CTS 8 -> 7 RTS IIRC, I had to leave one of the ground pins unplugged. http://i.imgur.com/O3RRKQC.jpg *Edit: Here's another picture for clarity. Also, you can push the pins back out with something like a small flathead screwdriver (~1mm). http://i.imgur.com/7hWniXb.jpg More on reddit.com

Two of those blue cables, coupled together, will give you a straight-through serial cable. the biggest problem that I see is that a DB-9 connector has 9-pins and an rj45 only has 8 contacts. Does the missing pin not matter? The missing connections only matter for a modem. More on reddit.com