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A Virtual ElectronicsWorkbench By Tim Blythman It’s great to work in a well-provisioned electronics lab with lots of bench space and plenty of test instruments and tools. But we don’t all have that luxury! So we decided to come up with a way to cram all the most essential electronics tools into a small space, such as a typical desk, sharing space with a computer and possibly other gear. We even managed to keep the cost low! W e noted in our Mini Digital PSU project starting on page 38 that its design was partly driven by the need to create a compact solution that would fit on a small workbench. Not only is the hardware for that design small, but because it can be controlled from a PC via a USB interface, it can be tucked out of sight altogether, taking up practically zero space on your bench. We realised that, in addition to a power supply, another vital piece of test gear which usually takes up a lot of bench space is an oscilloscope. USB oscilloscopes have been around for a while now, so we decided to look into adding one to our setup. BitScope Micro A ’scope is very handy to have when it is needed, but you might go weeks 80 Silicon Chip or even months without touching it. And we wanted to keep the cost low. After doing a bit of research, the BitScope Micro appeared to be a good option. It has two analog channels with 20MHz bandwidth as well as six digital logic channels – enough for common jobs like sniffing serial, I2C and/ or SPI traffic. It interfaces with programs that can run on Windows, macOS and Linux, including on the Raspberry Pi. There isn’t just one suitable piece of software, but several. A DSO program allows the BitScope Micro to be used as either a digital or mixed-signal oscilloscope, and it can also generate analog waveforms. There is also a Logic program which can perform protocol analysis, including SPI, I2C, CAN and UART and a generator program can be used to generate arbitrary waveforms. Australia’s electronics magazine The Micro is only one of an extensive range of BitScope test gear; their products all work with the same software. In any case, because the BitScope Micro is one of the cheapest USB oscilloscopes, and it can run from a Raspberry Pi, we decided to get one to test. And then we had an idea . . . The Virtual Workbench While testing the Mini Digital PSU, it occurred to us that sometimes it would be necessary to isolate the power supply output from the control PC. The grounds may need to be at different potentials; a direct connection cannot work as the ground of the Mini Digital PSU is is plugged into the ground of the USB host it is connected to, which is typically Earthed. You could use a laptop or notebook computer running from its internal siliconchip.com.au battery, but this exposes a second problem. Often, you are connecting to gear that might be faulty, or that could generate voltages that would damage your laptop. And you also need to touch that computer, so you want to be sure it isn’t being fed any hazardous voltages! Our Virtual Workbench takes care of both of these problems. How it works You’ve probably gathered by now that we’re going to connect the Mini Digital PSU and BitScope Micro to a Raspberry Pi. The Pi is undoubtedly less expensive than a laptop, but that doesn’t give us any isolation. To provide that, we’re going to interact with the Raspberry Pi remotely, via another computer, using the VNC protocol over WiFi. This is what is sometimes referred to as ‘headless’ operation. With only the compact Pi needed, the entire rig is no longer tied to your computer by wires. It could be deployed beyond the reach of typical leads, or even tucked into a sealed cabinet. As many of BitScope’s products are designed with the idea of remote data logging in mind, with devices having many more channels than the Micro, it is well suited to this type of usage. A USB power supply or even a USB Features • Computer-controlled, isolated electronic test and measurement gear • Includes a 14V, 1A current-limited adjustable power supply, oscilloscope with two analog and six digital channels, and arbitrary waveform generator • Remote access capability • Easy screenshots for recording observations and measurements • Capable of data logging battery pack supplies power to the Raspberry Pi and the attached devices (power supply & scope). Communications over WiFi ensures that the equipment under test is safely isolated from your computer. A good-quality USB power supply will ensure that the supply to the Pi is floating with respect to Earth, while providing all the power that the Pi and the attached hardware need. So in summary, our configuration has the BitScope Micro and Mini Digital PSU plugged into the USB ports on a Raspberry Pi. Rather than connecting the Pi to a monitor and controlling it with a keyboard and mouse, the Raspberry Pi runs a program called VNC Server. This allows other computers to connect via WiFi (or LAN) and operate the Pi as if you are sitting in front of it with a monitor, keyboard and mouse attached. This arrangement is not difficult to set up if you follow our steps. We also have a few useful tips for using such a configuration. The Raspberry Pi Raspberry Pi single-board computers are quite amazing for their price. They’re powerful but almost disposable! That’s why they make an excellent choice for interacting with equipment that might be prone to let the smoke out of any test gear that they’re connected to. We used a Raspberry Pi 3B+ for our testing, although just about any variant with WiFi will work. The Pi Zero variants are cheaper, but you might also need to fork out for an adaptor or hub Hidden inside the black case above left is our Raspberry Pi, which forms the heart of this project. At lower right is the Bitscope Micro, protected from accidental shorts by its clear heatshrink sleeve. At top right is our brand new Mini Digital Power Supply – so new it also appears in this issue (see page 38). siliconchip.com.au Australia’s electronics magazine February 2021  81 Screen1 (left): if you haven’t used Raspbian (or Raspberry Pi OS as newer versions are named), you should find that it is not too different in operation to Windows. But note that instead of a “Start” menu, it has the Raspberry icon in the top left corner. Screen2 (below): the only change we’ve made from the Raspberry Pi’s Configuration System defaults is to give it a unique hostname. You can also experiment with the resolution so that the VNC viewer window is a useful size. to connect USB devices. If you’re only using the ’scope feature, then a simple USB OTG adapter might be enough. Naturally, you will need the WiFi version to go wireless. If you already have a Pi set up, then you can skip the operating system installation and look at what settings are needed to allow VNC to work. The Raspberry Pi needs to have an operating system installed on a microSD card, which you can load onto a blank card yourself, or you can buy ‘pre-flashed’ cards. Look for a ‘NOOBS’ (New Out Of Box Software, see parts list) SD card, or follow instructions for creating such a card on the Raspberry Pi website (www.raspberrypi. org/documentation/installation/ installing-images/README.md). Connect up the keyboard, mouse and monitor to perform the initial setup. Then connect a suitable power Screen3: during setup, we recommend enabling the VNC and SSH interfaces. VNC is needed to allow connections from the remote VNC viewer, while SSH can be used to access a terminal remotely and also interface to SCP programs for easy file transfers. 82 Silicon Chip supply. Allow the Pi to boot up to the desktop screen, as shown in Screen1. The keyboard, mouse and monitor only need to be connected during the initial setup. After this, remote access makes the extra gear unnecessary. Setting it up You might be prompted to enter locale information (eg, your country of residence) after booting it up. Next, connect to a WiFi network using the icon at top right. You can use an Ethernet connection if you prefer, although you won’t get the same degree of isolation. Then at top left, open Pi icon –> Preferences –> Raspberry Pi Configuration (Screen2). To use VNC, under Interfaces, you will need to set VNC to Enable (Screen3). SSH is also a handy interface to enable. Another useful item to set (under System) is to change the hostname; we set ours to ‘bitscope’. This will give your Pi a distinct name which allows it to be easily found instead of using its IP address. See our screenshots to check your settings; we didn’t need to change anything else, but your setup might be different if it isn’t a fresh install. In case the hostname method doesn’t work, it’s a good idea to note Screen4: installing the Processing IDE requires the use of the terminal, but can be completed with a single command. The script downloads the necessary files and installs them. Once complete, the Processing menu item should become available. Australia’s electronics magazine siliconchip.com.au The Bitscope Micro USB Oscilloscope and Analyser COMPENSATED ATTENUATORS HIGH SPEED A/D CONVERTERS CHA LED RANGE CONTROL & WAVEFORM SAMPLING LED GENERATOR POWER LED USB • CHB LEDLED POWER SIGNAL I/O • • • • • • • CHB LED DATA LED INPUT BUFFERS COMPARATORS AND SWITCHES CPU & DSP USB COMMS • • • • 20MHz bandwidth 40MSps logic capture 2 analog scope channels 2 analog comparator channels 6 logic/protocol analyser channels 8 & 12 bit native analog sample resolution Decodes serial, SPI, I2C, CAN and more Windows, Linux, Mac OS & Raspberry Pi Built-in analog waveform & clock generators User programmable, C/C++, Python, VM API Tiny, lightweight (14g) and water resistant Standard oscilloscope probe adaptors available The Australian-designed and produced Bitscope Micro USB Oscilloscope and Analyser is around 120mm long (seen here about life size), so doesn’t take up much space at all. Our unit came with a full complement of short, colour-coded test leads, with a grabber at one end and a header to suit the I/O breakout at the other. As seen above, the pins are marked on the back of the PCB, with the green and yellow CHA and CHB designations matching the trace colours in the DSO application. It is available direct from Bitscope (www.bitscope.com) or from numerous resellers. the IP address; it can usually be found by hovering your mouse pointer over the WiFi (or LAN) icon. We also set the display resolution (using the Set Resolution button under System) to something quite low so that the Pi’s window is not full of empty space. The DSO app runs at around 700x500 pixels, while the Mini Digital PSU is only 480x320 when calibration is not running. We’ll finish setting up the Pi while we’re at it, but the remainder can also be done via the VNC interface later, if you like. The Pi has its own web browser, so you can directly download software via WiFi onto the Pi if you have an Internet connection. You can download the BitScope apps f r o m h t t p : / / m y. b i t s c o p e . c o m / download/?p=download&f=APDA Start with the DSO app. Download the .deb file to your Raspberry Pi and run it. If prompted, the default username and password for the Pi are “pi” and “raspberry”. This should create a menu item for BitScope DSO under the Program- ming sub-menu; you can add a shortcut to the desktop by right-clicking the item and selecting “Add to desktop”. The other BitScope apps are installed similarly. There are many features to the BitScope DSO app; to try them, plug in the Micro and start the app. Press the SETUP button and select a USB port. Our unit appeared as /dev/ttyUSB0 and did not need any drivers to be installed. Then press the POWER button to access the DSO screen. We’ll have a closer look at some of the BitScope apps, including DSO, a bit later. Installing Processing Screen5: since Processing is available on numerous platforms, our Mini Digital PSU software can even run on the Raspberry Pi. There is room on the virtual screen to set up the DSO and PSU apps next to each other for a complete Virtual Workbench. siliconchip.com.au Australia’s electronics magazine To use the Mini Digital PSU, you will need the Processing application. There are a few ways to achieve this, as listed on the Processing page at https:// pi.processing.org/download/ One option is a downloadable image file which can be written to an SD card (although this appears to be a few years old and thus might not support the Raspberry Pi 4 variants). But we suggest that you use the simple terminal command to download and install it, if it is not already. Open a Terminal window by pressing Ctrl-Alt-T (or via the Pi’s menu, under Accessories) and enter the command: curl https://processing.org/ download/install-arm.sh | sudo sh February 2021  83 Screen6: with a suitable hostname for our Raspberry Pi, we can access it from the VNC Viewer app by simply typing that name in the address bar. This is far easier than using the IP address, especially if you are using DHCP rather than static IP addresses. (The vertical bar symbol can usually be found on the backslash key). This will download and install Processing – see Screen4. Like BitScope DSO, a menu item will appear under the Programming submenu. To use the Mini Digital PSU, you will also need our sketch file. You could use the browser to download this directly on the Raspberry Pi, or copy it to a USB stick. But we’ll show you another method after we set up our PC to access the Pi remotely. Once you have Processing and the sketch file installed, fire up the sketch and check that you get a display like that shown in Screen5. You can now shut down your Pi, disconnect the keyboard, mouse and monitor and then power it back up, so that it can be accessed remotely. ating systems (but they don’t all use the same protocols). You could even use an old Android phone to connect to the Pi, making for a compact, portable display as RealVNC also has an Android port. Download and install the VNC viewer and run the program. Type the Pi’s hostname or IP address in the address bar (Screen6) and press Enter. You will be prompted for a username and pass- word; the defaults for these are “pi” and “raspberry”. At this point, you should have a view and control over the Pi’s desktop and can run the apps as needed, almost as though they are running on the local machine. We also need a program to allow us to get files on and off the Pi easily. One important use for this is to download screenshots, which are saved as .png files to the /home/pi folder when you press the Print Screen key. As we enabled SSH earlier, we can connect to the Pi using a terminal emulator such as TeraTerm. But SSH also provides a way to move files using an SCP (secure copy protocol) program. SCP uses an SSH session to transfer files over a network link. We use WinSCP (https://winscp.net/ eng/index.php) on Windows computers, but a cross-platform alternative is FileZilla (https://filezilla-project.org/). Use the same hostname/IP address, username and password combination as for VNC. The default SSH port number 22 should work, unless that has been changed on your Pi – see Screen7. Once logged in, a pair of windows for local and remote filesystems is shown. Files can be copied and pasted using the usual shortcuts. The version we use even allows files to be copied and pasted directly into other windows, such as native file explorers. PC programs You need a VNC viewer on your PC. The pre-installed Raspberry Pi VNC server (which we activated earlier with the VNC option) is designed to work with the RealVNC viewer, which can be downloaded for free from www. realvnc.com/en/connect/download/ viewer/ But you are not limited to a PC, or RealVNC’s software. Many different VNC clients are available which run on various oper84 Silicon Chip Screen7: using WinSCP for remote file access requires logging into the remote computer using its credentials; in this case, the Raspberry Pi. We found that we were also able to use the hostname to make this connection. Australia’s electronics magazine siliconchip.com.au Screen8: setting up the BitScope Micro is not much more involved than plugging the unit in and selecting its serial port. The settings shown here are typical for most Linux distributions, including those on the Raspberry Pi. We didn’t even need to install drivers. BitScope apps Once you have connected to the BitScope (Screen8), the DSO app presents a screen that looks as you might expect for a ‘scope (Screen9), with most of the window taken up by the waveform display. Horizontal (time) controls are at lower left, followed by the vertical (voltage) controls to the right. Unlike a desktop unit, many of the displays have alternative, hidden functions which can be accessed by either clicking on the button or by right-clicking for a menu. Usually, the left mouse button will toggle between the most recent selections made from the right-click menu. The mixed-signal options can be viewed by clicking on the buttons to the right of the main display, while the small display at upper left controlling both the trigger and waveform generator. These have unusual but intuitive slider controls. The hidden slider controls can be used by pressing down on you mouse button over the control and then moving up/down or left/right. The control’s value will change and is fixed by releasing the mouse button. We also looked at the Logic app (Screen10), as we figured this would siliconchip.com.au be another one we would be likely to use. Like the DSO app, there are numerous options, including automatic decoding of I2C, SPI, CAN and UART. The sampling duration and frequency can be set, as well as the pretrigger period (as a percentage of the duration). It appears that the buffer holds around 6000 samples, which is quite small, but sufficient for many applications. A good selection of trigger options makes it easy to capture the important parts of the data and thus conserve the limited sample space. Once we worked out where all the settings were located, we found it easy to trigger and view the decoded data, as this occurs automatically. You might be thinking that the BitScope Micro would make an excellent data logger with the right software. Fortunately, the BitScope Chart application provides data logging and virtual chart features. The Chart app can derive values such as frequency, duty cycle and RMS values and log to the SD card in CSV format, allowing the data to be easily exported (using SCP for file transfer) and analysed in a spreadsheet program. We can’t possibly cover all of its features, but there are links to tutorial videos and other educational articles at www.bitscope.com/product/ Screen9: the BitScope DSO app is fairly intuitive and works much like a benchtop ‘scope, although there are more options, including some hidden in rightclick menus. The function generator at upper left is included in the DSO app, so you can easily feed test signals to your circuitry. Australia’s electronics magazine February 2021  85 Parts list – Virtual Workbench 1 Raspberry Pi (eg, 3B+ or 4B) [Jaycar XC9001, Altronics Z6302G] 1 SD card with Rapsbian operating system installed [eg Jaycar XC9030, Altronics D0313A; see text] 1 power supply to suit the Raspberry Pi 1 BitScope Micro USB Oscilloscope (or similar model) 1 Mini Digital PSU (see construction article starting on page 38) 1 keyboard, mouse & monitor set (for setup only) Screen10: the Logic app provides logic analyser functions and can automatically decode SPI, I2C, CAN and UART, with several extra options available for each protocol. BS05/ Since the BitScope Micro (and its larger brethren) all use a simple serial protocol, it would be very easy to write a custom application to add more features. The folks at BitScope are already onto this and have written the BitLib software library to allow custom applications to be created using C/C++, Python and Pascal. For more information, see www.bitscope.com/software/library/ BitScope server Some BitScope hardware natively supports an Ethernet connection; you might have seen this option appear while setting up some of the apps. This means that with a VPN or DNS software, it’s possible to connect to a BitScope device over the internet. BitScope keeps a Model 325 available online that you can try out, although, at the time of writing, it was not working. You can find out about this at www.bitscope.com/ software/?p=demo or access it by connecting to sydney.bitscope.com via the DSO application. The Model 325 has a native Ethernet connection, but the Micro does not. However, it can still be made accessible over Ethernet through the BitScope Server app. We tested this on our Raspberry Pi too. Like the other programs, the Server can be installed by downloading and running the .deb package. It won’t appear on the Pi’s menu as it is not a GUI application. Instead, it is started via the terminal. The version we tried appears to be an early beta version, so the options to run as a daemon (background ser86 Silicon Chip vice) have not yet been implemented. Still, we were able to start the Server by opening a terminal and running the “bitscope-server” command. Leave the terminal open to allow the Server program to continue to run in the background. Going back to the DSO app on our PC (where we are running the VNC client), we used the setup page to point it to an Ethernet device at “UDP:bitscope” (Screen11), as per the hostname set earlier; an IP address should work too. This option has the advantage of running the applications natively on what would typically be a faster PC than a Raspberry Pi. There’s also the option of being able to access the BitScope device from multiple machines, although we found the results were (unsurprisingly) unpredictable when we tried to do this from two PCs at the same time. Conclusion It’s incredible what is now possible with small computers like the Raspberry Pi, and we are already making good use of our Virtual Workbench. Since we often require ’scope grabs for printing in the magazine, having a USB oscilloscope makes that a bit easier. One of the nice things about the BitScope range is that even if the hardware doesn’t have a feature that you want, it is often possible to do it with other apps or through the scripting and library features. Being able to operate a scope and power supply over WiFi has benefits beyond our cramped home workshops. It is handy in any case where isolation is essential, or the device under test is far away from your bench. We’re sure that we’ll make use of this Workbench even when we have much more expensive pieces of equipment at hand! SC Screen11: the BitScope Server program runs in the background and makes the USB-connected BitScope Micro available over Ethernet (or WiFi). Since we have set up our Pi with the “bitscope” hostname, it can be easily found on our network. Australia’s electronics magazine siliconchip.com.au