Here are some more options for getting an old 1980s computer on the internet via RS-232 to WiFi/Ethernet adapters.
The ESP8266 developer modules, like the one I picked up from Amazon for $8.99, are available for around $2.75 when shipped from China. That, and an RS232 converter for about .67, is about all you need other than some wires to connect stuff up, and a USB power supply. See AliExpress.com for options. There are also e-Bay sellers that have similar prices.
The advantage this module has is tons of third party firmware. There is the ZIMODEM project that makes the module look like an old Hayes smartmodem. You can use “AT” commands do dial (IP address instead of phone number) and even answer a call (incoming telnet connections appear as “RING” and “CONNECT” just like someone calling in to a modem BBS).
This part is also used for RS232 to WiFi and Ethernet conversions. You can find a board that this part plugs in to for about $4. Here is one from e-Bay:
The board accepts a 5V power supply, then has an RS232 DB9 connector on one side, and two Ethernet ports (LAN and WAN) on the other. When the HLK-RM04 is plugged in, that makes it work, and also provides WiFi.
The module is available with internal or external antenna. You can buy one with everything you need (no case) for about $13! Here is an example at AliExpress:
The disadvantage of something like this is that it’s just raw TCP or UDP communication. This means if you want to do real Telnet, you have to write some code to parse the data and handle telnet protocol. You would also have to implement any other protocols in code, while smart firmware would be written on the ESP8266 (and probably already has!) that goes things like HTTP GET, mail fetch, etc.
More to come…