S7-300 PLC with RS232 and stepper control
I built this Siemens S7-300 PLC lab with various hardware I had around the shop and cheap items from eBay - most S7-300 is cheap on this year of 2022. The logic I wrote does two tasks simultaneously: read an analog channel voltage and then transmit it over RS232 in ASCII format when any character is sent to the PLC - pressing enter on Hyperterminal or PuTTY will make the PLC to reply with "Channel (1) = 1.205677" for example. And the second task is to control a stepper motor - home it upon start up, and then control the direction depending on a target pulse count.