About the Oscilloscope
The DSO211 ARM oscilloscope from MakerFocus is a single-channel digital storage oscilloscope that can save recorded waveforms on 8MB internal memory. These miniature oscilloscopes fit in a shirt pocket and are perfect for troubleshooting and teaching basic digital and analog circuits. This article looks at the inner workings of a single-channel oscilloscope. If you need additional channels, consider a 2- or 4-channel oscilloscope. The menu system takes a bit of time and practice to get used to, and they do not compare in the least to a full-sized oscilloscope. But what these devices lack in features, they make up for in portability. The target audience for these devices are novices, teachers of introductory electronics, and traveling technicians who need to inspect low-voltage electronics.
Image from Amazon
Taking Apart the Oscilloscope
The back of the oscilloscope can be removed by gently prying around the seam between the bottom and center plastic pieces. As sections are freed, place something in the seam to prevent the pieces from reattaching to one another. This first step allows the easy replacement of the battery and reveals four screw heads. Further disassembly occurs after the four thermoplastic screws are removed and the front side of the case is removed with more gentle prying.
See the video below for more information.
A look inside the Oscilloscope
The main circuit board inside the oscilloscope has all components mounted on one side of the board, with the exception of the display mounted on the opposite side of the board.
|Top Side Marking||Description||Cost||More Information|
MYS 99 608
|ARM Cortex-M3 MCU||$5||Website | Datasheet|
|Triple 2-channel analog multiplexer/demultiplexer||$0.2||Datasheet|
|100 MHz, Dual High Voltage, Rail-to-rail Output Amplifier||Webpage|
|64Mb Flash Memory||$1||Datasheet|
(1) STM32F103 (Yellow)
STM32F103 Block Diagram
This ARM 32-bit Cortex-M3 based microprocessor operates at up to 72 MHz. The microcontroller can access a variety of memories (Compact Flash, SRAM, PSRAM, NOR, or NAND) memory and can directly drive 8080 or 6800 LCD screens through their parallel input interface. It has 3 12-bit, 1µs analog to digital converters and features multiple timers, up to 13 communication interfaces (I²C, USART, SPI, CAN, USB2.0, SDIO) and is largely 5V input tolerant.
This is the main integrated circuit that runs the entire oscilloscope. It interfaces directly with the LCD screen's parallel input, controls the other ICs, and performs the analog-to-digital conversion for the measurements of test circuits.
(2) MIC5239 Low Drop Out Linear Regulator (Green)
This Low Drop Out Regulator has an input range of 2.3 V - 30 V and can continuously output 500 mA as long as the input potential difference stays at least 350 mV above the output potential difference. This integrated circuit provides the current and voltage requirements of the discrete and integrated circuits on the circuit board.
(3) 4053 Triple 2-Channel Analog Multiplexer / Demultiplexer (Pink)
This integrated circuit is a triple single-pole-double-throw analog switch that allows analog and digital multiplexing and demultiplexing.
One switch Schematic Diagram
3-Channel Functional Diagram
Without circuit inspection or analysis, I cannot say the purpose of this integrated circuit in the overall design.
(4) Winbond 64 Mb Flash Memory (Purple)
The datasheet indicates that this device functions at 1.65 - 1.95 V with 4 mA active and 1 µA power-down current consumption. Data is stored on 256-byte pages that can be erased by page or en masse. The chip also supports Serial Peripheral Interface (SPI), Dual/Quad SPI, as well as Quad Peripheral Interface (QPI) at high clock frequencies, for data transfer rates that, according to the datasheet, can outperform asynchronous 8 and 16-bit parallel flash memories.
(5) SGM8302 Rail to Rail Output Amplifier (Orange)
Per the data sheet, this dual channel, unity gain operational amplifier is designed to interface integrated circuits and the outside world.
These are handy tools that cost little more than a multimeter and can provide valuable circuit insight. While they will never compete in the same markets as full featured oscilloscopes, they were never designed to. These instruments are meant to be at home in an instructor's breast pocket and a student's backpack.
I own a Tektronix MDO 3104, but I still use a portable quad-channel oscilloscope (similar to this one) when traveling, teaching, or working in harsh environments that don't require the full feature set of a mixed domain oscilloscope.