This article discusses the criteria for selecting the right microcontroller (MCU) for different embedded applications. It also discusses the design challenges and system limitations of MCUs in embedded applications.
Application in home appliance industry
The home appliance industry uses 8/16/32-bit MCU based circuitry for motor control and TRIAC/LED/LCD drive applications. The MCU controls and manages all functions and features of the home appliances. When you press Start button, inputs go to the MCU from the front-panel keyboard and the MCU starts the three-phase brushless DC (BLDC) motor or the permanent magnet synchronous (PMSM) motor. Motor speed is varied and controlled as per your input from the front-panel keypad.
The MCU uses either internal or external serial EEPROM (I2C/SPI based) to store old data. It uses a real-time clock for displaying accurate time. Temperature measurement is done using an onboard resistance temperature detector, thermistor or thermocouple based temperature-sensing device.
The MCU uses an external analogue-to-digital converter (ADC) and amplifiers for different analogue inputs from sensors, temperature sensors and battery. It uses external signal conditioning, comparators and gate-driver circuitry for driving and controlling the three-phase BLDC/PMSM motor. The MCU receives remote control inputs through an infrared receiver (at 38kHz input).
The MCU uses external buffer-driver circuitry to drive 7-segment LED/LCD/graphical display. Typically, a 7-segment LED/LCD/graphical display with backlight is used for showing the temperature, battery voltage, speed and error/warning messages. The MCU also interfaces with onboard peripherals like I2C/SPI and external peripherals like UART/USB for communication.
Application in automotive industry
The current automotive industry uses 16- to 32-bit MCU based circuitry for e-bikes. The circuitry controls and manages all functions and features of the automobiles. Once you use the ignition key to start the automobile, inputs go to the MCU. This starts the three-phase brushless automotive motor. The MCU receives vehicle input signal and the vehicle starts moving. The MCU uses driver circuitry to drive the three-phase brushless automotive motor as per speed required by the user. Speed of the motor varies and is controlled as per acceleration brake sensor input from the user.
The MCU uses either internal or external serial EEPROM (I2C/SPI based) for storing data like distance readings. It uses RTC for displaying accurate time on the display. Temperature measurement is done by using an onboard RTD or thermistor based temperature-sensing device.
The e-bike solution in the automotive industry uses an obstacle sensor to get information about nearby vehicles while parking, a fuel sensor to get information regarding the amount of fuel in the tank, while an MCU monitors battery voltage and shows it on the LCD display. The MCU uses relay-driver circuitry for switching brakelight/headlight on or off and for blinking directional lights.
The power supply section uses rechargeable lead-acid/lithium battery as the power source. It also has provision for a battery charger. Battery input is down-converted to DC voltage to power the MCU and other circuitry. Ignition key of the e-bike enables and disables onboard regulators.
The power supply section incorporates protection features for battery, over-current, over-heating and start-up fail, which are controlled by the MCU. It also enables charging of external devices like mobile phones.
Application in mobile phones and tablets
Current mobile phone and tablet designs use 8/16/32-bit MCUs as a co-processor for different functions. The MCU receives signals from analogue sensors (temperature sensors like thermistors, resistance temperature detectors and humidity sensors that receive analogue inputs and provide digital voltage, which is applied to the MCU), 2/3-axis accelerometers (that measure 2/3-axis movements and convert it to digital voltage, which is applied to the MCU) and ambient light sensors (ALSes) interface.
Ambient light sensor enables automatic control of display backlight brightness over a wide range of illumination conditions, from a dark environment to direct sunlight. With ALS input, an MCU or baseband processor increases or decreases display brightness, depending on the environment. The MCU also receives magnetic sensor inputs through external ADCs and buffer circuitry. Besides, it uses the accelerometer and mechanical joystick for running gaming applications.