Digilent Analog Discovery 2 - Page 1
Forum section: electronics / testgear

author: Electro Fan
author_rank: Super Contributor
timestamp: January 09, 2016, 01:33:15 am
content: Attached are a couple images. The first shows an Analog Discovery 2 probing an Arduino-based 8 bit counter. In this photo you can see that the AD2 is using the BNC probe accessory board and that the board is also acting as a pass through so that the digital leads can be used at the same time as the scope probes. The scope probes are 1x/10x probes from Digilent In the second (very poor) image you can see waveforms from two analog channels and 8 digital channels displayed on the Digilent software. The software runs on Windows and Mac along with other operating systems. The software takes just a bit of learning but it offers a lot of mixed use possibilities. You can see (barely) in the photo that the 8 digital channels have been combined into a bus with an interpreter that has summed the parallel channels into 8 bit Byte values. The LA function also supports UART, I2C, and SPI. The various cursors and measurements work on both the scope and LA functions. It's possible to open additional windows beyond the analog scope window and the digital logic analyzer window to show a FFT window and more. It's kind of neat having the scope channels, LA, and the FFT all going at the same time. Another function included is a signal generator. While the images I quickly took are lousy the actual renderings on a computer screen are very good. All in all, if someone needed to keep the budget and bench space down but wanted a bunch of test tools, especially for learning, the Analog Discovery 2 has a lot going for it.

author: matseng
author_rank: Frequent Contributor
timestamp: January 09, 2016, 03:53:15 am
content: Insider tip: Don't take a photo of your computer screen - you have a button named PrtSc on your PC keyboard that will make wonderfully sharp and nice screenshots without bluriness, barrel distortion or vignetting. :-)

author: Electro Fan
author_rank: Super Contributor
timestamp: January 09, 2016, 04:02:12 am
content: Quote from: matseng on January 09, 2016, 03:53:15 amWow, really?

author: matseng
author_rank: Frequent Contributor
timestamp: January 09, 2016, 04:08:16 am
content: Quote from: Electro Fan on January 09, 2016, 04:02:12 amNo... Just kidding The correct key is cmd-shift-4 ^_^But the Discovery truly is a nice device that can easily be thrown into a bag when travelling. I've had the previous version for some years now and had good usage for it. The day it gives up the ghost I'll probably get the AD2 (or the AD3 if it takes too long for it to break)...

author: miguelvp
author_rank: Super Contributor
timestamp: January 09, 2016, 04:13:39 am
content: I use Alt-PrtSc so it only captures the window that has currently focus.Electro Fan, congrats on the device, I have a 1st Gen and comes in handy.

author: Electro Fan
author_rank: Super Contributor
timestamp: January 10, 2016, 11:30:53 pm
content: Simple silly question, but is there a trick to getting the Analog Discovery to read a simple DC signal? Just trying to observe a flat line at an appropriate amplitude when probing a AA or 9V battery. Thx

author: pascal_sweden
author_rank: Super Contributor
timestamp: January 11, 2016, 04:12:53 pm
content: I think that the new design looks a bit overdone. Well, as always that's a personal taste of course.The older design looked more down to earth IMHO.Haven't bough such a unit yet, but maybe I should source the old model soon, before the new science-fiction design takes over

author: eas
author_rank: Frequent Contributor
timestamp: January 11, 2016, 08:02:58 pm
content: Quote from: Electro Fan on January 10, 2016, 11:30:53 pmDC vs AC coupling?

author: Electro Fan
author_rank: Super Contributor
timestamp: January 12, 2016, 05:39:02 am
content: Quote from: eas on January 11, 2016, 08:02:58 pmYep, DC coupling - I thought that might be it but I looked through all the software menus and couldn't find it, so based on your encouragement I decided to read the manual; it turns out that DC and AC coupling are changed with a jumper on the BNC accessory board. A bunch of software menus and controls but coupling is set with hardware. Works fine on DC

author: mtdoc
author_rank: Super Contributor
timestamp: January 12, 2016, 07:00:48 am
content: Quote from: Electro Fan on January 12, 2016, 05:39:02 amThis reminds me of an important point. When using the BNC adapter board, the two scope channels ARE NOT DIFFERENTIAL! Their grounds are tied together like on a traditional scope. This is not the case without the BNC adapter. So when using the BNC adapter board and 2 channels, make sure both ground leads are at the same potential!

author: Electro Fan
author_rank: Super Contributor
timestamp: January 12, 2016, 07:40:53 am
content: Quote from: mtdoc on January 12, 2016, 07:00:48 ammtdoc,Thanks for the caution.The current layout is a PC (MacBook) with two USB ports.One USB port is powering and programming an Arduino Uno. The Uno is in turn powering a breadboard with an 8 bit Byte LED counter. (The Uno is presumably being powered at 5V by the Mac USB; the Uno is powering the breadboard at 3.3V.)The second USB port on the Mac is powering the Analog Discovery board and communicating the Analog Discovery Waveforms app. The BNC board plugged into the AD supports two conventional probes, each with a ground clip. One probe is probing one of the data channels (LEDs) on the breadboard. The other probe is probing a second data channel (LED) on the breadboard. The BNC board is also acting as a pass through for the digital leads on the Analog Discovery - 2 of those leads are also probing the first 2 data channels (LEDs) - same channels as the conventional probes - on the breadboard, and the next 6 leads are probing the remaining 6 data channels (LEDs) on the breadboard.So, the Mac is powering the Uno/breadboard and the AD while the AD is probing the Uno/breadboard. The two conventional probes from the AD are both grounded to the same pin on the Uno/breadboard. So they should be at the same potential, yes?PS, sometimes the Mac runs low on battery power - so sometimes it is plugged into AC while it's powering the AD and the Uno/breadboard (and of course while running the Uno IDE and the AD Waveforms app).

author: mtdoc
author_rank: Super Contributor
timestamp: January 12, 2016, 08:13:36 pm
content: Quote from: Electro Fan on January 12, 2016, 07:40:53 amYes - that's the key bit. They don't necessarily both need to be on the same pin - but both ground leads need to both be attached to points with the same potential - otherwise you are creating a short between the 2 points and depending on the current available - could fry your ground leads (and maybe the DUT).If not using the BNC adabpter board it doesn't matter - the "1-" and "2-" can be at different potentials and so each channel is truly differential.

author: Electro Fan
author_rank: Super Contributor
timestamp: January 13, 2016, 04:27:38 am
content: Quote from: mtdoc on January 12, 2016, 08:13:36 pmSo just to clarify/confirm, probing multiple points without the BNC adapter board - with just the digital leads - with different potential is fine, yes?When using the BNC adapter board is there anyone additional safety or room for error if the PC powering the AD is running on battery power vs. AC? Either way (via PC battery or PC AC power) with the BNC adapter board is the potential problem for the DUT or the PC or both?

author: mtdoc
author_rank: Super Contributor
timestamp: January 13, 2016, 08:15:30 am
content: Quote from: Electro Fan on January 13, 2016, 04:27:38 amYes - on my AD (the original), the 2 scope input channels are labeled 1+/1- and 2+/2-. Without the BNC adapter board 1- and 2- are independent and can be a different potentials relative to each other - no problem. With the BNC adapter hooked up, 1- and 2- become tied together via the BNC shielding/probe ground clips (just like they are on a traditional scope).QuoteWell, when using a laptop on battery power you're isolated (like a handheld scopemeter)if that's what you're asking. I'm not sure but depending on the laptop when plugged in (2 pin AC adapter) you may also be isolated - but someone will surely correct me if I'm wrong. That is a different issue than the 1- and 2- being tied together with the BNC board though .Of course regardless, standard probing precautions, etc (see Daves video on the subject) apply.

author: GBowes
author_rank: Contributor
timestamp: January 14, 2016, 01:57:19 am
content: I came very close to buying the AD2 a few days ago after some extensive research and comparison. In the end I did not buy it for two reasons:One, it has very limited sample size/storage;The second was that I got tired of having to filter the technical details that were buried in the PR department's fluff.I do think it is a great device for the stated purpose, training/education; but am not quite so sure that it is not a little weak as a shop tool for serious analysis and troubleshooting.I think that if they intended that use, they would have increased the memory depth in this revised model.I read a comment somewhere on EEV Blog that National Instruments would not want this to compete with their "real" shop equipment. There may be more than a little truth in that comment.Just a comment re: the differential inputs. They are differential with a but. Depending on power source (USB or wall wart) and other external connections on the pc, one must be careful with your ground connections.Here is a direct quote from the reference manual that is worth reading. I almost get the idea that they do not want you to read it as it can take several readings.A clear schematic showing these grounds would have been a lot more useful!!!"Important Note: Unlike traditional inexpensive scopes, the Analog Discovery 2 inputs are fully differential. However, a GND connection to the circuit under test is needed to provide a stable common mode voltage. The Analog Discovery 2 GND reference is connected to the USB GND. Depending on the PC powering scheme, and other PC connections (Ethernet, audio, etc. – which might also be grounded) the Analog Discovery 2 GND reference might be connected to the whole GND system and ultimately to the power network protection (earth ground). The circuit under test might also be connected to earth or possibly floating. For safety reasons, it is the user’s responsibility to understand the powering and grounding scheme and make sure that there is a common GND reference between the Analog Discovery 2 and the circuit under test, and that the common mode and differential voltages do not exceed the limits shown in equation 11. Furthermore, for distortion-free measurements, the common mode and differential voltages need to fit into the linear range shown in Figs. 12 and 13. For those applications which scope GND cannot be the USB ground, a USB isolation solution, such as what is described in ADI’s CN-0160 can be used; however, this will limit things to USB full speed (12 Mbps), and will impact the update rate (screen refresh rates, not sample rates) of the Analog Discovery 2."Graham

author: Electro Fan
author_rank: Super Contributor
timestamp: January 14, 2016, 03:33:22 am
content: Quote from: GBowes on January 14, 2016, 01:57:19 amSo in case I don't have my engineering lawyer with me, is it your opinion that it's safe to use the AD2 with the BNC probe adapter board and two probes to probe a DUT (such as an Arduino Uno) if both the AD2 and the DUT are powered by USB ports on a PC?

author: Fungus
author_rank: Super Contributor
timestamp: January 14, 2016, 06:54:43 am
content: Quote from: GBowes on January 14, 2016, 01:57:19 amYep. As s tool for learning/messing about with electronics it's pretty damn good.Quote from: GBowes on January 14, 2016, 01:57:19 amThat' not its target market.

author: GBowes
author_rank: Contributor
timestamp: January 14, 2016, 11:35:57 am
content: @Electro Fan,Yes, IMO you should have no problem. Your only ground references are all at the same potential so no worries.This issue probably only should really be a concern when working on devices that are also somehow connected to the AC mains, or have different circuits at different voltages that are isolated on the DUT.GrahamQuote from: Electro Fan on January 14, 2016, 03:33:22 am

author: Howardlong
author_rank: Super Contributor
timestamp: March 13, 2016, 08:04:12 pm
content: I did a quick side by side comparison vid today between the Analog Discovery 1 and 2, particularly concentrating in the bandwidth of the scope.https://youtu.be/HXu2RxfJkKc

author: mtdoc
author_rank: Super Contributor
timestamp: March 13, 2016, 08:16:53 pm
content: Quote from: Howardlong on March 13, 2016, 08:04:12 pmExcellent Howard! I've been waiting for someone to do this. So essentially the same bandwidth of about 34 MHz on both!. This confirmed my suspicions.It's a great device in either version.

author: Howardlong
author_rank: Super Contributor
timestamp: March 13, 2016, 08:48:04 pm
content: In the video, I mentioned I use it while travelling. Here's how I get away with it on a plane, i put the setup inside an amenity kit, strategically place paperwork on top of it to obscure the cable, and hope no-ones watching if I need to change a probe point.The sparkies might like this one too, I made my own PAT Tested sticker from a post it note so she'll be right. Usually I find the onboard power points trip without much effort but I got lucky here.

author: mtdoc
author_rank: Super Contributor
timestamp: March 13, 2016, 08:53:19 pm
content: Living dangerously letting that be visible even briefly on a plane in this age of terrorist hysteria!

author: nctnico
author_rank: Super Contributor
timestamp: March 13, 2016, 09:41:12 pm
content: Quote from: mtdoc on March 13, 2016, 08:53:19 pmI agree. I'm amazed they even let it onto a plane!

author: Howardlong
author_rank: Super Contributor
timestamp: March 13, 2016, 09:59:21 pm
content: Quote from: nctnico on March 13, 2016, 09:41:12 pmThankfully paranoia is yet to be global, but I do frequently get chosen for secondary screening and swabbing, about half the time I'd say in the US and UK, and it's definitely in proportion to the amount of wiring and other paraphernalia you have coiled up in your bag. Some jurisdictions are rather less paranoid than others, of course.

author: mtdoc
author_rank: Super Contributor
timestamp: March 13, 2016, 10:11:34 pm
content: Quote from: Howardlong on March 13, 2016, 09:59:21 pmMy favorite personal anectdote of security screening paranoia occurred in 2002 when I was on my way to Kenya to do some medical work. I had in my carry on bag some medical equipment including a pair of hemostats and a needle driver (short blunt hemostat like). Passing through Dubai airport security pulled them out of my bag - understandably since they looked somewhat like scissors. But even after showing the very serious non english speaking security officer that they were not scissors and had very blunt ends he refused to give them back. I had to get his supervisor involved. I'm still not sure how he thought they could be used as a weapon - perhaps by clamping them onto someones ear?