Question: I want to make the same signal like the following images using an Arduino Uno. But I can't find the baudrate of this signal.

I calculated baudrate the same way as Wikipedia. But when I used the baudrate I got framing error.

The duration of the start bit: 0.2223 ms

1/ ( 0.2233 / 1000) = 4478 bit/s

What did I do wrong?

[![Enter image description here](https://i.stack.imgur.com/i9GSz.png)](https://i.stack.imgur.com/i9GSz.png)

Update
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The device has the following 4 pins.

* VIN: 12 V
* GND
* GND
* SIGNAL: 3.3 V

I don't have any documents like a datasheet or a manual. I think that it uses UART communication because there is only one signal pin.

I upload the logicdata file on my Dropbox account: [Here](https://www.dropbox.com/s/6lzz95954ve3rzm/12%20MHz%2C%2012%20M%20Samples%20%5B8%5D.logicdata?dl=0)!

Answer: 
Try 10500 baud. The data stream should be `0xAA 0x24 0x00 0x00 0x55`. My suggestion to determine the baud rate is to look for characteristic bytes. In your capture the long zero sequence is a good candidate (generally, the `0x00` and `0xFF` bytes look very characteristic on serial):
[![enter image description here](https://i.stack.imgur.com/QAxPt.png)](https://i.stack.imgur.com/QAxPt.png)
10 bits divided by the total length of the marked box gives you the baud rate.
I believe the baud rate is 14400.  

[![enter image description here](https://i.stack.imgur.com/DMnqC.png)](https://i.stack.imgur.com/DMnqC.png)  

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I estimate (measured with ruler) the yellow pulse is about 3.2x the green pulse.  

**I multiply your 4478 bit/s by 3.2 = 14,329 bits/s.**