Misconceptions about USB Oscilloscopes like ADALM1000/2000
- You’ll have to carry around more stuff
This one is true assuming you don’t already carry around a laptop anyway. With a USB module like the ALM1000 or ALM2000 you need a computer, perhaps a lap-top or tablet, to run the software. These days, most students routinely carry around laptops. With laptops and tablets getting simultaneously less expensive and smaller, you can get a very portable, powerful computer to run your USB Oscilloscope for not a lot of money. That makes your computer, along with a device that is small enough to fit in your pocket, into a suite of personal lab instruments.
I don't think most people can image carrying around a set of bench instruments like an oscilloscope, power supplies etc.
This also may be true depending on the USB based instrument you choose. If it is truly only a USB scope, then yes, you will need other hardware or USB boards. However, with basically all of the signal manipulation done in software, many USB modules like the ALM1000 and ALM2000 also feature capabilities like curve tracers, impedance analyzers, network analyzers, spectrum analyzers, and even logic analyzers. This means you can fit a whole lab bench in your backpack.
- They need more space on your desk or bench than a standalone oscilloscope
This one is related to the first point, again possibly true. But unlike a standalone scope, the USB personal instrument module plus a laptop or tablet, can simulate and analyze your circuits, provide a place for you to view and record your data, browse the web for datasheets or research papers. The point being, your laptop is something you likely already use to work on your circuit design project, and provides many more functions other than just operating the USB module.
- The User Interface is not the same as the bench and will be difficult to use
The User Interface on most USB based instruments is separate software that you download and install on your computer. If you are relying on this to be exactly like a traditional bench scope, then it may be a bit of a surprise. However, most of the software, such as ALICE for the ALM1000 or Scopy for the ALM2000, is designed to combine the functionality of a traditional bench oscilloscope or other instruments, with the user interface features that are common among desktop applications. So if you are familiar with your computer's OS and have some understanding of the kinds of functions found in the bench instruments, the interface should be relatively easy to navigate.
Something that is unique to the software that drives USB instruments, is that if you do get stuck or can’t find something, the documentation is often built in to the software, or easily accessible on the same computer. For example, ALICE includes balloon help, tool tips that pop up if you hover the mouse cursor over many of the buttons for a few seconds. Also there is a fast link to the user guide page on the ADI Wiki. If you can’t find it there, there are also helpful examples on the Wiki or EZ Virtual Classroom.
Something else that is unique to USB instruments vs the bench, is that most of the functionality is, as we've said, implemented in the software. This means that the developers are continually improving the usability and features of the device. This is a huge value add, and at no additional cost to the users. Be sure to check regularly for updates to the software. Feedback received from users posting on EZ is a good source of ideas for improvements or new features.
- They only provide fixed step ranges
This may seem true at first, but is not. The spin box or entry widget where you select values, sequences through fixed step values, but you can also type in any value you would like ( and maybe have to hit the return key to have it take effect ). You can also use the scroll wheel on your mouse or the up-down arrow keys to fine tune the values like you would a knob on a traditional scope.
- They have a very limited signal range, some only 5V!
This depends on the specific USB module, but is not a general rule. The ALM1000 has a built-in range of only 0 to +5V but with the simple addition of two or three resistors to make a voltage divider and a capacitor for frequency compensation, just about any voltage range is possible.
The ALM2000 in particular has an input range of between positive and negative 25V. It is also possible, through the use of a BNC connector adapter, to use standard 1X/10X scope probes with these modules.
There are other USB oscilloscopes that have much higher input range than plus or minus 5V, and USB oscilloscopes with smaller input ranges as well.
- They only have one or two input channels.
The ALM1000 and ALM2000 provide two built in analog input channels. However, in the case of the ALM1000 and the ALICE software, the user can expand the B input channel to up to 4 additional channels through the use of simple, readily available, low cost 4 into 1 analog multiplexers such as the ADG609 or the CD4052. Off the shelf analog MUX boards from SparkFun make this relatively easy to do. Including the A channel this provides a total of 5 analog scope channels.
- The cost of the USB module plus lap-top is more than a bench scope.
If you don’t already have a computer or tablet, you will need one to operate a USB instrument. Assuming you already have one, then the investment will only be the cost of the USB module, which ranges between $37.50 for the ALM1000 and $99 for the ALM2000. There are other USB scopes on the market that cost less and cost a lot more.
Now let's assume that you don’t have a laptop or tablet you wish to use with the USB instrument. Say you buy an ALM1000 for $37.50, and/or ALM2000 for $99 which provide many more functions than a bench oscilloscope ( but at perhaps less bandwidth ). Then you’ll need a laptop. At the local Walmart store you can get a quad core 2-in-1 10" touch screen tablet running Windows 10 and 32 gig solid state drive for between $100 and $200, this is more than sufficient for running ALICE or Scopy, but maybe you’d like to run other programs at the same time. Even so, the cost, maybe $350 for ALM1000 + ALM2000 + computer, is still less than a standalone scope with the same features let alone needing to buy power supplies, DMM and other bench instruments. You could add the ADALP2000 analog parts kit at $45 and still be less than a low end bench scope.
- They communicate over USB so response time is slow and sluggish
In general, the data acquisition of a USB instrument happens on the device itself. Then once the sample buffer is full, a set of data is sent over USB 2.0 to the software. As for the ALM2000, the device performs acquisition up to 100MSPS of up to 8000 samples for the two data channels. It can take a few milliseconds to send this data to PC and to start a new acquisition. So, while limited by USB 2.0, definitely not slow and sluggish. The ALM1000 continuously streams samples for all four data channels ( 2 for volts and 2 for current ) at 100KSPS.
I have used standalone scopes for all of my career and over the last few years USB instruments like the ALM1000 / ALM2000. Clearly, each one has its strengths and weaknesses, but don’t let misconceptions allow you to make the wrong choice.
As always I welcome comments and suggestions from the user community out there.