Use a logic analyzer and record the signal. One of these cheap 24MHz/8C USB probes off ebay or Amazon plus a level shifter will do it.
The software for these logic analyzers can decode UARTs. This will prove that the data sent is correct both in data as well as in timing. You can measure the length of a bit and calculate the resulting bit rate from it.
If the data sent is correct it must be the receiving end. USB-serial adapters either have a crystal or get the base operating frequency from the USB SOF signal. The crystals are mechanical devices that can break, and they will change frequency depending on temperature. Try a different adapter.
And - and I repeat myself - use a Pi4/5 and one of the many internal UARTs. This skips many parts that can go wrong. And a Pi4 is not that expensive especially given the commercial application.
The software for these logic analyzers can decode UARTs. This will prove that the data sent is correct both in data as well as in timing. You can measure the length of a bit and calculate the resulting bit rate from it.
If the data sent is correct it must be the receiving end. USB-serial adapters either have a crystal or get the base operating frequency from the USB SOF signal. The crystals are mechanical devices that can break, and they will change frequency depending on temperature. Try a different adapter.
And - and I repeat myself - use a Pi4/5 and one of the many internal UARTs. This skips many parts that can go wrong. And a Pi4 is not that expensive especially given the commercial application.
Statistics: Posted by fchk — Wed Sep 24, 2025 8:20 am