Reverse engineering baud rate on raw, single wire, half duplex serial communication.

Hello everyone,

I am new to electronics, so please forgive me if my terminology is poor.

I am trying to reverse engineer a serial connection on an LCD toy. The connection itself is two pins, and I know one of them is connected to ground - leading me to deduce that it must be half duplex communication on the remaining pin.

I wrote a sketch on arduino to open a serial connection on a digital pin and monitor it via the IDEs built in serial monitor. After some tinkering, I was able to log some data. The problem I am running into is that the data logged does not appear to be consistent, and I believe it is due to my baud rate being incorrect.

No matter what I select for baud rate, the pattern is largely the same: incoming bits are low (0) when communication functions on the toy are disabled, when I enable them the incoming bits go high (1), and when I begin transmitting it seems to go low for a brief hold period, then sends a series of bits, then goes back to being high.

My question is, is there any way to reverse engineer what baud rate the device is communicating with? And a follow up, without knowing the protocol used to communicate, is there anyway way to be fairly sure you have found the correct baud?

For example, there is a communication function in the toy that should be sending the same data every time. Right now I cannot get that capture to consistently dump the same data. I imagine if I found a baud rate that resulted in this data being consistent, I may have found the correct baud?