Question

Hello,

Really enjoy the Analog Discovery 2!

Just beginning to play with the Logic Analyser, past day or two.

Just for fun, I connected five data pins to five different 555 ic chip pins,

using the "signal" choice, under bus type in the Logic Analyser.

 

Very interesting to see power go up and down all at the same time.

Helps in understanding what an ic chip is doing on many pins, in real time,

even if the representation is binary (on or off).

HOWEVER, I believe this tool was not designed for this use,

So I wanted to ask:

 

Q1: Should I avoid using the logic analyser, with ic chips?

 

Q2: IF I can do this safely, how might I change some of the traces

I see on the screen, such that they show "Analog Sinewave" instead?

 

The instructions do mention this, saying:

"With higher row height for Bus or protocol, the analog representation of the values is drawn."

Showing an image of a Sine Wave, instead of a square wave.

 

Even though I change the height of the trace tracks to 10 higher, the views remain square waves.

Any idea how I might get it to show sine waves (as per instructions) instead?

Or is this not possible with a "signal" choice for trace?

Thanks,

Roland Prevost

 

 

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Hi @rprevost453@gmail.com,

I have moved your question to a more appropriate section of the Forum.

I do not believe it is possible to view analog waveforms (such as a sine wave) in the Logic Analyzer tool. In general though, as long as the signals on the IC are following LVCMOS standards (as per section 9.3 on the AD2 reference manual), which I imagine most 555 timers do. If your timers are providing a sine wave, I would use the Oscilloscope channels of the AD2 to view those sine waves directly; the logic analyzer pins aren't equipped (from my understanding) to readily view analog signals.

Out of curiosity, which tutorial/instruction set are you looking at? I'm not finding the quoted phrase in the Using the Logic Analyzer tutorial, the AD2 reference manual, or the WaveForms 2015 reference manual.

Thanks,
JColvin

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Hi John,

Thanks for your quick reply, and moving my post to an appropriate section.

I will check to make sure the 555 is compliant with the relevant standards.

 

The phrase I sent you, as well as an image of the Sine Wave I mentioned, come from the HELP/instruction

file that comes with the latest version of WaveForms 2015, in the Logic Analyser section. Which is what

prompted my second question, in the first place. Since the "help manual" mentions it, I therefore

thought it might be possible.

 

Let me check again which section, just to make sure ...

Yup, it's right there at the end of section 3 - Signal Grid, under Logic Analyser, just before section 3.1

begins. There's an image of what's called a "Sine Wave Representation" there in the trace track

I believe.

 

Thanks again,

Rol

 

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Hi @rprevost453@gmail.com,

Hmm, I didn't know WaveForms could do that; I learned something new today!

Looking through the file, my understanding is that analog signal is just the aggregate of the signals detected on the Bus. Personally, I wasn't able to get the Logic Analyzer to show a nice sine wave like the one shown in the help file. I will defer to the creator of the WaveForms software (@attila) for more details on that particular demo.

Thanks,
JColvin

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Thanks for taking a look at this, and possibly passing it on to the creator of the software.

If it is an aggregate of the signals on the bus, that would not be particularly useful with

multiple inputs from a 555 chip, as I am (just for fun) doing.

Pleased if you learned something new, as that might assist others as well.

Best,

Rol

 

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Hi @rprevost453@gmail.com

Q1: The digital IO pins of Analog Discovery output 0/3.3V logic, as input the lines have PTCs and protection diodes to GND and 3.3V.
https://reference.digilentinc.com/reference/instrumentation/analog-discovery-2/reference-manual#digital_io
To use the digital lines as input (logic analyzer) you could add series resistor of about 1-10k to reduce the current drained from 5V logic signals to 3.3V through the protection diode.

Q2: The analog representation only shows up for bus and other protocols.
A signal only has two states, so the analog representation would be identical to the digital one.

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Thanks Attila, very helpful.

Found it instructive to see many of the 555's pins activities at once,

instead of limited to the 2 channels of the scope. Binary output,

of course, but still ok.

Thanks for the tip re:adding resistance to bring down voltage

to spec. Makes complete sense.

Merci,

Rol

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