Wednesday, November 26, 2014

Trying out a mini logic analyzer

I just got a small and inexpensive logic analyzer from dx.com. Basically, it contains a CY7C68013A microcontroller and 74HC245 buffer chip, and you can upload firmware which makes it into a logic analyzer.

I used sigrok PulseView. First I tried it in Windows. It's easy to install the driver using the included Zadig executable. After that, PulseView tended to crash on startup if the logic analyzer was connected. I only got it to run a few times. Also, it seemed to lock up sometimes when capturing for a second or third time. I expect this is due to bugs in the Windows version of PulseView, and not due to a problem with the hardware.

Here's a decode of a NEC protocol IR remote. I couldn't get it to work at the default 20 kHz sample rate, even though that should have been fast enough. It worked at 100 kHz.
Here's some 9600 baud serial communication. This is also at 100 kHz. It also worked at 20 kHz sampling if I set the decoder baud rate to 10000. Problems with 20 kHz are understandable though, because it's just a bit over twice the baud rate.
After this I rebooted into Linux because the Windows problems were getting too annoying. Installing sigrok was easy, because a Ubuntu package was available. I didn't have any problems in Linux. Here's some SPI. The Stellaris LaunchPad is communicating with an nRF24L01+ module and writing to some registers. This is at the maximum sample rate of 24 MHz.
As you can see, with a small piece of hardware you can order from China for $10 and some free software, you can have a 24 MHz logic analyzer which will decode protocols for you. That's truly impressive!

3 comments:

Boris Gjenero said...

I found the bug which is causing PulseView to crash at startup in Windows.

Carlos Diaz said...

Seems like pulseview still have problems in windows, i can´t save the .sr file, did you found this problem aswell?
Will give it a try on ubuntu, great post!

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