Unmanned Systems Technology 016 | Hydromea Vertex AUV | Power management systems | Unmanned Space Vehicles | Continental CD-155 turbodiesel | Swift 020 UAV | ECUs | DSEI 2017 Show report

69 Drivers and drivers Many of these components are therefore referred to as drivers, which can be a source of confusion to the uninitiated because the term is applied to both the computer software used to control a peripheral device and the electronic hardware in the form of analogue power ICs – and ECUs contain both kinds. A software driver running on the microprocessor communicates with an ASIC that in turn controls a hardware driver that controls a component on the engine, such as a fuel injector, ignition coil, throttle motor, a remote device such as a fuel pump or a comms link. To talk over a CAN bus, for example, there will be a CAN driver – a piece of software – and there will also be a physical transceiver, also called a driver. To drive a fuel injector, the software driver in the microprocessor sends a tiny digital command signal to the ASIC, which then runs its own logic to create the exact waveform that the injector needs. Like the microprocessor, however, the ASIC cannot carry the current required to operate the injector solenoid, so it provides a ‘pilot’ signal for the high-current FET chips that ultimately drive the injector. So while the microprocessor is ultimately in control of all the devices on the engine, it can be anything between two and ten steps removed from them. These steps are different stages of drive circuitry, such as high-side drivers that output a high voltage to turn something on and that can apply pulse width modulation (PWM) to control currents through components. Adjusting the PWM based on sensor feedback allows closed-loop control of fuel pressure, for example. There are many types of analogue electronic driver, and the types and numbers included in an ECU are determined early on by what the engine designer decides to use as actuators and as inputs to the ECU. The ECU also receives signals from sensors around the engine. These sensors measure engine parameters in real time and are critical to closing the loop. The signals these sensors supply are typically in the form of voltages or resistances. Resistor-based sensors are passive and therefore do not transmit signals. Typically the voltage across them is actively read by the ECU, usually by polling the sensor port. Packaged power ICs Many drivers and other specialised devices can be bought as complete analogue power ICs ready to go on a board, sometimes with combined functions. These packaged devices offload some of the pressure and are purposefully designed to perform a specific task. One example designed for single- and twin-cylinder engines is described as a multifunctional ignition and injector driver system. It consists of three integrated low-side drivers, one pre-driver, a voltage pre-regulator that supplies 5 V to the ECU’s embedded microcontroller unit (MCU, the ECU’s ‘brain’), a watchdog circuit for the MCU, an ISO 9141 K-line interface with the diagnostics Engine control units | Focus Most UAV internal combustion engines are single-cylinder units like this, or twins, whose ECUs tend to be simple devices (Courtesy of the US Department of Defense) Unmanned Systems Technology | October/November 2017 An ECU printed circuit board, populated with integrated circuits and discrete electronic components such as transistors (Courtesy of Moscat Ingeneria)