I am an electrical engineering senior student and I think I tried everything. Here is the case: (no i am not using the USB to RS232 convertors)
I bought a digital scale that can send the weight serially to a machine. When you request the data by sending W (57 in hex) the scale sends back the weight. As I always do, I try to narrow down the culprits so I tried the following:
1) I created an RS232 connector using MAX232 and a raspberry pi and was able to send through Minicom (like putty) a W and receive a weight value.
2) I used the same circuit to connect the Raspberry Pi to my Windows machine and successfully communicated back and forth with Putty.
Simple right? I mean UART, it should be.
So the cable is fine, the scale works as advertised, putty on windows works, the the ports on the windows machine work; however, the Windows machine and the scale refuse to communicate. Which means that the W is not reaching the scale because I am not getting back anything, not even junk.
3) I also tried steps 1 and 2 with a virtual machine running win 7 instead of Win 10, and even tried a usb to rs232 cable that I know is functional...works with rpi but not with the scale.
I have only one last explanation. In my building we do not have Grounding in the plugs. All appliances work fine, but they will give you a neat zap if you touch them bare foot. What this has to do with the problem is that I think the (rpi+max232+DC power supply) system is well grounded while the PC (not grounded) to scale (not grounded) system is suffering from a noise issue. Can this be the case? Do you have any other suggestions that I could try? (I called my grandma asking for some holy water) Thank you in advance.