Problem 5
Build the TF-MCU32 card: three 100 nF locals, 4.7 µF bulk, reset, boot, SWD, LED, and button.
- Follow the TF-MCU32 card: three 100 nF locals, 4.7 µF bulk, reset, boot, SWD, LED, and button.
- One shared capacitor does not replace three local ones.
Context
A microcontroller needs more than power and ground. Reset, boot, and debug each have a job. Each supply pin needs its own nearby capacitor because the pins are not one point inside the package. SWD is the debug connector: SWDIO, SWCLK, 3.3 V, and ground.
Components on this challenge
- TF-MCU32. The training microcontroller. Each supply pin, reset, and the debug pins are separate.
- SWD. Serial Wire Debug: two signals, SWDIO and SWCLK, used to program and debug the MCU.
- Capacitor. Stores charge and supplies a short pulse of current. With a resistor it also sets a time.
- Resistor. Limits current. The voltage across it divided by its resistance is the current through it.
Complete the required schematic checks to unlock PCB Layout.
Full brief
Give each MCU supply pin its own local capacitor, add the bulk capacitor, and wire reset, boot, and the debug header as separate jobs.
How PCBGrade measures this
Board 50 × 40 mm, two layers. J1 is locked: pin 1 is 3V3 and pin 2 is GND. TF-MCU32 has no exposed pad; pitch is 1.27 mm. Each of VDD1, VDD2, and VDDA gets its own 100 nF to GND. The NRST capacitor is not one of those three. Locals are 10 nF, 100 nF, or 1 µF; only 100 nF passes. Bulk is 4.7 µF (3.9 / 4.7 / 5.6 µF are offered) and has no distance limit. NRST is 10 kΩ to 3V3 and 100 nF to GND. BOOT0 is 10 kΩ to GND; a pull-up fails that rule. The SWD header carries exactly 3V3, GND, SWDIO, and SWCLK, in any order, and not NRST. The LED is GPIO → 1 kΩ → anode → cathode to GND. The button is to GND with 10 kΩ to 3V3; a button to 3V3 fails. 10 kΩ options are 8.2 / 10 / 12 kΩ. 1 kΩ options are 820 / 1000 / 1200 Ω. Points: VDD net 4, GND net 4, NRST resistor 5, NRST capacitor 5, BOOT0 5, SWD pinout 5, LED path 2, LED resistor 3, button to GND 2, button pull-up 3, bulk 4, local value and count 3. Placement is 20, split across the three supply pins (partial credit): each local 100 nF within 4.0 mm routed of its supply pin, zones excluded, one capacitor per pin. A via barrel is 1.565 mm. Connectivity of every net is 15 and does not cap the score. A short between 3V3, GND, or any MCU net, or an unrouted 3V3 or GND, is 10 points and caps the score at 69. An open signal does not. DRC is 10 (clearance 0.20 mm, copper at least 0.50 mm from the edge). Pours are not allowed.
- schematic correctness · 45 pts
- decoupling placement · 20 pts
- PCB connectivity/completion · 25 pts
- DRC · 10 pts
- Cap 69: A short on an MCU net, or an unrouted 3V3 or GND, caps the score at 69.
- Cap 69: Copper outside the outline cannot pass, and neither can a short between nets.
Reference
TF-MCU32
Three supply pins, each with its own 100 nF. Active-low reset, SWD, one LED, one button.
- 1. VDD1. Digital supply. Own 100 nF to GND.
- 2. GND. Ground
- 3. VDD2. Digital supply. Own 100 nF to GND.
- 4. GND. Ground
- 5. VDDA. Analog supply. Own 100 nF to GND. No ferrite, no shared group.
- 6. NRST. Active-low reset. 10 kΩ to 3V3 and 100 nF to GND.
- 7. BOOT0. 10 kΩ pull-down to GND. A pull-up fails.
- 8. SWDIO. SWD data
- 9. SWCLK. SWD clock
- 10. LED_GPIO. Drives the LED high through 1 kΩ.
- 11. BUTTON_GPIO. Button to GND, 10 kΩ pull-up to 3V3.
- 12. NC. Not connected. Not graded.