DSO Nano scope or logic analyzer?

by sangamon on Fri Mar 15, 2013 5:34 pm

Is the new DSO Nano v3 scope (#468) suitable for Arduino projects? Or would I be better off with a logic analyzer like the Salae Logic - 8-Channel USB logic Analyzer (#378)?

I have some situations where I'm seeing odd results. For example, I have the GPS ultimate breakout (#746) providing time to display on a 7 segment I2C backpack (#878). Occasionally the display will stop updating, or one of the segments will blank. I'm suspecting that a signal is not correct or not up to spec (probably because of my wiring).

I'm new to a lot of this, so I want to get an appropriate tool to view the signals.

Thanks.
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Re: DSO Nano scope or logic analyzer?

by BruceF on Fri Mar 15, 2013 6:04 pm

That's a bit like saying, "I'm going to do some woodworking, should I buy a hammer or a saw?"

I don't know what to suggest for your toolkit. Ideally I'd say get a Rigol and a Salae, but budgets being what they are... Personally I have a DSO Nano and no logic analyser. I'm not particularly impressed with the Nano, to be honest. I find its UI painful and slow to work with. The portability is great, but for any serious analog debugging I hunt down a real scope.

In any event, it's not going to be very easy to guess which tool might give you visibility into your problem just from a forum post. Maybe you could start by outputting a bit of heartbeat data over the serial console and see if your AVR is still operating as expected? That might give you some clues to work with.
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Re: DSO Nano scope or logic analyzer?

by sangamon on Sat Mar 16, 2013 11:50 am

I guess the question that I should have asked is "is the DSO Nano v3 fast enough to monitor I2C on the Arduino?" My suspicion is that it is *not*, given the 100 kHz bandwidth. I wonder if anybody has used it with such Arduino projects. Thanks.
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Re: DSO Nano scope or logic analyzer?

by cstratton on Sat Mar 16, 2013 12:54 pm

sangamon wrote:I guess the question that I should have asked is "is the DSO Nano v3 fast enough to monitor I2C on the Arduino?" My suspicion is that it is *not*, given the 100 kHz bandwidth. I wonder if anybody has used it with such Arduino projects. Thanks.


That depends on how fast the I2C is, and to what degree you want to monitor it. It would be at best marginal for the original slowest I2C spec, more importantly, even if you could capture the nominal data, often the point of using a scope rather than a logic analyzer is to look at the analog quality of a signal, and for that you need to sample at many times the frequencies of interest.
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Re: DSO Nano scope or logic analyzer?

by adafruit_support_mike on Mon Mar 18, 2013 12:12 am

sangamon wrote:I guess the question that I should have asked is "is the DSO Nano v3 fast enough to monitor I2C on the Arduino?" My suspicion is that it is *not*, given the 100 kHz bandwidth. I wonder if anybody has used it with such Arduino projects. Thanks.

If you want to snoop I2C traffic (or other protocols) take a look at the Bus Pirate: http://www.adafruit.com/products/237

It's more specific than a 'scope or straight logic analyzer, but is the Swiss army knife of inter-chip comms testing.

BTW: you're correct that the Nano's low bandwidth rules it out as a tool for debugging I2C or SPI at real-world clock frequencies. It's handy for prototyping.. many circuit designers start by making a low-frequency version of a circuit so they can get the basic functionality working and play with parameters to get a feel for how the thing behaves. Then when the core features are working, they start building for speed. Tools like the Nano give you useful information about circuits in the "let's see if/how this works" range, but aren't up to the challenges of reading chip overhead when the frequencies get up into the fast I2C/SPI ranges.
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