Electronics

A filter allows for useful frequencies of electronic signals to pass through while blocking or suppressing noise and unwanted frequencies. Using resistors, capacitors, and inductors filters can be designed. For low frequency filters op-amps instead of inductors are used, in order to avoid bulkiness and difficult production requirements. The later is called the active filter, and prior passive filter. Active filter design process is summarized in the block diagram.

Phase Locked Loop is an important circuit found in various communication devices, and here studied in a set up to synchronize input and local carrier signals for coherent demodulation of AM signals. PLL consists of a phase detector, a loop filter, and a voltage controlled oscillator. The phase detector and loop filter combined produces an error signal which amplitude is linearly related to the phase difference of input and local carrier signals. The voltage-controlled oscillator adjusts appropriately to tune both signals as desired.

Temperature is a physical quantity, which needs to be monitored for various applications. The design was part of a larger project where the data of humidity and temperature was to be recorded using a 68HC11 microprocessor over a week. The temperature sensor need to be within +/- 0.5 °c and function properly within the range of +30°c and -20°c.