Timer Oscillator

The astable operation of the UA555 as an oscillator has a duty cycle and free running frequency, which are both precisely controlled with two external capacitors and two resistors. The circuit is shown in Fig. 8.1. 

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The circuit was constructed in the laboratory. The values of Rl, R2, Cl, and C2 are the actual measured values of the components used in the circuit. A Tektronix TDS 340A digital real-time oscilloscope was used to record the output data, as shown in Fig. 8.2. The duty cycle was calculated to be 66.7%, and the output voltages oscillated from 5 V to 10 V. The simulated data, from IsSpice, Micro-Cap V, and PSpice, are shown in Figs. 8.3, 8.4, and 8.5, respectively. Table 8.1 illustrates the variances in the simulated output data. 

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In addition, before end items suitable for military application can be developed, the following design limitations must be overcome 1) Oscillator stability, timer accuracy and reliability. under such end item conditions of environment as military temperature range and spin 30000rpm(max for artillery fuzing), 2) Ruggedness, 3) Need for adequate power supply (for up to 200 secs operation),... 

In a typical electronic fuze timer the fundamental components are an oscillator and a binary counter. Lining flueric tech-... 

Digital timers of excellent quality that are based on crystal oscillators are available. The resonant frequency of such oscillators is temperature dependent and subject to aging effects, but the state of the art is highly developed. Crystal-controlled clock oscillators having a maximum error of 1 ppm at 25°C are commercially available from a number of manufacturers. Some units are tem-... 

The main timer types are precision reference, electronic, mechanical, pyrotechnic, flueric and electrochemical. Also covered are fluid timers (not to be confused with flueric timers) and nuclear decay timers. Electronic and flueric timers are similar in that they both use oscillators, amplifiers, and related networks to achieve tuning and frequency control. In mechanical... 

Figure 3. Device for measuring tack-free time (1) probe (absorbent cotton) (2) timer controlling interval between exposure and activation of probe (3) oscillating stage (4) exposure timer (5) constant temperature bath and circulator (6) air pressure regulator controlling pressure on probe (7) General Electric UA-3 mercury arc, reflector, and shutter (inside enclosure)...

An intriguing feature of the cyanobacterial KaLABC circadian clock is that analysis of the structure and function of the central timer requires no concern with input and output. Beyond an understanding of how three proteins are able both to sustain a stable oscillation with a period of 24 h and to do... 

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. 

The accuracy with which elapsed time can be measured is rarely a limitation in modern instruments. The frequency of the AC power lines is of sufficient accuracy in most locations, except for very short times (less than a few cycles). If higher precision is needed, and for battery-operated instruments, a timer based on a crystal-controlled oscillator is capable of precision to better than 1 part per million. Sufficient accuracy for many purposes can conveniently be obtained from the time-base of a strip-chart recorder on which the detector response is plotted. Older instruments depended on a hand-held stopwatch or other mechanical or electromechanical device. 

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