Hardware Design
Before computer-based electronic computer-aided design (ECAD) was widely available, circuits would be designed as sketches on paper and a layout produced manually. In the absence of fast and powerful computer simulation methods such as SPICE, this process relied more heavily on the experience of the design engineer to be able to predict the circuit performance from theoretical knowledge and practical experience. Numerous prototypes might be needed to arrive at a working solution.
Since the development of increasingly powerful desktop computers, the design process has been radically improved. The designer still has to come up with the original ideas, but circuits can now be rapidly drawn and tested on screen, and a working design quickly produced. The hardware prototype is much more likely to work first time, or at least require less development time. The time taken from design concept to market is regarded as a major competitive factor, so ECAD is now a vital tool for the electronics engineer, just as computer-aided design (CAD) has become in mechanical engineering.
A circuit schematic can now be created, tested and converted into a PCB layout within a single software package, such as Proteus VSM. Complete libraries of all the most commonly used components and microcontrollers are available, which consist of a mathematical model, on- screen circuit symbol and, in selected cases, a physical component pin-out for each. A set of animated components also allows interactive simulation. A circuit can be drawn on screen, the application program attached to the microcontroller and the program tested by operating the on-screen inputs, such as switches and or a keypad, with the mouse. The outputs are then seen
on simulated displays (LED and LCD), or operate animated output devices, such as relays and motors. Examples can be seen in previous chapters.
A further example is shown in Figure 10.1, which will be converted into a PCB layout. It is an electronic dice board with a push button, seven-segment display and buzzer controlled by a PIC 16F84A. It can be programmed to display a random number between 1 and 6 when the button is pressed.
When a suitable program is assigned to the PIC in the simulation (see below), the circuit becomes interactive on screen. When the switch is operated, the display will operate in the same way as the real device. If the chip is programmed to generate a sound output via the buzzer, the waveform can be displayed on a virtual oscilloscope, and reproduced at the PC audio output. The techniques for developing the firmware (Flash ROM software) have been explained in detail in previous chapters.