Sample rates, combined digital and analog

Hi Saleae Team. Thanks for a great product.

I have used Logic 1 for a couple of years and built up an automated test setup where I use a Pro 8 device for nightly verification of a stepper motor control. I verify both speed, acceleration and motor current.

I use 1 analog and 4 digital channels, where the digital channels need very high sample rates (at least 50 MS/s) - but the analog channel needs a very low rate (down to 100 S/s) to allow sampling for long durations.
This is working alright but as I have discovered that Logic 2 has been updated with automation, I want to migrate to Logic 2. However, I see that Logic 2 is not (yet) supporting the sample rates I need.
How are your plans for additional combinations?

Another approach (which I only dare to dream about):
What if the analog sampling could be triggered by the edges of a digital channel. That would be perfect for me :smile:

@jcbruun53 We’re glad to hear you’re getting started with the newer Logic 2 Automation API!

I’ve added a comment for you in the feature request post below to track your need for this (I’ve written up some notes in the link below as to the challenges we face with implementing this feature, which makes it a non-trivial addition).

We unfortunately don’t have this on our roadmap at the moment. Out of curiosity, and to understand your use case properly, can you share your reasoning for needing a 100 S/s analog sampling rate, while also sampling at 50 MS/s digital? For example, I’d be curious to know what kind of signal frequency you are working with.

You could consider a workaround by using our Automation API to record several smaller captures instead of a single, longer capture. This would help save on RAM usage at the time of the capture (since each recording can be closed and cleared from RAM), but wouldn’t save on hard disk space if that was what you were going after.

If I understand your request correctly, triggering by the edge of a digital channel is in fact the only method to trigger recordings (we don’t have a method for triggering on analog channels at the moment). For example, in the scenario you mentioned (“I use 1 analog and 4 digital channels”), the edge trigger could be enabled on one of the 4 digital channels, which would trigger the entire capture to start.

I suspect I could be misunderstanding a part of your request, so feel free to correct me if I made an incorrect assumption about your setup! Hope this information all helps.

Thanks for your quick response. And for your curiosity:
I am verifying the sw-driver for a steppermotor, driving a rotating device. During each round the rotational speed (stepper pulse frequency) is varied from 1Hz to 33kHz.
I need to measure the acceleration/deceleration of stepper pulses with 0.1% accuracy, which leads to the requirement of at least 33MS/s, digital.
We also measure an analog voltage, which controls the current in the motor windings. To optimize the torque, this current is varied multiple times during one round.
To verify this, an analog channel is used, but here we can live with a lower accuracy.
Now, the duration of one round is varied from 0,3 seconds to 1 hour in different use cases. To measure a full round I need to sample for up to 1 or 2 hours.
This is actually possible if the analog sample rate is kept at 100S/s.
I really hope you will be able to lower the analog sample rate significantly - until then I will stick to Logic 1.

Regarding the last part: My mistake, sorry I Should have written:
What if each analog sample was triggered by an edge of a digital channel. Then we would only get as many analog samples as there are edges on the selected digital channel,
and sometimes that is all one needs. But I know that is a huge change to ask for :slight_smile:

100S/s for a couple of hours is only on the order of 1.5MByte. With a modern computer 100x that size shouldn’t be much of an issue. Is there something else going on that I’m missing?

Note that only edges are recorded for digital channels so bumping the digital sampling rate to 125MHz shouldn’t impact the size of the recorded data.

I agree. I don’t have to go as low as 100S/s, but the point is: With a digital rate of 125MHz Logic-2 will not allow me to go below 3.125 MHz analog… and doing that for 1 hour requires 11.25 GB of RAM - and I don’t have that.

My bad! I missed that this issue was in the context of automation where the rules and allowed rates are different. I’ll shut up now and go back to my corner.

@jcbruun53 Ah, I get it now, thanks for describing your use case in more detail. That all makes sense. I’ll ping the team about your request, but unfortunately, we’ll likely not be able to work on it soon due to other priorities at the moment. You’ll unfortunately need to stick with Logic 1.x is this is an absolute must.

The ability to trigger samples via an external input clock is something we’ve wanted to support for quite some time now, but just haven’t gotten to working on it.

Hehe, no worries. I’m grateful for your response :grinning:

Ok, I will stick with Logic 1.2.29 for now but as I expect my test to be running every night the next couple of years (testing on a developing product), I will look for your upgrades and hopefully be able to switch to Logic 2 at some point.