Can you load an image of the inside of the weight indicator (Yoshua XK3190-A12E)?
I expect it has:
There is another version without the RS232 connector (see bottom edge on right GND, TXD, RXD):
The RS232 version also has extra components on the flip side underneath the first 2 digital segments, probably including a 16-pin MAX3232CSE DIP with it's supporting resistors/caps.
Can the A12E-NoRS232 board generate TTL data? Does it need supporting components? What about VCC?
RS-232 - Wikipedia3-wire and 5-wire RS-232
A minimal "3-wire" RS-232 connection consisting only of transmit data, receive data, and ground, is commonly used when the full facilities of RS-232 are not required. Even a two-wire connection (data and ground) can be used if the data flow is one way (for example, a digital postal scale...)
More on this module at: Read from weighing scale using RS232
Also same issue at Need help with this kind of Rs232