Assemble the final system
Follow the student handout to build, test and document this stage of the water-quality system.
Prepared lesson material. Start this task when your teacher introduces it; it is not currently assigned homework.
For this lesson
Read the handout text online
Lesson 13: Permanent Assembly and Strain Relief
Soldering, insulation, and harness inspection
Grade 9 MYP Design | From USB to Field System
| Name: __________________ | Class / team: __________________ | Date: __________________ |
| Today’s goals • Make a clean electrical joint. • Insulate conductors and protect PCB pads from movement. • Build a traceable, serviceable harness. |
Key vocabulary
| Term | Working definition |
| tinning | |
| wetting | |
| cold joint | |
| solder bridge | |
| strain relief | |
| pigtail | |
| ferrule | |
| heat shrink | |
| service loop |
| Soldering safety Circuit unpowered. Safety glasses on. Iron returns to holder whenever it is not touching the work. Use ventilation. Wash hands after handling leaded solder. |
1. Quality rubric
| Feature | Good | Needs correction |
| Wire preparation | Correct strip length; strands twisted; light tinning | Loose strands; excessive stripped copper; large solder spike |
| Joint | Solder wets wire and pad; smooth fillet | Ball/blob, cold grainy surface, incomplete wetting |
| Bridges | No contact with adjacent pads | Solder bridge or loose strand |
| Insulation | Heat shrink covers exposed conductor | Bare resistor legs or solder exposed |
| Strain relief | Cable secured by insulation/clamp/tie | Force carried by pad or solder joint |
| Serviceability | Labels and connectors allow tracing/removal | Unlabelled permanent bundle |
2. Practice-joint sign-off
| Practice | Electrical continuity | No short | Mechanical inspection | Teacher initials |
| 1 | ||||
| 2 |
3. Harness plan
| Connection | Wire color/label | Connector or solder method | Strain relief location |
| 5V | |||
| GND | |||
| GPIO1 EC | |||
| GPIO2 turbidity divider | |||
| GPIO4 temperature |
4. Final inspection
☐ Battery disconnected during assembly.
☐ No exposed positive conductor.
☐ No solder bridge between adjacent pads.
☐ Divider resistors and legs are insulated.
☐ Screw-terminal stranded wires use appropriate ferrules where required.
☐ Cable ties/clamps carry movement, not PCB pads.
☐ Every connection can be traced to the netlist.
☐ Continuity and no-short checks completed before power.
5. Reflection
Why is a solder joint not a strain-relief system? Describe how your build handles movement.
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