Summary of DAC Sine Wave Generation using TMS320F28027PT with Proteus Simulation
This project implements a PWM-based DAC on a TMS320F28027PT (PICCOLO) microcontroller to generate a clean sine wave. A 256-point lookup table is used with CPU Timer0 interrupts to update PWM duty cycles; the PWM output is low-pass RC filtered (470 Ω, 0.5 µF) and verified in Proteus VSM. The design supports sine, square, and DC outputs and demonstrates firmware, timer-driven updates, and filtering to produce analog signals without a native DAC.
Parts used in the DAC Sine Wave Generation using TMS320F28027PT with Proteus Simulation:
- TMS320F28027PT microcontroller (PICCOLO family)
- ePWM module (on-chip peripheral)
- CPU Timer0 (on-chip timer)
- RC low-pass filter: 470 Ω resistor
- RC low-pass filter: 0.5 µF capacitor
- 3.3V supply
- Proteus VSM simulation environment
Introduction
This microcontroller project demonstrates how a digital-to-analog converter (DAC) can be implemented using PWM on a PICCOLO series controller.
Using Proteus simulation, the project generates a clean sine wave output by filtering a high-frequency PWM signal.
It is a practical example of embedded systems design, combining firmware, timer interrupts, and external RC filtering.
The project is useful for learners exploring DIY electronics, signal generation, and PWM-based DAC techniques.
It also highlights how microcontrollers without native DACs can still produce accurate analog signals.This project demonstrates DAC sine wave generation using PWM on the TMS320F28027PT microcontroller, using a lookup table, Timer0 interrupts, and RC filtering verified in Proteus simulation.
How the Project Works (Overview)
The system uses the PWM module of the TMS320F28027PT to act as a DAC.
A timer interrupt updates PWM duty cycle values taken from a 256-point sine lookup table.
The PWM output is passed through a low-pass RC filter, which removes the carrier frequency and reconstructs the analog sine wave.
This approach allows precise waveform generation using only digital peripherals.
Block Diagram / Workflow Explanation
CPU Timer0 Interrupt triggers at a fixed rate.
On every interrupt, the firmware selects the next value from a 256-sample sine table.
The value is written to the PWM module as a fractional duty cycle.
The PWM signal appears at the output pin.
An RC low-pass filter removes the high-frequency PWM component.
The final output is a smooth analog sine wave observable in Proteus.
Key Features
PWM-based DAC implementation without external DAC hardware
256-point sine wave lookup table for smooth waveform generation
Timer-driven interrupt system for precise waveform timing
RC low-pass filtering to remove PWM carrier frequency
Supports sine, square, and constant voltage outputs via compile-time selection
Fully simulated and verified using Proteus VSM
Components Used
TMS320F28027PT (PICCOLO family microcontroller)
PWM module (ePWM)
CPU Timer0
RC low-pass filter (470Ω resistor, 0.5µF capacitor)
3.3V supply
Proteus VSM simulation environment
Applications
Function and signal generators
Audio waveform generation experiments
Embedded control systems requiring analog references
Teaching PWM-based DAC concepts
Digital signal processing learning projects
Explanation of Code (High-Level)
The firmware initializes the system clock, GPIO, interrupt controller, and PWM peripherals.
CPU Timer0 is configured to generate periodic interrupts.
Inside the interrupt service routine, waveform data is fetched from a lookup table and written to the PWM-based DAC.
The PWM duty cycle changes rapidly, and after filtering, produces a continuous analog waveform.
Different waveform types (sine, square, constant) can be selected using compile-time macros.
Source Code
/**********************************************************************
* Function: main() *
* Description: main function for PWM/DAC example *
* Device: TMS320F2808, TMS320F2806, TMS320F2801 *
* Author: David M. Alter, Texas Instruments Inc. *
* Function Prototype: void main(void) *
* Useage: N/A *
* Input Parameters: none *
* Return Value: none *
* Notes: none *
* History: *
* 02/07/06 - original (D. Alter) *
*********************************************************************/Proteus Simulation
In the Proteus simulation, the PWM output is routed through an RC low-pass filter.
The filter cutoff frequency removes the 3 MHz PWM carrier, leaving a clean sine waveform.
The analogue analysis graph confirms a smooth sine wave with stable amplitude and frequency.
This validates both the firmware logic and the circuit design.
(FAQs)
Conclusion
This project clearly demonstrates how a PWM-based DAC can generate accurate analog waveforms using a PICCOLO microcontroller.
It is an excellent learning example for embedded systems, Proteus simulation, and digital-to-analog techniques.
The design shows how firmware, timers, and simple hardware work together to solve real-world electronics challenges.
- How is the DAC implemented on the PICCOLO microcontroller?
By using the PWM module as a DAC: Timer0 interrupts update PWM duty cycle values from a 256-point sine lookup table. - Why is a low-pass filter required?
To remove the high-frequency PWM carrier and reconstruct the analog sine wave. - Why are 256 samples used for the sine wave?
They provide a smooth waveform while keeping memory usage low. - Can the waveform frequency be changed?
Yes, by modifying the timer interrupt rate or lookup table stepping. - Does this approach work on other PICCOLO devices?
Yes, it is applicable to similar PICCOLO controllers that have PWM modules. - Why use CPU Timer0 for updates?
CPU Timer0 provides precise and consistent timing for waveform generation. - Can square or DC output be generated?
Yes, the code supports square and constant voltage modes selectable at compile time. - What causes waveform distortion in simulation?
Incorrect RC values or a mismatched PWM frequency can affect output quality.
