Electronics > Beginners
Which logic analyzer?
robdejonge:
I'm increasingly getting myself into home automation, and playing with microcontrollers. I do not design my own circuits or anything, simply don't have the knowledge to do that just yet. But I have noticed a desire to be able to 'listen in' on communication between a microcontroller and a sensor, or something similar. So I've decided to get a logic analyzer. I can't afford a fancy scope, but can spend up to maybe $150 on a USB logic analyzer. The way I look at this is this will allow me to 'debug' communication between components, similar to how I use debug statements in software development.
So now .... I am facing the challenge of selecting one. Two main things seem to be important. First, the bandwidth and second the sample rate. I found this write up trying to explain it, but I failed to comprehend. So let me ask it in a typical newbie style ...
The fastest microcontroller I use is the ESP32.
What sample rate is required to adequately handle the fastest signal that comes out of that?
Gyro:
Welcome.
You may have your financial priorities the wrong way round. I would be tempted to purchase one of those <$10 8 bit Saleae clone logic analysers from ebay and use it with open source Sigrok Pulseview. If it doesn't meet your speed needs, then nothing much lost. It should be fast enough for general comms with sensors, protocol decoding etc.
Reserve the remainder of your money for a scope of some description, maybe a used analogue, maybe a USB one. Many problems with communication are caused by signal integrity issues, noise, dodgy logic levels etc. which a logic analyser will never see. At the same time, it gives you have a useful instrument for general debugging.
0xdeadbeef:
The topic has been discussed quite a few times here. I think the last time it was here:
https://www.eevblog.com/forum/testgear/cheap-usb-logic-analyzer/msg1875170/#msg1875170
In a nutshell: typically, the fastest protocol you will look at in the typical hobby scenario is SPI which goes up in the few MHz range (yeah, some people crank it up to 20Mhz or so but it's not really mean to).
Since you want to use a multiple of the fastest clock as sample rate, a logic analyzer should be able to sample with 100MSa/s or more.
However then there's the question whether the LA will store the sampled data in RAM (which limits amount of data it can capture) or if it transfers the data through USB (where the USB bandwidth limits the amount of data that can be transferred). Like just because an LA samples with 200MSa/s, this doesn't mean you can rely on a 15MHz clock signal to be sampled correctly if the transfer happens via USB2.
IMHO the best choice is to combine local RAM and USB transfer. So my typical recommendation at this point would be to look out for a DSLogic Plus. Note that only the Plus version has the local RAM and only the newest HW revision has a certified driver for Win10. eBay sellers will typically try to sell the Basic version without SRAM or an older version of the Plus which doesn't have a certified Win10 driver.
Personally, I still use my Ikalogic ScanaPlus most of the time (though I also own two DSLogic Plus which I use where the ScanaPlus fails) and will surely have a look at the new SP209 as soon as it's out. Unfortunately, the ScanaPlus is no longer available for quite some time and the SP209 will be more in the 300€ range.
robdejonge:
Thanks for the pointer, Gyro. A good friend keeps telling me to get a scope too, yet stubbornly I refuse to listen and focus on the realm I understand: digital. I have secretly been looking at second-hand ads too, but have so far not found anything of interest (Dutchman, living in Bangkok). I appreciate the suggestion that issues often stem from poor signal rather than signal content. I understand that.
What a super helpful response, 0xdeadbeef. Thank you for that. And my apologies for not first searching the forum. Thank you for taking the time to write that all up. I had been looking at the DSLogic Plus and was wondering if the Hantek 6022BL with its lower sample rate would suffice. But I'll be ordering the DSLogic Plus. Thanks again!
tggzzz:
--- Quote from: robdejonge on October 27, 2018, 10:38:12 am ---Thanks for the pointer, Gyro. A good friend keeps telling me to get a scope too, yet stubbornly I refuse to listen and focus on the realm I understand: digital.
--- End quote ---
The only digital circuits are fentoamp circuits and photon counting circuits; everything else is analogue.
What you think of as digital circuits are actually analogue circuits where the voltage/current is interpreted to be digital.
So, get a scope so that you can verify your analogue signals will be correctly interpreted as digital signals ( a.k.a. signal integrity). Then flip to the digital domain and use digital tools such as logic and protocol analysers.
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