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

October/November 2017 | Unmanned Systems Technology 70 Focus | Engine control units system, and a parallel interface for communicating with the MCU. The low-side drivers are there to control a fuel injector, a lamp or LED and a relay or some other load. The pre-driver is intended to drive either an IGBT chip or a bipolar Darlington transistor to control an ignition coil. Generally, the alternative to a pre- driver is an integrated driver as these are smaller, but pre-drivers use external rather than integrated FETs and can therefore handle higher currents and exhibit better thermal performance. The watchdog circuit is a common feature of embedded computers, and it is there to check the performance of the MCU, specifically to guard against software ‘freezes’. The watchdog will restart the MCU if the software fails to reset an independent timer-based decrementing counter before it reaches zero from some predetermined starting number. The presumption is that if the MCU software does not reset the counter it is because it has frozen or hung. The counter’s starting number is chosen to give the watchdog time to restart the MCU in time to execute the next scheduled command. DIY for control While packaged drivers like this are readily available, easy to integrate and relatively inexpensive because of the economies of scale associated with automotive production, some manufacturers prefer to build their own driver circuits for the greater configuration control and security of supply they allow. One ECU developer tells us it tries to stay away from those packaged products because they come and go all the time according to the whims of the manufacturer. Although that means the in-house design ends up with a higher number of small parts on the board, those parts are available from a range of different manufacturers. Non-packaged units, however, tend to have a higher failure rate because fewer of them are manufactured and tested compared with standard packaged devices, and they also tend to take up more space. While there is clearly much scope for variation in the driver and sensor circuitry in an ECU, there is enough similarity between engines to allow ECUs to be adaptable enough to run a wide range of them, although always with some degree of customisation for each application. Further, the same ECU may meet the requirements for a range of different engine management system architectures, regulatory requirements, aircraft integration, interfaces and missions. It would rarely however produce an optimal solution for any individual application, because of factors including weight and volume restrictions, and hardware and software architectures. While the automotive industry has the scale and resources to drive While the electronic components are tiny, ECU volume is often dominated by its I/O (Courtesy of Currawong Engineering) Multifunction packaged power integrated circuits such as this can contain both injector driver and ignition driver circuitry (Courtesy of NXP)