Converting Ethernet to RS232 converter to TTL
The USR-TCP232-302 is an inexpensive little box that basically gives you a RS232 port that can be accessed over TCP.
Since TCP is a stream-based protocol, this works nicely — just send data to the embedded TCP server in the box, and it comes out of the RS232 port; any data received by the RS232 port gets sent back to the TCP client. In fact, the embedded software on the device has a few other options, including acting as a TCP client and connecting to a TCP server of your choosing, or similar modes with UDP.
But who uses RS232 in this day and age? We’ve all got TTL serial ports. Fortunately, neither does most of the chips that drive this little device. In fact it has a SIPEX3232 chip specifically to handle conversion from TTL levels to RS232 levels.
Double-fortunately, the makers have been kind enough to provide unpopulated header spots for not only the TTL level (3.3V) RX and TX pins, but also a 3.3V supply. It’s a simple case of wiring into these, and disconnecting the SIPEX3232’s R2OUT pin which is holding the RX high.
The SIPEX3232’s R2OUT is actively driving the pin. Unfortunately it’s a SP3232E rather than one of the larger models which have !EN pins that we could have tied to ground to disable the chip (high-Z output). So we just have to lift up the pin. I de-soldered the unused DB9 for convenience.
Once the SP3232E’s output is disconnected, you now have a direct 3.3V TTL connection to the on-board micro. I don’t know if it’s 5V tolerant, I opted not to find out; because there was a handy 3.3V supply, I soldered in a level shifter. The result is a nice little box that frees you from the grief of having to use USB-serial for everything.
For example, here’s a GRBL CNC controller running over the network:
