Multi-channel ADC scanning in Embedded C - Step-by-Step Execution

Concept Flow - Multi-channel ADC scanning

Start ADC Scan

↓

Select Channel 0

↓

Start Conversion

↓

Wait for Conversion Complete

↓

Read ADC Value

↓

Store Value

↓

More Channels?

Yes→Select Next Channel

No +---> Back to Start Conversion↓

End Scan

↩No +---> Back to Start Conversion

The ADC scan starts by selecting each channel one by one, converting, reading the value, storing it, and moving to the next channel until all are done.

Execution Sample

Embedded C

for (int ch = 0; ch < 3; ch++) {
    ADC_SelectChannel(ch);
    ADC_StartConversion();
    while (!ADC_ConversionComplete());
    values[ch] = ADC_ReadValue();
}

This code scans 3 ADC channels, reads their values one by one, and stores them in an array.

Execution Table

Iteration	Channel Selected	Conversion Started	Conversion Complete?	Value Read	Stored Value
1	0	Yes	Yes	512	values[0] = 512
2	1	Yes	Yes	678	values[1] = 678
3	2	Yes	Yes	345	values[2] = 345
4	-	-	-	-	Loop ends, all channels scanned

💡 Loop ends after channel 2, condition ch < 3 becomes false

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
ch	0	1	2	3	3
values[0]	undefined	512	512	512	512
values[1]	undefined	undefined	678	678	678
values[2]	undefined	undefined	undefined	345	345

Key Moments - 3 Insights

Why do we wait for conversion to complete before reading the value?

Because ADC conversion takes time, reading before completion gives wrong data. See execution_table rows where 'Conversion Complete?' is 'Yes' before reading.

Why does the loop stop after channel 2 and not continue?

The loop condition is ch < 3, so when ch becomes 3, it stops. See variable_tracker where ch final is 3 and exit_note in execution_table.

Why do we store the value in an array indexed by channel?

To keep each channel's reading separate and accessible later. See execution_table 'Stored Value' column showing values stored per channel.

Visual Quiz - 3 Questions

Look at the execution_table, what is the stored value for channel 1 at iteration 2?

A 512

B 345

C 678

D undefined

💡 Hint

Check the 'Stored Value' column at iteration 2 in execution_table

At which iteration does the variable 'ch' become 3?

A After iteration 3

B After iteration 2

C After iteration 1

D Never

💡 Hint

Look at variable_tracker row for 'ch' and see when it reaches 3

If we change the loop to ch < 4, how many iterations will the execution_table show?

A 3

B 4

C 5

D 2

💡 Hint

The loop runs while ch is less than the limit, so increasing limit to 4 adds one more iteration

Concept Snapshot

Multi-channel ADC scanning:
- Loop through each ADC channel
- Select channel, start conversion
- Wait until conversion done
- Read and store value
- Repeat for all channels
- Stops when all channels scanned

Full Transcript

This example shows how to scan multiple ADC channels one by one. The program loops over channels 0 to 2. For each channel, it selects the channel, starts the ADC conversion, waits until the conversion is complete, reads the ADC value, and stores it in an array. The loop stops after scanning all channels. Variables like 'ch' track the current channel, and 'values' array stores the readings. Waiting for conversion completion is important to get correct data. The execution table shows each step clearly, and the variable tracker shows how variables change after each iteration.