I understand what you’re saying, and I’m sorry I didn’t ask you ahead of time about the serial port you need to use.
Our C-Series monitors support both RS232 and TTL, you just need to make a few minor changes. The circled position in the picture, position J17, uses RS232 when there is solder, and TTL when there isn’t. You need to change it yourself.
I will send you some articles of our sample project for you to complete your project better, feel free to ask me any questions, keep in touch