ATD Converter and Measurement Devices

Course Information

• Course name: CSE211s Introduction to Embedded Systems
• Semester: Fall 2024
• Topic: Analog Interfacing

Analog Interfacing Overview

• Analog and Digital Signals: Basics of ADC & DAC (ATD & DTA) Conversion
• Analog Interfacing: Signal Conditioning
• Example: STM32F401RE Analog Module (only ADC)

Typical Microcontroller Components

• MCU: Central processing unit
• Digital I/O: LEDs, LCDs, Switches, Relays, Keypads
• Analog I/O: Sensors, Actuators, Limit Switches, Photo Detectors, PWM
• Communication: UART, SPI, i2C, Bluetooth, Wi-Fi, Ethernet
• Other Digital Devices
• Memory: ROM, RAM
• Clocks
• Timers
• The Internet
• Wired/Wireless

Analog Signals and Embedded Systems

• Embedded systems often need to measure physical variables that are typically time-continuous.
• Transducers produce analog values (e.g., voltage) that are unsuitable for digital computers.
• Examples of physical variables include temperature, pressure, light intensity, acceleration, rotary position, and mechanical strain.
  • Temperature: Thermometer, Thermostat, Car Engine Cooler, Chemical Reaction Monitor
  • Pressure: Blood Pressure Monitor, Altimeter, Car Engine Controller, Scuba Dive Computer, Tsunami Detector
  • Light: Digital Camera, IR Remote Control Receiver, Tanning Bed, UV Monitor
  • Rotary Position: Wind Gauge, Knobs
  • Acceleration: Air Bag Controller, Vehicle Stability, Video Game Remote, Mechanical Strain
  • Other: Touch screen controller, ECG, EEG, Breathalyzer

Analog & Digital Signals

• Digital computers allow for sophisticated numerical algorithms (e.g., in automatic control and signal processing) not possible with analog electronics.
• Digital signals are suitable for storage, processing, and communications.

Continuous/Discrete-time & Digital Signals

• Analog signals are defined for all real time (t ∈ ℝ).
• Discrete-time signals are defined only at discrete time instants (t = nT, where n is an integer and T is the sampling time).
• Digital signals are discrete-valued (quantized) and represented by a finite number of digits.

A Digital Control Loop

• A digital controller performs control action through 3 steps:
  1. Sample the system variable using Analog-to-Digital conversion (ATD, ADC, or A/D)
  2. Process the sampled data according to a built-in control algorithm.
  3. Output the control action using Digital-to-Analog conversion (DTA, DAC, or D/A).

ATD/DTA Conversion

• Analog Value: Defines the range and polarity of operation (uni or bipolar)
• Digital Value: Number of bits and levels (2ⁿ).
• Resolution: Ability to differentiate close values. It's (VH - VL) / (2ⁿ - 1) where V_H, V_L are the high & low voltage values respectively and n is the number of bits

ATD Converter

• SC signal triggers the conversion process.
• EOC signal indicates the end of conversion.

DTA Converter

• Write pulse stores the new binary input value.
• Zero-order-hold (ZOн) maintains constant analog output until the next Write pulse.

ATD Conversion Example

• Formula for input voltage calculation: VIN = VL + ((VH - VL)/(2ⁿ-1)) × D, where D is the digital value.

Signal Conditioning Circuit

• Sensor output voltage range might differ from the ATD input range.
• Signal conditioning circuits translate sensor output to a suitable range for the ATD.
• They may also amplify or filter the input signal or convert current/charge to voltage for the ATD.

Signal Conditioning Circuit (Range Translation)

• Signal conditioning formulas often include gain and bias.
• Translation formula: VOUT = VL + ((VH - VL)/(V2 - V1)) × (VIN - V1)
• Amplifier Gain: A = (VH - VL)/(V2 - V1)
• Bias: B = AV1 - VL

Signal Conditioning: Amplification & Bias

• Graphical examples of sensor output and output after amplification and bias are provided.

Inputs to ADC

• Single-Ended: Input voltage referenced to ground.
• Differential: Two inputs, measuring the difference between them; provides good noise immunity.
• Multiplexing: Sharing a single ADC with multiple inputs by selecting inputs sequentially to settle before sampling.
• Signal Conditioning: Amplifiers, filters, and clamping diodes to protect against out-of-range inputs.

Sample and Hold Devices

• Some ATD converters require the input to be held constant during sampling using a "sample and hold" circuit with a switch and capacitor.

MCU Analog Modules Features

• ATD (Analog to Digital): Number of on-chip ADCs, multiplexed input signals, number of analog input pins, range of the analog input signal, resolution, single/differential inputs, interrupt capabilities.
• DTA (Digital to Analog): Number of on-chip DTAs, number of analog output pins, range of the analog output signal, resolution, interrupt capabilities

STM32F401RE Analog Module

• The STM32F401RE has one ADC, but no DAC.
• Different features and modes of operation for the ADC are described (Features, Initialization & Configuration, Operation, Example application)

Reset State

• Peripherals are disabled after reset.
• Alternate functions are inactive.
• I/O ports are in an input floating mode.

STM32F401RE ADC Features

• Resolution: Configurable (12-bit, 10-bit, 8-bit, or 6-bit)
• Range: VREF- ≤ VIN ≤ VREF+ (1.8 V ≤ VREF+ ≤ VDDA), where VREF is the reference voltage, VSSA.
• Input Channels: Up to 16 external analog input channels with internal temperature and voltage sources.
• Sampling Time: Programmably set.
• Trigger Sources: By Software, Hardware / Timer, External (EXTI line)
• Digital Result: Stored in a register.
• Interrupt Capability
• Conversion Modes: Single-shot, continuous, scan.
• DMA capability

Modes of Conversion

• Single: One conversion at a time
• Continuous: Continuous conversion mode starts a new conversion as soon as the previous one is finished
• Scan: scans through channels automatically

Initialization & Configuration

• Detailed steps for ADC initialization and configuration for a single channel, including enabling the ADC, setting up GPIO pins, selecting conversion mode, input channel, and trigger source (Software or Hardware)

Configuration

• The ADC samples the input voltage for a programmable number of ADCCLK cycles (using the SMP[2:0] bits in registers ADC_SMPRI and ADC_SMPR2). Conversion time is determined by the sampling time and 12 clock cycles.
• Options for triggering the conversion (software, timer, external trigger signals) are described.

Operation

• Describes how the ADC operates based on the configuration (software trigger or hardware trigger)
• The conversion of the selected channel is complete, data is stored into the 16-bit data register ADC_DR (right and left alignment), the end of conversion flag is asserted

Mbed Analog Input Example

• Code example of using analog input to turn on an LED if the input exceeds a threshold.

Mbed Analog Output Example

• Code example of generating a 10-step ramp output using analog output on a pin.

Appendix

• Supporting documents, tables (e.g. register settings) are included.

This quiz covers the functioning and components of the ATD converter process, including key terms and operations involved in analog-to-digital conversion. It also explores various measurement devices like thermometers, altimeters, and blood pressure monitors, highlighting their significance in different applications. Test your knowledge on these important concepts in electronics and measurement.