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What is a Digilent Analog Discovery 2?
The Digilent Analog Discovery 2 is more than just an oscilloscope; it is a measurement tool that can record the signals on its inputs, can also be used as a signal generator and will control mixed signals. It interfaces with a PC through a USB port which also supplies its power. An oscilloscope is pretty essential to both hobbyists and professional electronic engineers alike, to monitor the changing nature of a signal in a circuit being debugged and correlate it to other signals in that circuit. The ability to record the digitised analogue data (a storage oscilloscope) is an advantage for signals which need to be analyzed post measurement. e.g. when the signal is not periodic.
Whilst waiting for it to arrive, I took a look at Digilent’s website (https://digilent.com). There are a number of accessories that are available including BNC Adapter, Breadboard Adapters, Transistor Tester, Audio Adapter and Impedance Analyzer Adapter.
Unpacking the instrument and its adapters
The instrument arrived in two packages on separate days containing the Analog Discovery 2, Audio Adapter (212-2084) (Figure 1) and Transistor Tester (222-2680) (Figure 2). You will also require the Discovery 2 and I'd recommend the development kit (193-2595)
The pictures below show what these look like as they are taken out of their packaging.
The Analog Discovery 2 comes packaged in a project box (Figure 3) which appears to provide a reasonable level of projection. However, it isn’t large enough to contain the adapter boards.
Unpacking, I noticed that the Analog Discovery 2 has a power supply socket. Searching the online documentation reveals a mention of its use to provide additional current for output ports. I was unable to find a specification for this power supply and contacted Digilent. I didn’t submit my support request through the ‘support forum’ (https://forum.digilentinc.com/), using the Sales and Order Support form (https://digilent.com/shop/sales-and-order-support/) instead; at this stage, I felt this was more of a documentation issue than a true technical problem. I have been recommended a suitable power supply but a week or two on, am still waiting for the actual requirements specification.
The basic Analog Discovery 2 kit contains the Analog Discovery 2, a USB cable to connect the instrument to a PC, a 2x15 signal cable assembly, a pack of five 6-pin male headers, a snap-on cable ferrite (presumably for the USB cable) and labels for each wire in the signal cable assembly (Figure 4). The instrument is a single PCB housed in a shaped plastic box, which affords it some protection. The two adapters arrive in antistatic bags and are essentially PCBs.
The USB port on the Analog Discovery 2 is mechanically constrained only to the PCB by solder, as is the signal cable assembly socket. This is of concern as repeated insertion and extraction could cause signal degradation or indeed fail. In order that the instrument can be returned to the project box for storage or transport the USB cable and signal cable assembly must be removed.
Installation and operation
I chose to download and install the Waveforms software to a 10+ years old laptop running Fedora 34 Linux (rpm package at (https://digilent.com/shop/software/digilent-waveforms/download)) as, in general, installation on a Linux platform can be more difficult. However, it was very easy; following the instructions at (https://digilent.com/reference/software/waveforms/waveforms-3/getting-started-guide). This required the installation of the Adept Runtime package prior to Waveforms.
I connected the Analog Discovery 2 to the USB port of the PC and double-clicked on the Waveforms icon in applications. Waveforms started and detected the instrument immediately. The window presented by waveforms, at first sight, looked quite busy, however, this was probably a combination of the necessity to control all the features of the instrument and it being displayed on a smallish laptop screen.
Clicking the run button in the oscilloscope tab and touching the oscilloscope wires in the signal cable assembly showed that the instrument was detecting electrical noise and displaying it. I hadn’t at this stage attached the wire labels so identified the scope wires from the reference manual (https://digilent.com/reference/test-and-measurement/analog-discovery-2/reference-manual). I would have found it useful to download a PDF of this manual, both because I tend to prefer to use a printed copy and I want to use the instrument in a situation where I don’t feel comfortable connecting to the available public Wi-Fi.
After establishing the signal cable assembly wires for the waveform generator, I used one of the 6-pin male headers to connect its output to the channel 1 input of the oscilloscope, connecting also their respective GND’s. The oscilloscope displayed waveforms commensurate with those setup in the waveform generator (Figure 5).
Selecting the Fast Fourier Transform (FFT) tab and clicking the run button allowed a frequency sweep setup on the waveform generator to be seen sweeping along the horizontal (frequency) axis (Figure 6).
I spent a little time using the Analog Discovery 2 with the Audio Adapter with my CodeDojo (https://coderdojo.com/) group which is part of the Raspberry Pi Foundation. Here, young students (ninjas as they are known) learn to code, often using BBC microbit’s, Raspberry Pi’s and other embedded devices such as Mona robots (https://ice9robotics.co.uk/category/mona). The demonstration involved playing some music from the earphone output of one of their mobile phones through the Audio Adapter and observing the output on the oscilloscope and FFT. This really engaged a wide age range, including parents. Some recognised this was similar to equipment (a traditional standalone oscilloscope) that they had seen in the science lab at school. I intend to pursue its use with them over the coming months, encouraging them to write code to control outputs of the BBC microbit with their code and observing the effect on the oscilloscope. Also, they will be encouraged to use the waveform generator as input to the BBC microbit.
I was keen to use Analog Discovery 2 to debug a fairly complex clock dividing circuit on a PCB, however, as yet I haven’t acquired the BNC Adapter. I think this adapter is a must-have (134-6460) , not only to allow traditional oscilloscope probes to be connected but to increase the oscilloscope’s bandwidth from 9 MHz to 30 MHz. The higher-end here appears to be quite respectable in comparison to other competitors’ devices at a similar price.
So far I have only used the Analog Discovery 2 for fairly ‘inert’ measurements. Users should have their attention drawn to the first paragraph in Section 2 of the reference manual (https://digilent.com/reference/test-and-measurement/analog-discovery-2/reference-manual) entitled “Important Note”. This discusses the grounding arrangement which seems to require knowledge of the grounding arrangements for the whole system, including the PC/laptop.
This leads me to a concern relating to the electrical isolation between the Analog Discovery 2 and the PC/laptop. I haven’t found anything describing this. Whilst I can’t say it has none, I would welcome being able to power it from its own power supply and electrically isolating it from the PC/laptop. e.g. using opto-isolation on the USB interface. This could help to prevent damage to the PC/laptop by an errant grounding or measurement.
The Analog Discovery 2 is a multifunction instrument, the feature range of which is provided at, what appears to be, a competitive price. I feel that it is useful as a tool for experimenting and prototyping, probably in an educational setting. i.e. not as a professional piece of equipment, noting that Digilent do sell a Pro range (222-2677) but significantly more expensive. I would welcome the introduction of an enclosure in which the Analog Discovery 2 can be securely mounted and cabled to more traditional oscilloscope/waveform generator front panel connectors. In addition, the confirmation or incorporation of electrical isolation from the PC/laptop would resolve a concern. I found the support could have been better. The Waveforms software is easy to deploy and intuitive, to the extent that I have used it. All in all, a good piece of equipment for the price.