Posts by Farahat

Relay Control The relay was the first control system component to be invented, originally to boost telephone signals. It is an electromechanical switching device, which allows a high power load to be controlled by a small input current, using an electromagnetic coil to operate a set of changeover switches. Relays can be wired up to […]
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Input/Output Allocation The I/O functions provided by the PIC 16F887 are detailed in Table 13.2. These were mapped against the requirements of the application, and the most convenient grouping was decided, giving the I/O allocation in Table 13.3. Circuit Description Figure 13.3 shows the schematic for the temperature controller. Each interface will be described separately. […]
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Control Technologies Microprocessors and microcontrollers are part of a wide range of technologies used in control systems. These include: • Electromechanical relays • Programmable logic controllers • Microcontroller-based boards • Dedicated microprocessor designs • PC-based controllers • Networked control systems. To complete an overview of controllers, and to allow comparison with PIC microcontroller- based systems, […]
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Other Microcontrollers The PIC currently dominates the 8-bit microcontroller market, but a comparison with other controllers is still useful, particularly as the alternatives are generally based on historically significant conventional architectures using complex instruction sets, which provide a useful contrast with the PIC reduced instruction set computing (RISC) architecture. Intel® 8051 Microcontroller The Intel PC […]
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PIC C Programming For those readers unfamiliar with C programming, a simple example is shown in Program 13.3. The program will give the same output as BIN1.ASM assembly language program. The program must be converted to PIC 16-bit machine code using the MPLAB C18 Compiler, which is supplied as an add-on to the development system. […]
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Program SCALE1 This program will output a musical scale of eight tones. The frequencies for a musical scale from middle C upwards are 262, 294, 330, 349, 392, 440, 494 and 523 Hz. These can be translated into a table of delay counts which give the required tone period, since period T ¼ 1/f (s), […]
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Advantages of C Programming The C compiler converts the program into PIC 16-bit machine code. Most of these C statements translate into more than one machine code instruction. This can be confirmed by studying the list file, which is produced by disassembling the machine code. The pseudocode for the temperature controller above (Program 13.2) can […]
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16F818 Temperature Controller The PIC 16F818 is a replacement part for the 16F84A. It has a compatible pin-out (Figure 13.8), and additional features at a lower cost. Sixteen I/O pins are available, including five analogue inputs. It has 1k words of program memory; if extra memory is needed, the 16F819 has the same features but […]
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Motor Application Board MOT2 We will investigate these ideas via a general purpose motor test board design, MOT2, which can control a dc motor requiring up to 30 A drive current. This is provided by a full bridge driver that allows bidirectional speed and position control with pulse feedback (servo motor). MOT2 is based on […]
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12F675 Temperature Controller The 10 and 12 series of PIC mini-chips offer a minimal set of features in eight-pin packages. The pin-out for the 12F675 illustrates the point (Figure 13.10). It can be configured with six plain digital I/O pins, but also offers two timers, an analogue comparator or four analogue input channels. The 12F629 […]
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