32 DAC and PWM: Output Foundations

32.1 Start With the Decision

This section: Start With the Decision — A digital pin cannot make every analog voltage on its own.

A digital pin cannot make every analog voltage on its own. A DAC turns a digital code into a voltage. PWM switches a pin on and off; its duty cycle is the share of time spent on. Choose the DAC code or PWM duty cycle that the load, the device using the output, can accept.

32.2 Route Overview

This section: Route Overview — This is part 1 of 3.

This is part 1 of 3. Continue with DAC and PWM: Loads, Filters, and Code.

32.3 Learning Objectives

This section: Learning Objectives — Inspect the story panel and ask which output method fits the physical load rather than the software command alone.

• Compute DAC resolution and quantization error.
• Compare true DAC output with PWM duty-cycle output.

Inspect the story panel and ask which output method fits the physical load rather than the software command alone.

32.4 Start Simple

This section: Start Simple — The panel leaves the two output paths unresolved.

The panel leaves the two output paths unresolved. The lamp, reference dial, and actuator do not all respond to the same electrical property: one may tolerate switched average power, another needs a stable voltage, and another brings current, inertia, and timing constraints. The two open paths therefore cannot be labelled DAC or PWM until the load’s ripple, delay, drive, and safety limits are known. This visual introduces the chapter’s comparison without declaring a universal winner. It asks the learner to trace a numeric command into voltage, current, and physical response, then choose the conversion method whose measured output satisfies that particular job. Trace One Number Into a Real Output

Picture a plant lamp that should grow brighter as a control value rises. The computer holds a number, but the lamp needs voltage, current, and safe timing. The path between them decides whether the physical result matches the command.

An analog-to-digital converter means a circuit that turns a voltage into a number; it is called an ADC. A digital-to-analog converter (DAC) means a circuit that turns a number into a voltage or current. Pulse-width modulation means control made by changing how long a signal stays on; it is called PWM. A duty cycle means the share of each cycle spent on. Modulation means changing a signal to carry or control information. An actuator means a part that creates a physical action.

Command minimum, middle, and maximum output. Then lower the supply, change the load, restart the controller, and hold the command at a limit. Measure the real output and keep the actuator in a safe range.

This runway does not size a driver or prove smooth motion. The deeper sections compare conversion, timing, filtering, loads, and the evidence needed to choose an output method.

Imagine a device that must dim a light, set a reference voltage, or drive a small actuator. A DAC produces a stepped analog voltage directly, while PWM makes a fast digital pulse train that a load or filter averages. Start with what the load actually responds to: voltage level, average power, ripple, timing, and acceptable noise.

Math Bridge · guided foundationsWhen does a switching waveform behave like an analogue voltage?Let Eddie connect DAC codes, PWM duty, RC smoothing, ripple, and settling. Learn the maths

32.6 Learning Objectives

This section: Learning Objectives

• Explain DAC Operation: Describe how digital-to-analog converters translate binary values into proportional voltages
• Apply DAC Formulas: Calculate output voltage from digital input using the DAC transfer equation
• Implement PWM Output: Generate pulse width modulation signals as pseudo-analog output for actuator control
• Design RC Filters: Compute component values for low-pass filters that convert PWM to smooth analog voltage
• Interface Actuators: Wire motors, LEDs, and other analog loads to DAC and PWM outputs
• Evaluate DAC vs PWM Tradeoffs: Select the appropriate output method based on application requirements and constraints

32.7 Prerequisites

This section: Prerequisites

Before diving into this chapter, you should be familiar with:

• ADC Fundamentals: Understanding ADC operation helps understand DAC as the inverse process
• Binary Fundamentals: Binary number systems and resolution
• Electricity Fundamentals: Understanding voltage, current, and basic circuits

32.8 Learning Objectives and Motivation

This section: Learning Objectives and Motivation — Follow these connections in order: Reading sensors is only half of an IoT system.

Follow these connections in order: Reading sensors is only half of an IoT system. Devices also need to create outputs: dim lights, drive motors, generate analog control voltages, and shape behavior in the physical world. In real hardware, this chapter explains why PWM is used so often, when a true DAC is worth the extra complexity, and what tradeoff you make when you smooth pulses into an analog-like signal. A beginner who understands this chapter can move from passive sensing projects to systems that actually control something.

32.9 How To Use This Chapter

This section: How To Use This Chapter

• Read the DAC basics first so you understand the ideal case, then read PWM as the practical microcontroller shortcut.
• Tie each concept to a real job: LED dimming, fan speed control, audio output, or voltage reference generation.
• If the filtering discussion feels abstract, imagine what the load experiences: a motor averages pulses differently from a speaker or measurement input.

32.10 Digital-to-Analog Converters (DAC)

This section: Digital-to-Analog Converters (DAC) — Start with the clean case: a digital code becomes a proportional voltage.

Start with the clean case: a digital code becomes a proportional voltage.

DAC = Device that converts digital numbers into analog voltage

Inspect Figure 32.1 with Digital N-bit and code k in mind. Look at how it presents dAC conversion contract from bounded digital code through reference and transfer function to measured analog output before applying digital-to-analog converters (dac).

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Read DAC conversion: code, reference, and load first in Figure 32.1, locate Digital N-bit next, and use code k to interpret their connection. The drawing communicates dAC conversion contract from bounded digital code through reference and transfer function to measured analog output. For digital-to-analog converters (dac), these labels identify the boundary where an assumption must become a calculation or measurement.

32.11 DAC Circuit Architecture

This section: DAC Circuit Architecture — Inspect Figure 32.2 and ask how many distinct output levels a four-bit code can select from a 5 V reference.

Inspect Figure 32.2 and ask how many distinct output levels a four-bit code can select from a 5 V reference.

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Read Figure 32.2 from the four-bit input through the converter and reference to the stepped output. Four bits encode $2^4=16$ possible codes, spanning 0000 through 1111. With the illustrated 5 V reference, dividing the reference range by the code count gives $5\ \text{V}/16=0.3125\ \text{V}$ per step, or 312.5 mV. Each code therefore selects one discrete output level rather than an arbitrary continuous voltage. This is the architectural boundary the chapter uses to compare a DAC with PWM: a DAC directly presents a code-dependent level, while filtered PWM synthesizes an average and brings ripple, load, and settling-time questions.

R-2R Ladder Network:

• Uses only two resistor values (R and 2R)
• Each bit contributes proportional current
• Binary-weighted output voltage
• Low cost, moderate accuracy

32.12 Quantization Error in DAC

This section: Quantization Error in DAC

Quantization appears because an N-bit DAC can produce only one of $2^N$ code levels. Compare the requested smooth waveform with the nearest supported code, and use the step size to bound the ideal amplitude error. Increasing bit depth reduces that vertical step; increasing update rate reduces the time between code changes but does not create new voltage levels. A low-pass filter can attenuate step edges and PWM carrier energy, yet it also changes bandwidth, settling time, and load response. The design therefore selects resolution, update timing, and filtering together, then measures the actual output into the intended load rather than claiming that any one remedy makes the signal perfectly analogue.

Problem: DAC output is not truly analog - it’s discrete steps

Quantization Error = Difference between ideal smooth output and actual stepped output

Reducing Error:

1. Increase bit depth (8-bit → 12-bit → 16-bit)
2. Increase update rate (faster DAC updates)
3. Add filtering (low-pass filter smooths steps)

32.13 True DAC vs PWM Comparison

This section: True DAC vs PWM Comparison — Now move from the ideal component to the practical choice: smooth DAC channel, or PWM plus averaging.

Now move from the ideal component to the practical choice: smooth DAC channel, or PWM plus averaging.

32.14 Continue to the Next Part

This section: Continue to the Next Part — Carry this evidence into DAC and PWM: Loads, Filters, and Code, which begins with PWM, DAC, and RC Simulator.

Carry this evidence into DAC and PWM: Loads, Filters, and Code, which begins with PWM, DAC, and RC Simulator.