I’ve just hooked up my Sparkfun “USB Logic Analyzer - 24MHz/8-Channel” which I bought in May 2020. It seems to introduce lots of noise via the GND connection. Photo-1 has my scope input connected to the GND pin on the analyzer. Photo-2 is the same, except that I’ve started PulseView.
Any idea what is happening?
Rick Watson
The ground pin on the logic analyzer is connected to USB ground and that’s usually connected to chassis ground somewhere in your computer. What you’re measuring is a ground loop from chassis ground, into your electrical system, through the ground prong on your scopes power cord.
You need to connect your scope probe ground to the ground pin on the logic analyzer to bridge out all that other noise you’re seeing, it’s all coming from other sources not the logic analyzer itself.
Are both of the GND pins on the logic analyzer supposed to be connected together (inside of the analyzer)? They don’t appear to be. Is a schematic of the board available?
–Rick
They should be, unfortunately we don’t actually make these so we don’t have a schematic for them.
WARNING – GND next to pin 6 is NOT GND!
I just went through two days of troubleshooting this device to figure out why my rotary encoders stopped working properly when I plug my GND into the GND next to pin 6… It’s because that pin is NOT GND on this device!!!
Sparkfun – you need to put out an advisory, update your instructions, and stop printing your label like this. I bought your specific branded version because I had put a higher level of trust and faith into your products because you seem to be operating at a higher level of responsibility. But, to see you say that you don’t own the board and don’t have schematics is a pretty bad response to provide your customers when I spent 2 minutes to visually trace that pin back to the CLKOUT/PE1 of the CY7C68013A-56 chip. It literally lands on the third pin clockwise from the “dot” (pin 54) on the chip – https://pdf1.alldatasheet.com/datasheet … 3A_08.html page 19 shows that is NOT GND. It’s next to GND, but “close” doesn’t work in this world.
As my first experience of buying a product that you guys sell as your “own brand”, finding no real instructions for it other than your “tutorial” post saying “Also connect on (sic) of the GND wires to GND.” It blows my mind – and you’ve even had customers telling you that something was off with the device.
Hopefully you receive this information well and you update what you need to update to inform your customers (past and future) about the true nature of the “GND” pin next to Channel 6.
Thanks goes to “Junior Patrick” on the Espressif MCUs Discord for pointing out that a different “brand” of this same board labeled the other pin CLK. It got me to actually do this tracing to discover the truth behind why the device was making my project misbehave.
Did it never occur to anyone at Sparkfun to ACTUALLY TEST whether the two pins labeled GND are connected? It is not all that difficult! https://ae01.alicdn.com/kf/HTB1rWvbi5CY … pg_q50.jpgTS-Chris:
They should be, unfortunately we don’t actually make these so we don’t have a schematic for them.
On the (early) unit I have, all the ground pins are connected to ground. SparkFun doesn’t manufacture this item despite our label being on it, it appears the manufacturer may have changed something along the way. I’ll ask our engineers to take a look, it could be a new design or the manufacturer might have sent the wrong version.
Either way, you should put a decent, clear notice on your product page warning people to be aware of it. This could cause damage to unsuspecting people.
OK, I just scoped one of these and I’m seeing a similar thing although I’m getting a 12 or 48MHz signal that’s about 4.3 volts. If I measure current between the two “ground” pins I see a about 16mA of current, enough to light a LED.
To make things stranger, either “ground” seems to work when looking at logic but that might be due to the large difference in frequencies between what I’m measuring and what the device is reporting.
I’ll add a note to the product page to not use the ground pin next to input 6 just to be safe and we will see if we can get the labels changed as well.
