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[Sharing /User Voice] Disassembling Review and Application Case of DS211 Mini Oscilloscope

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发表于 2016-10-31 15:47:09 | 显示全部楼层 |阅读模式
The DS211 Oscilloscope Kitincludes 1 DS211 mini oscilloscope, 1 X1 probe analyzer,and 1 copy of Safety Instructions.
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The charger is still not partof the standard kit. User may use 5V USB cable for charging, and it is no adamant about using an original charger.
Now let’s take a look atthe exterior. The exterior design does not differ very much from that of DS201. On the side of the device, a ring of white line divides the external shell intoa design resembling a sandwich, with the white linebetween two black ones. On the frontal shell of the device, there is a 2.8-inchcolor LCD screen. On the right side of the frontal shell, there are a set of 6white keys. The markings of DS211 mini oscilloscope are complete and moresimplistic.

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The brand name and logo are printed on the back of the device. And there are alsologos of certifications such as CC (Creative Commons), CE and FCC markings,etc.

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On the left bottom, there isa striking warning mark. It states that the maximum input voltage is ±40V, and exceeding voltage would damage the device.
On the upper right side of the device, there is a tumbleswitch, while at the lower side of the switch, there is the mouldpressing word “OFF”.

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On the left side of the device, there are signal input and output channels,as well as a Micro USB port. On the shell of the device, there are mould pressing texts such as INP, OUT and USB.

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Size of the Oscilloscope:

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Concerning the material of the external shell, except for thefront-panel, which is made of glass, the other parts, from inside to outside,are made of quality engineering plastic of its original color and the surfaces of these parts are matte. I don’t mean that plastic is no good. Plastic shell isbetter than a metallic one in terms of insulation. Especially when the deviceis used in a high-voltage situation, it is of greater safety. After all, thedevice is a measurement instrument, and safety is the top priority.

The copy of Safety Instructions is bilingual,in both Chinese and English. Before using the device, please read it carefully.No printed copy of user manual is supplied. In Safety Instructions, it suggests that users may go to the official forumof Mini DSO to download a more detailed manual. There is detailed informationin e-versions for the previous products on the forum, even including circuitdiagrams and source codes of firmware. Since e-Design upholds the spirit ofopen source and sharing, its application layer is open source.

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The standard kit includes 1 probe analyzer whose model is DS-T01, at X1 magnification.The special MCX is applied to match the main body of the device.

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One IC protector is supplied,with a number of colorful rings for identification.

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The first image displayed on the screen when thedevice is turned on indicates that the firmware version is V1.2.

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With in 2 seconds after booting,the screen displays the interface of normal operation.

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If you are a first-time user, you may gradually understand its functionsthrough checking its menu. On the upper, lower and right side of the screen,similar to the design of DS201, there are indicative texts and color blocks offunctions, but there are still evident differences. The main menu is on theright sidebar. Press the “up” and “down” keys, and you may choose the menu options. If you press the “M” key, a sub-menu of secondaryfunctions would pop up. And you may press the “left” and “right” keys to alterparameters accordingly. In the upper and lower sidebars, at the color blockscorresponding to the colors of the main menu, the configuration parameters areindicated. This is a very smart design.

T12.png

Menu of the Y Axis

Long press the “>||”key, and you may save and alter the booting default parameters.

T13.png

Menu of the X Axis

T14.png

Menu of Trigger Control

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Menu of Project Measurement

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Menuof Calculation Channels

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Menu for Saving and Loading
The screenshot of this menu cannot be captured. I can only take photo of it.

T18.png

Menu of Signal Generator

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Menu of System Configuration

T20.png

There are 8 menus in the right sidebar. The upper sidebar has 6indication blocks of parameters, while the lower sidebar has 4.

DS211’s display layout and items for parameterindication are arranged in a very reasonable way, and there are richerfunctions, which are more than expected.

On the basis of the above-mentioned functions of the keys, I have editeda comparison table of menu functions.

The device has a 8M built-in USB flash drive which can be seen when itis connected to the computer. The functions of the flash drive have nothingdifferent from those of an ordinary USB drive.

T22.png

Turn on the device while pressing the “-“ key or “M”, key  andyou will enter the interface of system modification (the DFU mode). Whenconnected to the computer via a USB cable, it is very easy to conduct system modification. Since the application layer is shared publicly and open source,user enjoys much greater playability

T23.jpg

The DFU version displayed in the interface isv3.61D, and there is a reminder in English below: Copy and paste the  hex or bin firmware files into the virtualUSB drive.

The functions of the DS211 front panel are also made clear now, and theyare listed in the table below.

T24.jpg

Actual Measurement
When the probe is connected, you may touch the probe head to produce a50Hz interference signal, and make adjustments on the relevant menu items, soas to ensure that the displayed waveform is easy to check.

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When you notice that the menu of the X axis popsup, there would be a red bar appearing at the bottom of the screen. It turnsout that this is an indicative bar that shows the status of waveform saving andthe displacement of the X axis of the current window.

DS211 provides a function of windowdisplacement, namely:
The location of the horizontal window can be adjusted to move left orright with indication; and the moving range is the memory depth, as shown inthe figure above. Vertical displacement is adjustable to move up or down withindication; and the moving range is between the upper and lower limits of movingthe trigger point towards the window.

The physical resolution of DS211’s screen is 320*240, with a sufficient visualangle and brightness. Let’s partially zoom in and check.
T27.jpg

I. Several Simple Tests for the Mini Oscilloscope
1. Noise
Without connecting probeanalyzer, tune the sensitivity of the Y axis to 20mV/V, which is the highestlevel, and use the Vpp measurement item, the reading is in a range between2.4mV to 4.0mV, which is a very good record.
T28.png

2. The Lowest Voltage Resolution
Still set the sensitivity at highest level 20mV/V. At this moment, thefullness is 4V, namely ±80mV. It can be found that the minimum stepping for thefluctuations of amplitudereading is 0.8mV, a value <1mV, equivalent to the resolution of a three-digit multimeter, whichis sufficient for the testing of general applications.
3. Response Speed
When testing continuous signals, the screen display is in real-time response to thetest, and you may feel no latency.
I performed a capture test onthe burst pulse signal. The method is to set the trigger mode of the device assingle trigger, and then continuously input 1us or 2us narrow burst pulses in amanner of repetitive single trigger. The duration for trigger usually lasts 0to 2 seconds, occasionally it may last more than 2 seconds. On this basis, themaximum capture window is about 3 seconds. Meanwhile, you can see that the zeropoint of the X axis is displaced from the trigger point by about 1us.
Capture of 1us pulse:
T29.png

Capture of 2us pulse:
T30.png

4. Bandwidth Test
The built-in signal generator of the mini oscilloscopecan generate a sine wave with a maximum frequency of 20 KHz, as well as asquare wave with a frequency ranging from 10 Hz to 1 MHz. You may test the square wave generated by itself for bandwidth. To do this test, you just needto insert two X1 probe respectively into the Input and Output ports, and theninterconnect them. The display of 200KHz square wave of the signal generator inan actual test is shown below:

T31.jpg

The 200 KHz square wave can be displayed like this, with flat tops bothup and down. That means there is no problem with the 200 KHz sine wave, and thebandwidth of the mini oscilloscope is definitely higher than 200 KHz. However,the positive and negative pulse widths are a bit asymmetric,which means the bandwidth may not be very high.
Previously, in the chapter of “II Functions”, thereare images of actual tests on the square waves with frequencies of 10 KHz, 100KHz and 500 KHz. Here, I would not repost the imagesagain.

5. Sleep and Auto-off Functions
I tested the automatic sleep and automatic power-off functions, andfound that the USB drive connection can be retained if the sleep function ofthe device is enabled rather than the automatic power-off function; whereas when the USB cable is plucked, the timing would go on till automatic power-offis performed.

II.Simple Tests with the mini Oscilloscope
1.  Testing the Booster Circuit of Portable Power Supply
The booster circuit insidethe portable power supply increases the 4V voltage up to 5V for the USB port.Now I would test its waveform:

T32.jpg
T33.jpg

It can be seen that the waveform which is supposed to be a square waveis actually quite complicated.

2.  Testing the Electric Capacity Waveform of a Multimeter
The electric capacity mode for ordinary multimeters employs Wien-bridge oscillator to generate a signal of sinewave with a stable frequency and amplitude for testing, and the oscilloscopetests the electric capacity of the capacitor based on the capacitive reactance. The tested multimeter is my own DT9203. The actual testedwaveform is shown below:
T34.jpg
T35.jpg

We can see that the frequency is relatively stable, always at a level of159 Hz, but there is a bit of peak clipping distortionat the bottom of the waveform. And this is a common problem for the oscilloscopes equipped with the Wien-bridge oscillators.

Conclusion
Range of Application:
The main usage occasions of this mini oscilloscope have already compiledby somebody else, so I just copy and post the file here:
A. On-the-spot examination and repair (AC/DC switch power supplies or inverters, elevators and fire service gears for buildings, industrial control circuits);
B. Hardware examination and repair, and software debugging for communication interface circuits such as RS232, RS485, I2C and CAN, driver circuits for LED display and keyboards, and brushless motors,;
C. Examination and repair for audio devices and circuits, electronic toys and remote control models, and automobile electronic circuits;
D. School teaching, student practice and extracurricular work of electronic interests;
E. Application occasions that require the observation of gradual signal changes (such as the shaking of relays and switch contacts, the charging and discharging curves of batteries, transient responses for the load of regulated power supply, and measurement of properties of temperature sensors)
F. Electronic circuits related to power supply (SCR voltage regulator, power factor compensation, energy efficient electronic lamp, street lamp driver circuits for sodium lamps, dysprosium lamps, mercury lamps, and xenon lamps, etc)
G. The device is also used as a function signal generator.

ApplicationCase
Waveform comparison, waveform calculation and waveform mirroringcomparison of DS211 mini oscilloscope, are a few functions that are common foroscilloscopes.
Comparison of two waveforms during measurement
T36.jpg
T37.jpg

Conduct waveform calculation with the two waveforms in the image above
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Mirroring comparison of a single waveform
T40.jpg

With these functions, undoubtedly, testing and calculating speed can be improved.And these functions have provided much convenience for comparison andverification.

Case 1: Quality determination for crystaloscillators
Many people may ask: How can we judge if acrystal oscillator is good or not? Let me give an example. The method todetermine if a crystal oscillator is good or bad with a multimeter is to testthe voltages between the two pins of the crystal oscillator, then the testermay judge the quality of the crystal oscillator by telling the voltagedifference between the two pins. This method may only offer a general conclusion of whether the oscillator is good. In fact, the answer is uncertain.If you want a genuine determination, you need to see if the oscillator has awaveform, in this way you would be genuinely able to tell if a crystaloscillator is good or not.
This is a waveform. It is the image of a good clock oscillator, with a frequency of 32.768 KHz (foryour reference). Clock oscillators are widely used in many fields. You may findone in almost all electronic devices (such as computer motherboards, electronichosts, electronic watches, and multimeters, etc). So, I decide to put thistypical case here.
T41.jpg

Case 2: Debugging of Shottkydiodes in a state of semi-destruction for switching power supplies
In a state of no-load, for switching power supplies and mobile phone power banks, the tester shall judge if there are pulse signals at the output end of Shottky diodes.
Switching power supplies have a large ownership among forum buddies. Therefore, the probability of malfunction would be very high. These power supplies, in a state of no-load, would all feature a standby pulse signal voltage on the diodes ofthe output end.
The image below is the normal operating waveform of the peak protection circuit ofa power supply (for your reference).
The primary time in the image is the duration required by the breakover operation of rectifying diode. At this moment, there is no peakvoltage generated.
T42.jpg

The secondary time is the cut-offtime of the rectifying diode. At this moment, the peak surge voltage is eliminated through the absorption of the peak protection circuit.
T43.jpg

The unfolded image of the waveform of the secondary time
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