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May 28, 2013
about 2 years ago
It’s just an ordinary lab oscilloscope with its internal screenshot function.
More specifically, one made by Tektronix.
WARNING This board is not stable!
I have experienced so much problem using this board that I had to get a MAX232 to verify whether the problem is with my MCU or the level shifter.
Turns out there’s no problem with my microcontroller at all, it’s this level shifter that’s not doing its job.
Here’s two scope screenshot FYI.
Input / output using MAX232
Input / output using this level shifter
The orange plot is the TX generated from an Arduino, which serves as an input to the MAX232/level shifter in this case.
The green plot is the output from the MAX232/level shifter.
Note that the MAX232 one has a scale of 10V while the level shifter one has 2V.
The expected output is an inverted UART string, at RS232 level (±3~15 volts).
As you can see clearly, the MAX232 gave a nice plot with voltage level at aroud ±9V
This level shifter on the other hand, gave a plot that barely make sense.
I have been stuck on this problem with my project for long enough that I can safely say that I did connect everything correctly.
I even tried to connect the TX-O and RX-I reversely just make sure that I didn’t make a mistake there.
I also understand the fact that this board makes your MCU a DCE (modem), as opposed to a DTE (terminal).
I can confirm that this board is NOT STABLE.
It did “work” a couple of times before, which is the frightening part, because that made me think that there is some other problem in my system.
Maybe some other users used this board with no problem, but I do seriously warn you that this board may get you into serious trouble.
WARNING Use of this level shifter is strongly discouraged to keep you from getting insane.
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