In this final part of a three-part series about how to pick electronic parts for your electronic project, we will learn about actuators, a few categories or integrated circuits, and power regulation circuit components. This overview is really just a drop in the ocean of parts at your disposal. Component manufacturers are always inventing something new to complete with each other. This brief overview is only intended to give you an idea of what exists, so that you will be more likely to find what you are looking for. Happy hunting!
Actuators give our gadgets the ability to interact with the outside world. These are the things that robots and autonomous vehicles require to move and do work. They are controlled through the presence of a prescribed voltage or a communication interface.
Electromechanical solenoids convert a voltage into a linear motion through the use of a wire wound around a moveable magnetic armature. They have two states of “open” or “closed” and are actuated by the presence of voltage, which causes the magnet to move away from the resulting electric field. When the voltage is removed, a spring returns the magnetic armature to the starting position. Solenoids are normally used for temporary motions, since they consume power whenever they are in one of the available two states. They can be powered by either DC or AC voltages.
Audio Speakers are solenoids that are connected to paper, plastic or metal cones and placed in an enclosure to move air. This creates pressure changes that result in sound or other types of vibrations.
DC motors utilize the small available voltages of an MCU-powered gadget to create rotation. The relative speed can be controlled with Pulse Width Modulation (PWM) as long as the load on the motor is known. If the load on the motor is unknown, the speed of the motor will not be constant over the PWM range. In that case, an encoder device is used to give the necessary feedback to the MCU in order to adjust the PWM value to give the rotational speed required.
AC motors allow higher speeds and torque than DC motors due to the 120 to 240V voltage available at the wall socket, plus up to 15 or 20A of current. AC motors can be controlled by the MCU via relays that isolate the large AC voltage from the small DC voltage that runs the MCU.
Servo motors allow a measured rotation of an arm around a central axis. Like the DC motor, the servo is controlled via a PWM waveform, but in this case the duty cycle of the PWM waveform is used to control the rotational angle of the servo. The servo maintains its angular position as long as the control PWM waveform is applied. Servos are quick to actuate and are used to control the wheels and rudders on remote-controlled toy cars, airplanes, and boats.
Stepper motors are similar to servos but operate on a different principle. They are generally slower to actuate than servos but can maintain their angular rotation even after the control signal is removed and require no feedback to determine the angular position. If used within the torque loads defined in its specification, a stepper motor can be controlled simply with a number of pulses from the MCU.
Integrated Circuits (ICs)
Integrated circuits (ICs, also known as semiconductors or simply “chips”) are the components in your design that will add logic and programmability to your project. These chips are simply bundled versions of all of the foundational electronic components described above. Therefore, many of these ICs can be built on your PCB from a collection of those same discrete components, but the resulting size of the circuit could be prohibitive due to the number of components needed. For example, the microprocessor in your home computer contains over one billion transistors, as well as on-chip capacitors, inductors, resistors, diodes, and other basic circuit elements.
Logic gates can offer basic logic operations such as AND, OR, NOT, XOR, etc. These components are the basis of all integrated circuits that follow. But they can be helpful to use on the circuit board when you are trying to save pins on the MCU. For example, suppose you have a safety mechanism which requires two buttons to be pushed at the same time for some function in your device to activate, like the self-destruct sequence, or maybe just resetting the gadget to the default state. Rather than use two pins on the MCU, you can combine the two inputs through an AND gate, and then a single GPIO pin on the MCU can be used to detect activity on two buttons at once, but only if they are both being pressed at the same time.
Optoisolators are a combination of a photo diode and photo transistor in the same package. These devices are the simple combinations of exactly two discrete components. They provide electrical isolation of two circuits, using only light as the bridge between electronic circuits.
Digital potentiometers provide adjustable resistance to a circuit via digital interface such as I2C or SPI. They can be ordered according to the absolute resistance range available, number of programmatic steps, and accuracy. This is a way to add a software programmable resistance value to your circuit.
Amplifiers can be formed with a single transistor but can also be in the form of ICs that create operational amplifiers (OpAmps), specialized to power regulation purposes or for high fidelity applications such as audio.
Multiplexers (or Muxes) are components that combine the functions of many logic gates to create an input selection device. The mux will sample its control lines to determine which input pin voltage is connected to the output pin. These devices can be used in an audio mixer to select a single source signal from a set of possible input sources.
Demultiplexers (or Demuxes) perform the opposite function of muxes. The control pins specify which output pin is assigned the voltage present at the input pin. They are normally used at the receiving end of a signal that was previously multiplexed.
Decoders provide a translation from a set of input pins to a set of output pins. This device can translate a number encoded on the inputs into a single output that is the value of the number. For example, a 2-to-4 decoder can accept a two-digit code and assert only one output depending on the value of number represented by the four pins. These can be useful to save pins on the MCU.
Encoders perform the opposite of decoders, allowing many signals to be compressed into a combinatorial that effectively compresses the number of pins needed to read the values of many inputs. Again, these can save pins on the MCU.
GPIO expanders give the designer more GPIOs than what may be available on the MCU. The interface to the MCU is typically I2C or SPI, and can be configured as input or multiple types of outputs such as open-drain, push-pull, etc. These devices can allow full bidirectional, full-time control of each additional GPIO line, unlike muxes, demuxes, encoders and decoders. GPIO expanders might also give the designer special features such as higher current capacity and PWM-capable GPIOs that can all be configured through configuration registers.
Analog-to-Digital Converters (ADC’s) and Digital-to-Analog Converters (DAC’s) are available in the EFM32 family as onboard peripherals, but can also be used as an external IC with an I2C or SPI interface. This allows the designer the ability to pick higher-resolution converters or simply add more ADC’s to the design.
Audio chips are available that can convert digital encoded (PCM) audio into PWM output waveforms through a bus interface called I2S. Some audio devices have onboard amplification for direct connection to a speaker. Sound effects chips contain onboard non-volatile storage, such as ROM or flash memory, that stores sounds onboard for later playback from the MCU and may also record audio from a microphone.
Display chips allow the control of display screens through I2C, SPI or parallel interfaces. The EFM32 family has several interfaces available for controlling some types of displays. Some display chips contain non-volatile storage with built-in handling of resistive and capacitively-coupled touch screen interfaces and can contain coprocessors for rendering images from MCU instructions without burdening the MCU with the pixel-by-pixel computations.
Interface and Communication chips provide a way to connect the MCU to the outside world through standard, widely available interfaces such as Ethernet, UART, USB, RS-232, or even I2C or SPI bus expanders and hubs.
Radio Frequency (Wireless) chips and modules allow your gadget to connect your gadget without wires through standards such as Bluetooth Low Energy (BLE, also known as Bluetooth Smart), ZigBee, WiFi, and mobile networks, as well as to non-standard devices such as garage door openers and radio-controlled toys. Note however that any design sold to end users (not for kit or evaluation purposes) that broadcasts RF energy needs to be licensed by the FCC, which is an expensive process. A pre-licensed module can avoid that process, albeit with higher component cost.
Memory chips add additional volatile and non-volatile memory to your design. Volatile memory, typically Random Access Memory (RAM), will not retain its state after the power is removed and is typically used for a fast holding place for large sets of information. Non-volatile memory, such as flash memory, will retain its state after power is removed, but can be slower to write or read. The EFM32 family of MCU’s is ordered according to the amount of both RAM and flash memory that is built into the MCU.
Programmable Logic Devices (PLD’s) offer custom on-chip logic. This device allows the designer to create custom combinatorial logic circuits right on the chip itself through the use of a programming-like language. This has the benefits of fast execution and offloading the MCU from making timing-critical computations on hardware signals.
Power Regulation ICs
All components in your gadget consume some amount of current at a prescribed voltage range, so it is often required to convert voltages in order to supply the right kind of power for each component. Devices that connect to a wall socket for power can utilize alternating current (AC) power in the 120 volt to 240 volt range that deliver up to 15 amps of current. This is useful for driving powerful motors or heaters, for example. However, any integrated chips (ICs) that are necessary to control the device and give it smarts will require that the AC power is converted to direct current (DC) voltage. This can be accomplished in a single step through the use of an off-the-shelf AC/DC power supply, also known as a “wall wart”, available in a wide range of voltage and current outputs. The most typical AC/DC converters to be used for EFM32 projects is a 3.3V supply, since the EFM32 operates in a range of 2.5V to 3.6V. Once the 3.3V supply is provided to the gadget, all components that require power will have to be chosen such that they can operate on that same voltage. Often, some devices chosen for the design will require a higher or lower voltage. When there is a need for more than one required voltage on a single board, a voltage regulator chip will be required to convert the voltage for those devices.
Any electrical component that operates directly from a battery must be chosen such that the full range of battery power is permissible for the device. For example, a pair of fresh AA batteries create a maximum of 3V but drop down to about 2V when depleted. In addition, any battery will see a drop in voltage when under a heavy current load. All of this must be considered when picking components that can handle the lifetime voltage range. For example, many LEDs have a forward voltage of around 3.2V. When the batteries start to drain and can’t provide the correct forward voltage, the brightness and even the color shade of the LEDs can change unless the battery voltage is further regulated to a standard onboard voltage.
Regulators can be fixed or variable output. The fixed regulators can accept a fixed or variable input voltage but deliver a factory-set output voltage. A variable regulator might accept a fixed or variable input but produce a variable range of output voltage, typically set via configuration resistors. Some advanced regulation chips can utilize programmable interfaces such as I2C or SPI to set the output voltage.
The following types of regulators can help you supply all of your components with the proper voltage. All voltage regulators have a limit to the amount of current that can be delivered, which is part of the component specification.
Linear regulators convert a higher voltage to a lower voltage and waste energy in the form of heat in the process, but can deliver clean power with no added noise. They can be effective if the amount of power delivered is very small and the voltage difference between input and output voltage is small. For example, a component that requires 2.5V and only consumes 5mA of current could very well use a 3.3V to 2.5V linear regulator. The wasted power would be 0.2V x 5mA = 1mW. This could be good for some applications but would be an unacceptable power draw for a device that runs on the tiniest of batteries or energy harvesting. The main reason to use a linear voltage regulator is to keep the output as ripple-free as possible.
Low Dropout (LDO) regulators are linear regulators that are designed to output a voltage that is very close to its input voltage. Normal linear regulators specify a larger delta between the input and output voltage. The “dropout” is the voltage difference between the regulator input voltage and output voltage.
Zener Diodes provide a special-case way to regulate the output voltage linearly by simply capping the amount of voltage that is present at the pins of the diode. It does this by shunting excess current to ground to maintain a required voltage.
Switching regulators utilize digital clocks and output stage filters (inductors and capacitors) to efficiently convert an input voltage to an output voltage. The design improves power efficiency and are more complex and expensive than linear regulators but can create unwanted noise, particularly if the output stage filters are not chosen carefully for high quality. They generally require a large, high-quality inductor to filter the resultant voltage.
Buck regulators (also known as step-down regulators) are a type of switching regulator that requires a higher input voltage than the output voltage.
Boost regulators are a type of switching regulator that requires a lower input voltage than the output voltage.
Buck-Boost regulators are a type of switching regulator that have no constraint of the input voltage versus the output voltage and provide both buck and boost functions in one device.
Charge Pumps are capacitor-based switching regulators that have high efficiency under low current load and are typically low cost, as they do not require an inductor.
This wraps up the chapter on component selection. You should now possess the necessary lingo to at least begin to browse the universe of components available today.