Simple ADC - Analog to Digital Converter Example

Overview

This NetBurner application demonstrates basic analog-to-digital conversion on MCF5441X-based platforms. The application continuously reads all 8 ADC channels and displays both raw register values and converted voltage readings on the serial console.

Supported Platforms

MOD5441X - All 8 ADC channels available
NANO54415 - All 8 ADC channels available

‍Note: Refer to your specific platform's datasheet to determine which ADC channels are routed to accessible connector pins.

Hardware Requirements

NetBurner MOD5441X or NANO54415 module
Analog voltage sources (0-3.3V) connected to ADC input pins
Serial console connection for output display

ADC Specifications

Resolution: 15-bit (32,768 counts)
Input Range: 0V to 3.3V
Channels: 8 single-ended inputs (AN0-AN7)
Conversion Type: Successive approximation
Reference Voltage: 3.3V

Application Functionality

Main Features

Single-Ended ADC Configuration: Initializes all 8 channels for single-ended input
Continuous Conversion: Performs ADC conversions every second
Dual Output Format: Displays both raw hex values and calculated voltages
Synchronous Operation: Waits for conversion completion before reading results

Program Flow

Initialization
- Initialize network stack with init()
- Enable system diagnostics
- Initialize ADC hardware with InitSingleEndAD()
Main Loop (repeats every second)
- Start ADC conversion with StartAD()
- Wait for conversion completion using ADDone()
- Read and display all 8 channel results
- Convert raw values to voltage
- Wait 1 second before next cycle

Output Format

The application displays readings in two formats for all 8 channels:

Register values: 0000,0000,4A2B,0000,0000,0000,0000,0000,

Voltage: 0.0000,0.0000,1.5234,0.0000,0.0000,0.0000,0.0000,0.0000,

Register values: Raw 16-bit hexadecimal ADC readings
Voltage: Calculated floating-point voltage values (0.0000 to 3.3000V)

Key Components

Files Structure

SimpleADC/
|-- src/
|   |-- main.cpp      # Main application logic
|   |-- SimpleAD.cpp  # ADC driver implementation
|   +-- SimpleAD.h    # ADC function declarations
|-- makefile          # Build configuration
+-- README.md         # This documentation

Core Functions

**InitSingleEndAD()**: Configures ADC hardware for single-ended operation
**StartAD()**: Initiates conversion on all enabled channels
**ADDone()**: Returns true when current conversion cycle is complete
**GetADResult(int ch)**: Returns raw 16-bit result for specified channel (0-7)

Voltage Conversion Formula

voltage = (raw_value * 3.3) / 32768.0

Where:

raw_value: 16-bit ADC result (0-32767)
3.3: Reference voltage
32768.0: Full-scale count (2^15)

Hardware Connections

ADC Channel Mapping

Consult your platform's datasheet for specific pin assignments:

Channel 0 (AN0): ADC input 0
Channel 1 (AN1): ADC input 1
Channel 2 (AN2): ADC input 2
Channel 3 (AN3): ADC input 3
Channel 4 (AN4): ADC input 4
Channel 5 (AN5): ADC input 5
Channel 6 (AN6): ADC input 6
Channel 7 (AN7): ADC input 7

Input Requirements

Voltage Range: 0V to 3.3V (do not exceed 3.3V)
Input Impedance: High impedance (suitable for most sensors)
Signal Conditioning: May require buffering for low-impedance sources

Usage Examples

Testing with Known Voltages

Ground Reference: Connect ADC input to GND (should read ~0.0000V)
3.3V Reference: Connect ADC input to 3.3V supply (should read ~3.3000V)
Variable Voltage: Use potentiometer or voltage divider for variable input
Sensor Testing: Connect analog sensors (temperature, pressure, etc.)

Monitoring Multiple Channels

Connect different voltage sources to multiple channels to observe simultaneous readings:

Register values: 0000,7FFF,4000,2000,1000,0800,0400,0200,

Voltage: 0.0000,3.3000,1.6500,0.8250,0.4125,0.2063,0.1031,0.0516,

Troubleshooting

Common Issues

All readings show 0000
- Check that ADC inputs are properly connected
- Verify input voltages are within 0-3.3V range
- Ensure proper ground connections
Readings are unstable or noisy
- Add input filtering (RC filter recommended)
- Check for proper ground plane connections
- Verify signal source has adequate drive capability
Incorrect voltage calculations
- Verify reference voltage is exactly 3.3V
- Check ADC resolution settings in code
- Confirm conversion formula matches hardware configuration

Debug Tips

Use multimeter to verify actual input voltages
Connect known reference voltages for calibration
Monitor ADC register values for consistency
Check platform-specific pin assignments in datasheet

Technical Notes

ADC Characteristics

Conversion Time: Platform-dependent (typically microseconds)
Sample Rate: Limited by software delay (1 Hz in this example)
Accuracy: Dependent on reference voltage stability
Temperature Drift: Consult datasheet for specifications

Performance Considerations

Current implementation uses polling for conversion completion
For high-speed applications, consider interrupt-driven conversions
Multiple channel readings are sequential, not simultaneous
Adding input filtering may improve measurement stability

Application Extensions

This basic example can be extended for:

Sensor Integration

Temperature sensors (thermistors, LM35)
Pressure transducers
Light sensors (photodiodes, photoresistors)
Position sensors (potentiometers)

Advanced Features

Averaging multiple readings for noise reduction
Threshold monitoring with alarms
Data logging to file system
Web-based real-time monitoring
Calibration and scaling for specific sensors

Code Modifications

// Example: Add averaging for channel 2
float avgVoltage = 0;
for(int sample = 0; sample < 10; sample++) {
    StartAD();
    while(!ADDone()) asm("nop");
    avgVoltage += ((double)GetADResult(2)) * 3.3 / 32768.0;
    OSTimeDly(TICKS_PER_SECOND / 100); // 10ms between samples
}
avgVoltage /= 10;
printf("Channel 2 averaged voltage: %6.4f\r\n", avgVoltage);

Related Examples

PeriodicADC: Interrupt-driven ADC conversions
DAC Examples: Digital-to-analog output generation
PWM Examples: Pulse width modulation for analog control