Build Circuits With Rich – DIY Oscilloscope (O-Scope) Project Part 3
Foundation
Romans 10:9 KJV
“That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.”
Welcome to Part 3
Welcome back to the DSO138 oscilloscope kit build!
In Part 3, we continue assembling the board and make some great progress. This lesson is mostly hands-on, so there are no major theory sections or equations this time — just real electronics work at the bench.
Watch the Video:
What We Installed
In this video, we installed:
Tactile push-button switches
Ceramic capacitors
LED indicator
Connector J9
PNP and NPN transistors
Voltage regulators
Missed switch SW8 — caught and installed at the end
Switch Installation
The first parts installed were the small tactile push-button switches. These switches are used for the oscilloscope controls.
The switches fit into the board in a specific direction, so the board layout helps guide the installation. After soldering, I checked that the buttons still clicked properly.
Tip: After soldering a switch, press it a few times to make sure it still moves and clicks correctly.
Soldering Tips
During the switch installation, I used a little flux to help the solder flow better.
Flux is helpful when solder does not want to stick cleanly to the joint.
Helpful reminders:
Use a clean soldering iron tip.
Use flux when needed.
Try to make shiny, clean solder joints.
Trim leads carefully after soldering.
Watch for small clipped leads that could short something on the board.
I also used smaller, sharper cutters in this video. These worked much better for trimming small component leads close to the board.
Ceramic Capacitors
Next, we moved on to the ceramic capacitors. These are the small disc-style capacitors used throughout the board.
One important marking in this build was:
104
A capacitor marked 104 is:
100,000 pF = 0.1 µF
Some of the other capacitors had simple markings like 22, which indicates a 22 pF capacitor.
These ceramic capacitors are not polarized, so they do not have a positive or negative side. They can be installed either direction electrically.
I still tried to line up the markings in the same direction to keep the board looking neat.
Capacitor Placement Tips
When installing the ceramic capacitors:
Check each capacitor value before installing it.
Look carefully at board labels such as C1, C9, C17, etc.
Use the manual and board silkscreen together.
Bend the leads slightly so the part stays in place while soldering.
Make sure bent leads do not touch other pads or parts.
Installing several small capacitors can take a while, but once you get into a rhythm, it goes pretty smoothly.
LED Installation
After the ceramic capacitors, we installed the LED labeled D3.
This LED is polarized, so it must be installed in the correct direction.
Ways to identify LED polarity:
The longer lead is usually the anode, or positive side.
The shorter lead is usually the cathode, or negative side.
The flat side on the LED body usually marks the cathode.
The larger internal metal piece is usually the cathode side.
For this kit, the instructions indicated that the longer lead goes into the square pad on the PCB. The square pad was also marked positive on the board.
Connector J9
Next, we installed connector J9.
This part required care because the plastic body can melt if too much heat is applied for too long.
With plastic connectors, there is a balance:
Too little heat can create a cold solder joint.
Too much heat can melt the plastic and shift the pins.
I used a quick tack-soldering approach to hold the part in place, then soldered the rest of the pins carefully.
Transistors
We then moved on to the transistors. This step requires extra attention because the kit uses different transistor types.
In this video, we identified and installed:
S8550 PNP transistor
S9014 NPN transistor
The board silkscreen shows the outline of the transistor body, including the flat side. This helps with orientation.
Important: Always double-check the part number before soldering transistors. Installing the wrong transistor or installing it backward can keep the circuit from working and could possibly damage parts.
Voltage Regulators
The next parts installed were the voltage regulators. These look similar to small transistors, so it is important not to mix them up.
In this part of the build, we installed:
79L05 regulator at U4
78L05 regulator at U5
The 78L05 and 79L05 look very similar, but they are not the same part.
Take your time and check the part markings before soldering.
Real-World Mistake: Missed Switch SW8
After wrapping up the main build section, I found one extra switch while cleaning up the bench.
That led me back to the manual, where I realized I had missed switch SW8.
Thankfully, this was an easy mistake to fix.
This is a good reminder: real builds are not always perfect. Take your time, check your manual, and look over the board before moving on.
What’s Next?
In the next part of the oscilloscope build, we will continue with more components, including:
Trimmer capacitors
Power inductor
Electrolytic capacitors
Additional connectors
Power-up checks and testing
Once the board is fully assembled, we will need to check voltages and begin testing the oscilloscope.
Final Thoughts
This build is really starting to come together.
Part 3 included a lot of hands-on soldering, careful part identification, and a few real-world lessons along the way.
If you are following along, take your time, double-check each part, and do not worry if everything is not perfect.
The goal is to learn, build, and improve as we go.
Keep building. Keep learning. And as always…
Time to go to the lab.
Thanks for spending time with me on this oscilloscope build. I’ll see you in Part 4!
Want more electronics lessons?
For more beginner-friendly electronics lessons, circuit walkthroughs, and hands-on breadboard builds, visit:
https://buildcircuitswithrich.com
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