analog discovery 2 Getting Analog Discovery 2...Q's about accessories...

[MetroWestMA]

Hi Everyone,

I was going to order an analog discovery 2 pro bundle but I qualify for the educational discount and wanted to figure out what accessories I really need.

1) Definitely wanted the BNC adapter board for $19.99

2) I can use any BNC probes with this, right?  Like I could order them from Amazon, etc. or use existing ones that I have?

3) I need to measure current on a 5V circuit around 1-5 AMPS for a battery powered project.  I bought two higher current .10 ohm resistors figuring I could connect probes against that to measure current and they would only slightly drop the voltage at these amperage ranges, but with a high resolution scope, I could go lower resistance.  Or can I get probes that do this for me?

4) Do I need the Mini Grabber test clips -- what are they for?

5) What is meant by "The Analog DIscovery BNC adapter board does not have differential  analog scope inputs?

6) Any other must have accessories?

Thanks in advance for any help or input -- this looks like a great little device (and sniffing various protocols and simulating GPIO will be great)!

MetroWestMA

[JColvin]

Hi @MetroWestMA,

1) Horray!

Let's see if I can answer your other questions.

2 & 5) The BNC Adapter board is only single ended. In terms of this board, this means that the negative differential input on the BNC adapter is hardwired to GND, so you will not be able to measure a differential signal without damaging your probes, even if you probes are designed for differential measurements. The Analog Discovery 2 does support differential inputs on it's oscilloscope designated pins, but the BNC Adapter board does not. So in principle you can essentially use any BNC probes you want with the adapter board, but you are limited in the application.

3) I'm personally not certain if there are any probes that will do that for you; I guess in principle a differential probe would let you measure the voltage across you resistor, but the BNC adapter board doesn't support differential measurements so you would need to use a different probe on each side of the load. I imagine you already know this, but the AD2 isn't able to measure current directly; you will need to have WaveForms calculate it for you. An example of how you might do this is available here.

4) The mini test grabber clips are a type of alligator clip. Their purpose is to attach to a small circuit or wire that you need to need make contact with but don't have a readily available test point header to use.

6) I'm of the opinion that you can never have too many of the pin header/gender changers but unless you are looking to have some other analog components to have around your work space, I don't think there's anything else that is a must-have, aside from the WaveForms software needed to run the AD2 of course.

Let me know if you have any other questions.

Thanks,
JColvin

[MetroWestMA]

JColvin -- thanks for your detailed response...just two other questions...

1) I can measure differentially using both channels and adding them with the BNC adaptor (saw several other generic scope posts on that), or by simply connecting test wires directly to the AD2 oscilloscope designated pins to my power source.  Nothing is high frequency here -- I am looking for drops in voltage when a cell modem is transmitting and some other power hungry devices are using transient current.

2) On the current issue, how much of a voltage drop can the AD2 measure reliably -- like could I put a very small resistor that would cause from a .01-.1 voltage drop across it at .5-5 AMPS and accurately measure voltage?

Thanks so much!

[JColvin]

Hi @MetroWestMA,

The Oscilloscope tool in the WaveForms software can set the range on the two ocsilloscope channels down to 100 uV/div, so you can measure some fairly small voltage drops. I believe you can safely and accurately measure a small voltage drop directly on the AD2 pins when there is up to 5 A of current on the 5V source, though I will defer to @attila on this if they feel differently.

By directly connecting the test points on your system to the AD2 and not using a BNC probe, you will lose out on being able to use any attenuation settings available on your probe for an easier measurement. Otherwise, if you did you two probes and the BNC adapter, you could add a math channel to compare the data directly in WaveForms. Some more information about the features available with the Oscilloscope are available here.

Let me know if you have any other questions.

Thanks,
JColvin

[attila]

Hi @MetroWestMA

The AD scope inputs have two physical gains/ranges. At 5V pk2pk range with 0.3mV resolution supports voltages up to +/-5V relative to its ground. The +5V is at the limit and to prevent clipping you might have to use 50V pk2pk range with 3mV resolution supporting up to +/-50V. The current measurement resolution will be scope resolution / shunt resistor. For current measurement usually a low shunt resistor value is used, like for 10A 10mOhms, and this low voltage drop <100 of mV pre-amplified for measurement.

When connecting the scope as differential make sure to also have a ground connection.
Be careful because the devices ground is connected to the computer through the USB cable.