Single channel ADC reading in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an ADC in embedded systems?

ADC stands for Analog-to-Digital Converter. It changes an analog voltage (like a sensor signal) into a digital number the microcontroller can understand.

beginner

Why do we use a single channel ADC reading?

We use single channel ADC reading to measure one analog input at a time, like reading the voltage from one sensor or a potentiometer.

beginner

What is the general process to read a value from a single channel ADC?

1. Select the ADC channel.
2. Start the ADC conversion.
3. Wait for conversion to finish.
4. Read the digital value from ADC data register.

intermediate

In embedded C, which register usually holds the ADC result?

The ADC result is typically stored in a register like ADC Data Register (e.g., ADC_DR or ADC_DATA). This depends on the microcontroller.

beginner

What does polling mean in the context of ADC reading?

Polling means the program waits and checks repeatedly if the ADC conversion is done before reading the result.

What is the first step in reading a single channel ADC value?

A Select the ADC channel

B Start the ADC conversion

C Read the ADC data register

D Wait for conversion to finish

You must first select which ADC channel to read before starting conversion.

What does ADC stand for?

A Advanced Digital Circuit

B Analog-to-Digital Converter

C Analog Data Channel

D Automatic Data Controller

ADC means Analog-to-Digital Converter, which converts analog signals to digital numbers.

How does polling work in ADC reading?

A Program skips waiting and reads immediately

B ADC automatically sends data without waiting

C Program waits and checks if conversion is done

D ADC converts multiple channels at once

Polling means the program waits and checks repeatedly until ADC conversion finishes.

Which of these is NOT part of single channel ADC reading?

A Selecting the channel

B Starting conversion

C Reading the conversion result

D Reading multiple channels simultaneously

Single channel ADC reading reads one channel at a time, not multiple simultaneously.

Where is the ADC conversion result stored?

A ADC data register

B General purpose register

C Program counter

D Stack pointer

The ADC result is stored in a special ADC data register.

Explain the steps to read a single channel ADC value in embedded C.

Think about what you do first, then how you know when to read the value.

Why is polling used in single channel ADC reading and how does it work?

Polling is like waiting for a green light before crossing.

Practice

1. What does a single channel ADC do in embedded C programming?

easy

A. It reads one analog input and converts it to a digital number.

B. It writes digital data to an analog output.

C. It reads multiple analog inputs simultaneously.

D. It converts digital signals to analog signals.

Solution

1. Step 1: Understand ADC function

   An ADC (Analog to Digital Converter) converts analog signals to digital numbers.

2. Step 2: Identify single channel meaning

   Single channel means it reads only one analog input at a time.

3. Final Answer:

   It reads one analog input and converts it to a digital number. -> Option A

4. Quick Check:

   Single channel ADC = One analog input read [OK]

Hint: Single channel ADC reads one input only [OK]

Common Mistakes:

• Confusing ADC with DAC
• Thinking ADC reads multiple inputs at once
• Mixing analog output with input reading

2. Which of the following is the correct way to start an ADC conversion in embedded C?

easy

A. ADC_Stop();

B. ADC_StartConversion();

C. ADC_Read();

D. ADC_Init();

Solution

1. Step 1: Identify function to start ADC

   Starting ADC conversion usually requires a function like ADC_StartConversion().

2. Step 2: Differentiate other functions

   ADC_Read() reads the value, ADC_Init() initializes hardware, ADC_Stop() stops ADC.

3. Final Answer:

   ADC_StartConversion(); -> Option B

4. Quick Check:

   Start ADC = ADC_StartConversion() [OK]

Hint: Start ADC with ADC_StartConversion() [OK]

Common Mistakes:

• Using ADC_Read() to start conversion
• Confusing initialization with start
• Calling ADC_Stop() instead of start

3. What will be the output of this code snippet if the ADC reads a value of 512?

int adcValue = ADC_Read();
printf("ADC Value: %d\n", adcValue);

medium

A. ADC Value: 0

B. ADC Value: 1023

C. ADC Value: 512

D. ADC Value: -512

Solution

1. Step 1: Understand ADC_Read() output

   ADC_Read() returns the current digital value from ADC, here given as 512.

2. Step 2: Print the value

   printf prints the integer value stored in adcValue, which is 512.

3. Final Answer:

   ADC Value: 512 -> Option C

4. Quick Check:

   ADC_Read() = 512 printed as is [OK]

Hint: ADC_Read() returns current ADC number [OK]

Common Mistakes:

• Assuming ADC_Read() returns max value always
• Confusing negative values in ADC reading
• Printing wrong variable or format

4. Identify the error in this ADC reading code:

ADC_Init();
int value = ADC_Read();
ADC_StartConversion();
printf("Value: %d", value);

medium

A. Variable 'value' should be float

B. ADC_Init() is missing

C. printf format specifier is wrong

D. ADC_StartConversion() should be called before ADC_Read()

Solution

1. Step 1: Check ADC function order

   ADC_StartConversion() must be called before ADC_Read() to start conversion.

2. Step 2: Analyze code sequence

   Here, ADC_Read() is called before starting conversion, so it reads old or invalid data.

3. Final Answer:

   ADC_StartConversion() should be called before ADC_Read() -> Option D

4. Quick Check:

   Start conversion before reading ADC [OK]

Hint: Start ADC conversion before reading value [OK]

Common Mistakes:

• Reading ADC before starting conversion
• Ignoring initialization step
• Wrong printf format for int

5. You want to read an analog sensor value using a single channel ADC and convert it to voltage (0-5V) with 10-bit resolution. Which code snippet correctly calculates the voltage?

int adcValue = ADC_Read();
float voltage = ?;

hard

A. voltage = (adcValue / 1023.0) * 5.0;

B. voltage = (adcValue * 5) / 1023;

C. voltage = adcValue * 5.0 / 1024.0;

D. voltage = (adcValue / 1024) * 5;

Solution

1. Step 1: Understand ADC resolution and voltage range

   10-bit ADC means values from 0 to 1023 represent 0 to 5 volts.

2. Step 2: Calculate voltage correctly

   Voltage = (adcValue / 1023.0) * 5.0; uses floating division and full scale 1023.

3. Final Answer:

   voltage = (adcValue / 1023.0) * 5.0; -> Option A

4. Quick Check:

   Voltage = ADC value / max * 5V [OK]

Hint: Divide by 1023.0 for 10-bit ADC voltage calc [OK]

Common Mistakes:

• Dividing by 1024 instead of 1023
• Using integer division instead of float
• Multiplying before dividing causing wrong result