Introduction: Digital Oscilloscope Kit - DSO138

By openhardware.ro

This instructable is the result of several fortunate coincidences:

  • At first, it seems that some of my articles published here or elsewhere, have drawn attention from GearBest shop: http://www.gearbest.com/. So they offered to sponsor writing an article on one of the products that they sell.
  • Secondly, I started working recently with STM32 microcontrollers. So any project that involves working with these MCUs is very interesting to me at this time.
  • Third, this type of project was exactly what I wanted to study further. A project that involves working with a TFT screen (To see that speed in action, comparing with 8bit microcontrollers). And also working with12bit ADCs (it's interesting to me so see difference between 10bit and 12bit ADC).

So, before proceeding, I have to thank them for sending me this kit: http://www.gearbest.com/development-boards/pp_208067.html ($20.29 with free shipping, at the moment I write the article)

Over time I ordered several kits/development boards/modules from various sources, this is the first that comes with printed schematic, assembly manual and user manual. Therefore first impression was very good.

Step 1: Kit Overview

Here I put some pictures to see better what it is about.

The kit has already soldered STM32F103C8T6 microcontroller. Other SMD components must be soldered by us.

Another mention: Microcontroller is already programmed with firmware, so no need to flash after assembling.

I chose to follow the steps in the documentation.

Let's start.

Step 2: SMD Components

This is the most difficult part. Soldering SMD components by hand it is not easy, but can be done carefully.

There is a documentation page specially for this step. It was very useful for me.

Also, I think it is best to unpack one component at a time. Especially for SMD resistors.

And do not sneeze toward desk! :)

Step 3: Resistors

Things start to be more easy. But there's a catch. It's easy to make mistakes with these resistors (color-coded).

You must carefully identify each resistor(and measure with a multimeter/ohmeter); some values are mirrored versions(or very similar) of other values.

Step 4: HF-Chokes

L1, L3 and L4 inductors are easily identifiable and PCB markings are clear.

Step 5: Diodes

Same for diodes:

  • D1=1N5819
  • D2=1N4004/1N4007

Step 6: Crystal

Nothing to say at this step.

Step 7: USB Socket

USB socket is not in use with current firmware (maybe someday we will try to make our own firmware to use this port).

It is good to check we did correct soldering, pins are very close.

Step 8: Tact Switches

  • SW4 = OK
  • SW5 = Plus / Up
  • SW6 = Minus / Down
  • SW7 = Sel
  • SW8 = Reset

Step 9: Ceramic Capacitors

Easy to identify on PCB. We must be careful to markings:

0,1uF are marked 104

330pF are marked 331

120pf are marked 121

22pF are marked 22

3pf are marked 3

1pf are marked1 or i

Step 10: LED

D3 = ⌀3mm, green

We have to pay attention to polarity.

Step 11: Pin Header (for Power)

The manual mention to be mounted "Face the opening outward", so I did.

Step 12: Transistors

  • Q1 = 8550
  • Q2 = 9014

Step 13: Regulators

  • U4 = 79L05
  • U5 = 78L05

Step 14: Capacitor Trimmers

C4, C6 = 5-30pF

Step 15: Power Inductor

L2 1mH / 0.5A

Step 16: Electrolytic Capacitors

C19, C21, C22, C24, C25, C26 = 100μF

We have to pay attention to polarity.

Step 17: Power Connector

J10 - Power connector

Power Source: 9V DC (8-12V) ~ 200mA

Step 18: Pin Header (male)

  • J5 = 1 x 3 pin (UART)
  • J6 = 1 x 4 pin (SWD)

These connectors can be used to read / write firmware from STM32F103C8T6 microcontroller.

I already used J6 connector to download firmware (with a ST-LINK compatible interface).

Step 19: Pin Header (female)

  • J7, J8 = 1 x 2 pin
  • J3 = 2 x 20 pin

They are used to connect (and to fasten) TFT screen.

Step 20: Slide Switches

  • SW1 = Coupling selection : GND - AC - DC
  • SW2 = Sensitivity selection 1: 1V - 0.1V - 10mV
  • SW3 = Sensitivity selection 2: X5 - X2 - X1

Step 21: BNC Connector

J1: BNC Connector.

Step 22: Test Signal Ring

From manual:

  • "Make a small ring with a lead cut-off"
  • "Solder the ring to the two holes of J2"

Step 23: LCD Board

  • J1 = 2 x 20pin
  • J2 = 1 x 2pin
  • J3 = 1 x 2pin

"Note: Install to the side opposite to LCD panel."

Step 24: Final Check

At this stage all the components are mounted. There is another step: Short JP3 with solder.

After checking voltages in test points (according to the manual), we can short JP4 with solder permanently.

Step 25: Done.

Everything is ok... DSO138 works as it should.

Conclusions

A very interesting project. A very interesting kit.

It is not a substitute for professional DSO.

An excellent tool to learn new things.

Referring to the oscilloscopes:

  • Using DSO in general
  • Functioning principle of an Digital Oscilloscope
  • The main blocks of an Digital Oscilloscope

Power Supply is also interesting. (how to obtain +5V and -5V for TL084)

Analog Chanel block illustrate how process an analog signal for digitizing.

This kit can be used as a development board with extended possibilities in the analog field.

Firmware are partial opensource. Even so worth studying. Maybe someday one of us will develop a completely open source firmware. (also with USB capabilities)

Thanks for reading!