Interfacing PIC Microcontrollers 18. Explore in detail microcontroller interfacing techniques using the popular PIC 16F877 Work through step-by-step examples interactively using circuit simulation software, supplied as assembly source code Gain the knowledge of a wide range of peripheral devices such as keyboards, displays, sensors and drives and serial communication with other processors, memory and more Use interactive simulation software to design and test circuits. | Interfacing PIC Microcontrollers On the other hand it is convenient in microprocessor systems to use the same single supply used by the digital circuits 5 V and to avoid the need to provide separate dual op-amp supplies. Some op-amps are designed specifically to operate with a single supply such as the LM324 type used in the examples here. However 5 V provides only a limited voltage swing the lowest output may not reach 0 V and the maximum will typically be even more limited possibly less than 4 V depending on the op-amp type. The output does not usually reach the supply values due to residual volt drops across internal components. The 324 for example can only reach about V so circuits have to operate within this limited output swing. The 8-bit range in the demo circuits is limited to V so that the amp outputs are operating comfortably within the upper limit but we cannot assume that voltages near zero will be represented accurately. In the test circuits therefore output swing will be limited and offsets introduced to allow the amplifier to operate within its limits. Non-inverting Amplifier The basic configuration for the non-inverting amp is shown in Figure a . The input is applied to the terminal and feedback and gain controlled by the resistor network Rf and R1. If we assume that the voltage between the terminals is zero rule 2 the voltage at the - terminal must be the same as the voltage at the terminal. We can then write down an equation for the feedback network using Ohm s law applied to each resistor assuming the current flow is from the output through the resistors to ground. This is possible because it is assumed that none of the current is lost at the input terminal as it has infinite input resistance rule 3 . A simple re-arrangement of the equation allows us to predict the output voltage in terms of the resistor values. Vo Rf R1 1 V1 The main advantage of this configuration is that the input impedance is very high in theory infinite . The .
