Component values and references in PCB Design - Cell-by-Cell Formula Trace

Sample Data

This table lists PCB components with their reference designators and their electrical values.

Cell	Value
A1	Ref
B1	Value
A2	R1
B2	10k
A3	R2
B3	4.7k
A4	C1
B4	100nF
A5	C2
B5	10uF

Formula Trace

=CONCATENATE(A2, " = ", B2)

Step 1: A2

Step 2: B2

Step 3: CONCATENATE("R1", " = ", "10k")

Cell Reference Map

   A     B
1 Ref   Value
2 R1 -> 10k
3 R2    4.7k
4 C1    100nF
5 C2    10uF

The formula uses cells A2 and B2 to combine the component reference and its value.

Result

   A       B        C
1 Ref     Value    Description
2 R1      10k      R1 = 10k
3 R2      4.7k
4 C1      100nF
5 C2      10uF

The result in cell C2 shows the combined text 'R1 = 10k' describing the component reference and its value.

Sheet Trace Quiz - 3 Questions

What value does cell A2 contain?

A R1

B 10k

C C1

D 100nF

Key Result

CONCATENATE combines component reference and value into a descriptive string.

Practice

1.

What does a component reference on a PCB typically represent?

For example, R1 or C2.

easy

A. The electrical value of the component

B. The size of the component

C. The manufacturer of the component

D. A unique label identifying the component's position

Solution

1. Step 1: Understand component reference purpose

   Component references like R1 or C2 uniquely identify each part on the PCB for assembly and troubleshooting.

2. Step 2: Differentiate from component value

   Component values describe electrical properties (like resistance), not the label.

3. Final Answer:

   A unique label identifying the component's position -> Option D

4. Quick Check:

   Reference = Unique label [OK]

Hint: References label parts uniquely, not their values [OK]

Common Mistakes:

• Confusing reference with component value
• Thinking reference shows size or manufacturer
• Assuming reference is a measurement

2.

Which of the following is the correct way to write a resistor reference on a PCB schematic?

?

easy

A. R10

B. Res10

C. RX10

D. R-10

Solution

1. Step 1: Recall standard reference format

   Resistor references start with 'R' followed by a number, e.g., R10.

2. Step 2: Identify incorrect formats

   Options like 'Res10', 'RX10', or 'R-10' are not standard and may cause confusion.

3. Final Answer:

   R10 -> Option A

4. Quick Check:

   Resistor reference = R + number [OK]

Hint: Resistor references start with 'R' plus number [OK]

Common Mistakes:

• Adding extra letters after 'R'
• Using dashes or special characters
• Using non-standard prefixes

3.

Given the following component list on a PCB:

R1 = 10kΩ
C1 = 100nF
R2 = 1kΩ
C2 = 10nF

What is the total resistance if R1 and R2 are connected in series?

medium

A. 11kΩ

B. 9kΩ

C. 10kΩ

D. 1kΩ

Solution

1. Step 1: Identify resistors and their values

   R1 is 10kΩ and R2 is 1kΩ.

2. Step 2: Calculate series resistance

   In series, resistances add: 10kΩ + 1kΩ = 11kΩ.

3. Final Answer:

   11kΩ -> Option A

4. Quick Check:

   Series resistance = sum = 11kΩ [OK]

Hint: Add resistances directly in series [OK]

Common Mistakes:

• Multiplying resistances instead of adding
• Confusing series with parallel formulas
• Ignoring units (kΩ vs Ω)

4.

In a PCB design file, the component reference R1 is accidentally duplicated for two different resistors. What is the likely problem?

medium

A. The PCB will ignore one resistor

B. The PCB assembly may place wrong parts or cause confusion

C. The resistor values will automatically merge

D. The reference duplication has no effect

Solution

1. Step 1: Understand reference uniqueness

   Each component reference must be unique to avoid confusion during assembly.

2. Step 2: Identify consequences of duplication

   Duplicated references can cause wrong parts to be placed or errors in documentation.

3. Final Answer:

   The PCB assembly may place wrong parts or cause confusion -> Option B

4. Quick Check:

   Unique references prevent assembly errors [OK]

Hint: Each reference must be unique to avoid errors [OK]

Common Mistakes:

• Assuming values merge automatically
• Thinking duplication is harmless
• Believing PCB ignores duplicates silently

5.

You have a PCB with components labeled R1, R2, and C1. You want to create a dictionary in Python mapping references to their values:

{'R1': '10kΩ', 'R2': '1kΩ', 'C1': '100nF'}

Which code snippet correctly creates this dictionary using dictionary comprehension from two lists refs = ['R1', 'R2', 'C1'] and vals = ['10kΩ', '1kΩ', '100nF']?

hard

A. dict_comp = {refs[i], vals[i] for i in range(len(refs))}

B. dict_comp = {refs: vals for i in range(len(refs))}

C. dict_comp = {refs[i]: vals[i] for i in range(len(refs))}

D. dict_comp = dict(zip(vals, refs))

Solution

1. Step 1: Understand dictionary comprehension syntax

   Dictionary comprehension uses {key: value for ...} format, matching keys and values by index.

2. Step 2: Analyze options

   dict_comp = {refs[i]: vals[i] for i in range(len(refs))} correctly pairs refs[i] with vals[i]. dict_comp = {refs: vals for i in range(len(refs))} uses wrong syntax. dict_comp = {refs[i], vals[i] for i in range(len(refs))} uses comma instead of colon. dict_comp = dict(zip(vals, refs)) reverses keys and values.

3. Final Answer:

   dict_comp = {refs[i]: vals[i] for i in range(len(refs))} -> Option C

4. Quick Check:

   Correct dict comprehension syntax [OK]

Hint: Use {refs[i]: vals[i] for i in range(len(refs))} [OK]

Common Mistakes:

• Using comma instead of colon in comprehension
• Swapping keys and values in zip
• Incorrect comprehension syntax