If you’re looking for a portable oscilloscope for field troubleshooting or for demonstrations, look at the Micsig TO series. Here’s my take on the four-channel 300 MHz variant, TO3004.
The Micsig TO3004 oscilloscope (Figure 1) is an 8-bit, four-channel, tablet-sized portable oscilloscope that’s also available with 100 MHz and 200 MHz varieties with two or four channels. The high-resolution 10.1-inch color touchscreen lets you control all functions using slide-out menus. The operating system is Android-based. Closing the oscilloscope application provides access to many other high-level Android apps, such as folders for storing screen captures and setups.
The models range from $639 to $1,239, depending on channel count and bandwidth. Micsig also sells compatible AC/DC current probes (up to 100 MHz bandwidth) and a Rogowski probe. The company recently announced an upgraded high-voltage differential probe. Soft or hard cases are also available.
Controls and specifications
The various setup controls simply slide out from the top, bottom, and right side of the oscilloscope’s touchscreen. Tapping the Home icon (lower left) takes you to the home screen and the built-in Android apps. Tapping the oscilloscope icon gets you back. If you’re in one of the apps, swiping up from the bottom and tapping the Stop icon (a black square) takes you back to Home. Tapping the Back icon returns you to the previous screen. This video gives you a quick overview of the screen operations.
The highest sample rate is 2 Gsa/sec, and the maximum memory depth is 220 Msa. This large memory depth lets you easily capture intermittent events. The oscilloscope has a waveform capture rate of up to 300 k waveforms/sec. The built-in 7500 mAh lithium battery is rated for over four hours and includes a physical on-off switch for safety and to avoid “dark current” from depleting the battery while stored. The side handle and lightweight (4.2 pounds, 1.9 kg) make it easy to carry.
The top slide down panel includes most of the scope setup controls. Figure 2 shows the automatic measurements, and Figure 3 shows the trigger styles.
The stock unit includes several bus decoding presets, including RS-232/422/485, UART, CAN, CAN FD, LIN, I2C, and more. Decoded text may be saved in CSV format for additional analysis. Interfaces include Wi-Fi, USB 3.0/2.0 Host, USB Type-C, ground tab, HDMI port, and trigger output.
Vertical, trigger level, and channel selection are found along the right side (Figure 4). Horizontal controls and cursors are along the bottom. System controls, trigger presets, save/load, etc., are found along the top.
The oscilloscope includes a hardware digital filter with adjustable low-pass and high-pass filters as low as 30 Hz (low pass) or 20 MHz (high pass) for filtering out noise. On the 200 MHz and 300 MHz variants, you can switch input impedance from 1 MΩ or 50 Ω.
You can remotely control the oscilloscope using SCPI commands through its USB port or even through mobile apps for Android, iOS, or PC software. The instrument supports screenshot capture, video recording, and waveform data saving into a USB flash drive or its built-in 32 GB RAM memory.
Advanced math and FFT
Swiping up on the channels panel reveals the Math selections. Swiping left on the Math channel opens the Math panel (Figure 5). Choices include “DoubleWave” where you can use math operations on the channels, along with FFT, which opens that application. Other choices include Ax+B and Advanced Math.
Figure 6 shows a typical display of the time domain and frequency domain for a 1 MHz dc-dc converter. I believe the “dB” measurement is dBV. I didn’t see a way to change this to dBm or dBµV. Refer to the summary for more commentary.
Return home
There is a nifty control that, when tapped after swiping up from the bottom and tapping either Timebase or Level, will return the waveform to a “home” or initialized position (Figure 7). This is handy after scrolling around on the stored waveform to return to a centered position.
Screen captures
When you plug a USB flash drive into one of the USB ports (right side), you can save screen images in PNG format to the drive. If you don’t plug in a USB drive, the oscilloscope will save screen captures in its Pictures > Screenshots folder.
To transfer internally saved files to a USB drive, press the Home button (lower left on the screen), then select the Files app. You should see the USB symbol appear in the upper left of the screen to ensure it’s connected. Tap on the three bars (upper left) and scroll down to select the scope model number (ex. “TO3004_TO3004”). Select the model number, scroll down, tap Pictures, and then Screenshots.
You should see all the internal screenshots taken to date. To Select All, tap the three dots (upper right) and then Select All. To select just a few, select them by tapping each file on the screen. Tap the forked icon (left of the trash can) and then select ES File Explorer (Save to ES) in the bottom row. Now choose the path to the USB drive, then Select the destination. Copies of the internal files will be written to the USB drive.
In addition to saving screen images, you can save up to ten setup configurations and recall them using this upper dropdown menu (Figure 8). I have several setups saved for demo purposes during my seminars. You may also save and recall waveforms and pictures.
Application: dc-dc converter measurements
I used the oscilloscope to measure typical EMC areas of concern — the ringing on the onboard dc-dc converter and the processor clock. To avoid slipping and shorting something when characterizing the ringing on the dc-dc converter, I use a medium-sized H-field probe closely coupled to the switching inductor (Figure 9). This non-invasive technique prevents accidental shorting of components when using conventional scope probes.
Figure 10 shows the resulting waveform with vertical cursors to measure the ring frequency of 82 MHz. If you examine the waveform carefully, you can also see traces of a second harmonic of about 164 MHz. This 82 MHz and 164 MHz second harmonic ringing can generate radiated emissions if this ringing gets coupled to power or I/O cables.
Measuring ESD
Part of my live demonstrations includes the measurement of electrostatic discharge (ESD). I’ve had a few cases in client lab areas where ESD has upset sensitive measurements, such as false triggering in oscilloscopes.
Adding a short or small telescoping antenna to one of the channels, swiping the Level control to the left, and setting the trigger to Normal will capture ESD and freeze the waveform (Figure 11). This is handy for troubleshooting unknown ESD sources. I generally start by setting the vertical to 1 V/div and 50 Ω impedance with X1 probe selection. A time base setting of 20 ns/div to 25 ns/div is about right. By using an ordinary BBQ igniter, I can generate ESD events.
Other thoughts
I’ve been pleased with the performance and portability of the Micsig TO3004 oscilloscope and have already used it in the field and during live seminars. The HDMI port lets me show the screen on an LCD panel or projector.
The four-channel version came with four 10X 300 MHz bandwidth probes. I also have a 100 MHz current probe, which I’ll review later. The 100 MHz and 200 MHz bandwidth scopes lose some features, such as memory depth and the 50 Ω impedance setting. You’ll want to check the specification table on Micsig’s website to determine what works best for your needs.
I’m impressed with the battery life of 4+ hours. The hidden “On/Off” switch at the bottom of the right side had me puzzled for a while, because I couldn’t initially figure out how to turn on the instrument. This switch is both a safety feature when traveling as well as a method to truly “turn off” the oscilloscope, thus disallowing “dark current” to drain the battery while the oscilloscope is off.
Transferring screen captures from the scope memory to a USB drive could have been a simpler process and is not adequately explained in the manual. Just be sure to have a USB drive plugged in prior to making measurements, and you’ll be fine. I had to upgrade the software to get this to work.
As a note, the saved screen capture doesn’t appear to have an “inverse” feature that will change the background from black to white. This would tend to use black ink faster if printing a report with several captures. You’d have to use a graphics editor to negate images before printing.
The FFT function is acceptable for relative troubleshooting, but the frequency response only uses the right half of the display. For example, it appears difficult to set a specific vertical scale in 10 dB steps. Also, for EMC engineers, there’s no dBµV setting. For more serious spectral analysis, I’d recommend a dedicated spectrum analyzer.
Micsig also sells a version especially for automotive measurements with custom measurements for charging/start circuits, sensors, actuators, ignition, and network (CAN, etc.) for a little bit more.
Highly recommended if you need a decent portable oscilloscope. The U.S. distributor is Saelig — price: $1,239.
Acknowledgment
Thanks to Dr. Min Zhang, EMC consultant at MachOne Design, for pointing out the Micsig TO3004 in one of his video demos. It’s just what I needed.
