Rongge

The oscillator shown in Figure1 is frequently used in digital circuits and may, therefore, look very familiar. Many readers may not know that this type of oscillator suffers from a nasty draw-back caused by noise. When the amplitude of the noise is higher than the hysteresis of the gates used for the oscillator, spurious switching pulses are generated near the zero crossings. This problem can be cured only by ensuring that the rise time of the input signal is shorter than the reaction time of the relevant gate. When the oscillator is built with fast logic gates, such as those in the HC-series, the like-lihood of the problem occurring is great. However, as long as the positive feedback is fast enough, nothing untoward will happen. However, when delays occur owing to the transit time of the components used, the problem may rear its head. In the configuration of Figure 1a , the signal passes through two inverters and thus experiences twice the transit time of a single gate. The upper sig...

This basic circuit is simple to create and the tool's are not critical . Most of them can be found in your junk parts box . The L1 antenna coil can be made by close winding 8 to 10 turns of 22 gauge insulated hookup wire around a 1/4 inch form such as a pencil . You can exeprement with the size of the copile and the number of  turns to see how it affects the frequency and singnal out put of the oscilatter . You ought be able to pick up its signal with a standard FM radio receiver . The signal in ought be coupled by a disc capacitor of about 0.1 uF to stage in main of it . Author            Saifullah soomro

Crystal oscillators for digital circuits are normally built as Pierce oscillators with an inverter.The inverter operates as a linear amplifier and thus requires extra current. But you can also build a crystal oscillator using an  operational amplifier (op amp for short)! If a  very low frequency is involved, for instance  32.768 kHz (commonly used for clocks), you can get away with a comparatively ‘slow’ micro power op amp. Circuit diagram : Micropower Crystal Oscillator Circuit Diagram In the sample circuit shown a widely avail-able TLC271 is used. On pin 8 we have the  opportunity to set the ‘bias mode’, with three  choices ranging between fast operation with  higher current consumption and slower operation at low current. For our clock crystal the middle setting will suit us fine. Pin 8 is there-fore connected to the voltage divider R1/R2. The current consumption of the entire circuit  is impressively modest and at 5 V this is just  56 µA! The oscillator also functions astoundi...

This is the Simple Overtone oscillator with crystal switching Circuit Diagram. The large inductive phase shift of LI is compensated for by Cl Overtone crystals have very narrow bandwidth;, the re fore, the trimmer has a smaller effect than for fundamental-mode operation.  Simple Overtone oscillator with crystal switching Circuit Diagram

Most engineers will recognise the problem: Your circuit needs a stable 1 or 2 MHz clock generator (in the author’s case it was for a Pong game using an old AY3-8500). A suitable crystal is not to hand so you cobble together an RC oscillator (there are plenty of circuits for such a design). Now it turns out that you don’t have exactly the right capacitor so a preset pot is add e d to allow some adjustment . Before you know it the clock circuit is taking up more space on the board than you had hoped.  Providing the application does not demand a precise clock source a tiny 8-pin microcontroller may offer a better solution to the problem. It needs no additional external components and an old ATtiny15 can be found quite cheaply. Another advantage of the solution is that clock frequency adjustment does not involve changing external components and is not subject to component tolerances.  The microcontroller’s internal RC oscillator is already accurately calibrated to 1.6 MHz. With i...

This basic circuit is simple to create and the tool's are not critical . Most of them can be found in your junk parts box . The L1 antenna coil can be made by close winding 8 to 10 turns of 22 gauge insulated hookup wire around a 1/4 inch form such as a pencil . You can exeprement with the size of the copile and the number of  turns to see how it affects the frequency and singnal out put of the oscilatter . You ought be able to pick up its signal with a standard FM radio receiver . The signal in ought be coupled by a disc capacitor of about 0.1 uF to stage in main of it .