Oscillating circuits 555 timer oscillator

Provided that the circuit constraints are respected, several useful analog circuits can be designed. In particular, we will focus on amplifying circuits. Such circuits open up the possibility to implement sensor amplifiers, comparators, frequency-selective filters, oscillators, timers, feedback-control systems, etc. Figure 9.12 displays the basic one-transistor amplifier. The load resistor gives... 

Thermocapacitive Fiow Sensor, Fig. 6 Circuit of oscillator 555 timer IC chip coupled with sensing capacitor... 

Frequency-Modulated Output When the sensing capacitor is externally connected to a 555 timer 1C chip to form an oscillation circuit as shown in Fig. 6, the oscDlation frequency can be used to measure the flow velocity [10]. Here, both inputs of trigger and threshold in 555 timer are connected together. The respcaise of the output voltage Uo to the input voltage Vc on the capacitor is illustrated in Fig. 7. 

A diode array consists of a series of photodiode/ capacitor parallel circuits positioned side by side on a silicon chip. Each such circuit is connected via its own solid-state switch controlled by a shift register, to a common output line. The shift register is controlled over a quartz oscillator (timer). The readout cycle, corresponding to the illumination time, falls in the 100 ms range. A schematic diagram of the diode array is given in Figure 7. 

A sensor that is especially interesting and instructive is made from a quartz crystal microbalance, or QCM. This device is based on the piezoelectric characteristics of quartz. When quartz is mechanically deformed, an electrical potential difference develops across its surface. Furthermore, when a voltage is impressed across the faces of a quartz crystal, the crystal deforms., A crystal connected in an appropriate electrical circuit oscillates at a frequency that is characteristic of the mass and shape of the crystal and that is amazingly constant as long as the mass of the crystal is constant. This property of some crystalline materials is called the piezoelectric effect and forms the basis for the QCM. Moreover, the characteristic constant frequency of the quartz crystal is the basis for modern high-precision clocks, time bases, counters, timers, and frequency meters, which in turn have led to many highly accurate and precise analyTical instrumental svsiems. 

Integrated Circuit An integrated circuit (IC) also called a chip or microchip is a semiconductor wafer on which thousands or millions of tiny resistors, capacitors, and transistors are fabricated. An IC can function as an amplifier, oscillator, timer, counter, computer memory, or microprocessor. A particular IC is categorized as eiflier analog or digital depending on its intended application. 

A capacitor stores a smaii amount of electric charge it can be thought of as a small rechargeable battery which can be quickly recharged. In electronics we are not only concerned with the amount of charge stored by the capacitor but in the way the value of the capacitor determines the performance of timers and oscillators by varying the time constant of a simple capacitor-resistor circuit. 

The stirrer was made to reciprocate at 3 to 4 cycles/sec by alternately energizing two solenoid coils of double glass-insulated aluminum wire wrapped around the autoclave body. The timing unit consisted of a multivibrator circuit whose frequency of oscillation and cycle time division could be controlled by varying resistances in the circuit. The timer unit, in turn, controlled the grids of two pairs of thyratrons which furnished power to the solenoids. Stirrer operation was monitored by a tickler coil connected to an oscilloscope. 

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