I am considering purchasing the Saleae Logic Pro 16 for a task that needs to be completed. Appreciate if anyone could help out answering some questions
To measure :
The Digital Signals operate at 62.5Mhz
The Analog Signals operate at 1 Hz and 1Khz
The following is the planned strategy:
10 bit digital data ( @250Msps) will be used ( 9 bits data & 1 bit for clock)
2 Analog channels will be used ( @50Msps) ( pulses )
NB : The analog channels should provide the triggering for data capture and end.
Questions :
is 250Msps enough to reasonably recover the 62.5Msps digital data ? ( i believe 4 th harmonic can be captured)
is there any buffering on the Logic pro Device ? , if so what’s the limit ?
I need to capture 2s of data, we have the option to use 32GB Memory PC , would that be enough ( if live streaming is used)
I would like to post process the data in python , i believe the SW allows to save data in CSV format, can you please confirm
Can we trigger on pulse data ( put in the Analog channel) ?
Quick answer – it should work fine, but should confirm some details.
Overall/digital:
How many total signals/channels do you need to capture? What is the digital I/O voltage levels of each (5V, 3.3V, 2.5V, 1.8V, 1.2V or ?) and are they all the same?
What is fastest time between digital edges?
What type of signal/encoding will be captured?
Analog needs:
1 Hz analog in a 2s capture would have very little signal content?
1 kHz analog won’t need 50MS/s capture, as the amount of analog capturing most impacts performance & storage demands.
As I recall, the answer to this is no. Only digital channels can be used.
As for the amount of memory required for the dinal sampling, the input is compressed (RLL encoded?) so if there’s not a lot of toggles, you can sample an impressive amount of data. I’ve streamed a couple of 250MHz analog data channels directly to the NVMe of my laptop for post-sample analysis.
As for the analog speed, there is an analog input anti-aliasing filter that scales with the sampling frequency that you might want to be aware of.
As far as capturing, @Kai is right that you can’t trigger on the analog data (only digital channels in the triggercapture mode), but the data is streamed real-time to your PC and uses host RAM instead of internal storage. Thus, you can just use a timed or looping capture mode and just capture a relatively large amount of data and trim/post process it afterwards.
The amount of RAM needed for a given capture depends on your channel settings, PC performance, and the captured data characteristics. The biggest resource hog is the analog data (you’re storing a multi-byte value for each & every sample), so best to use the lowest analog sampling rate you can tolerate (and turn off all unused channels) if logging for a long capture time. Also, if your PC is too slow, your USB ports/drivers are outdated, and/or your USB bus with the logic is shared with another device – you can also run into performance problems on the host side.
If you just need digital, you can (and I recommend) capturing at the highest possible digital sampling rate, as the Saleae only ‘stores’ the edges/transitions, not every sample point in the same state. Thus, if it is a ‘quiet’ channel, you could capture for days or weeks (or longer) and not fill the capture buffer
In my own use, I often just capture everything without worrying about triggers and just post process the capture afterward. You can set a pretty big buffer and easily run for minutes (or hours) and not fill the buffer. So much easier than tweaking a trigger and/or sample rates on a traditional scope and rerunning the test until the snapshot got what I was looking for. Now, I just hit ‘start’, run the test scenario, and hit ‘stop’ when I’m done. Then, I browse the capture for what I’m looking for and can trim (if necessary) the extra before/after the ‘interesting’ time interval. The GUI is amazingly responsive to panning/zooming/searching around even with gigabytes of underlying data in a capture. A mouse w/ scroll wheel is definitely better than turning dials/knobs on a scope
Bottom line: your scenario seems like one a Logic Pro could easily handle. Depending on characteristics of your ‘analog pulse’ you might be able to trigger a digital channel on it. All 8 (or 16) channels can store either/both analog and digital. So, if the ‘pulse’ can be seen with the digital voltage levels, you can trigger on it digitally and still see the analog view of the same channel.
