Once the circuit gets current, all variables are initialized and the loop function is continually running. Initially all LEDs are off and there is no signal at the output. By pressing the signal switch, the first light that shows the most signal is at the output and the D0-D7 terminals give the appropriate signal which, when passing from the converter from digital to analog, outputs a triangular signal. Of the 2 potentiometers (frequency...
Lamp LI stabilizes the loop gain at higher frequencies while the limiting action of R2, CRI, and CR2 prevents clipping at low frequencies and increases the frequency adjustment range from about 3:1 to greater than 10:1.
A Wien-bridge oscillator can be made Vllriable by using two frequency-determining parts that are varied simultaneously at high tracking accuracy. High-quality tracking potentiometers or variable capacitors are, however, expensive and difficult to obtain. To avoid having to use such a component, this oscillator was designed to operate with a single potentiometer.
A 555 timer operating in the astable mode generates the driving pulses and two 4518 dual BCD (binary coded decimal) counters provide the square waves. A TL081 op amp serves as an output buffer-amplifier, and potentiometers Rl and R2 are used in order to control the pulse`s frequency and amplitude, respectively. The output-frequency range can be varied by changing Cx. For example, a value of 0.1 gives a range from about 0.1 to 30 Hz, and a...
In this circuit, a square wave is filtered by a high-order low-pass filter so that a -3-dB frequency will eliminate most harmonics of the waveform. As a result, the filter outputs a fundamental sine wave. This method is applied to generate a sine wave by using a switched- capacitor filter (MAX292) (see the figure). This circuit offers wide frequency range (0.1 Hz to 25 kHz),
A TTL counter, an 8-channel analog multiplexer, and a fourth-order low-pass filter can generate 10- to 25-kHz sine waves with a THD better than -80 dB. The circuit cascades the two second-order, continuous-time Sallen-Key filters within ICS to implement the fourth-order low-pass filter. To operate the circuit, choose the filter`s cutoff frequency,^, by tying IC3`s D0 through D6 inputs to-5 V or ground. The cutoff frequency can be at 128...
U1A, an op amp, oscillates at the frequency at which the phase shift in the Wien bridge network is exactly zero degrees. Changing bridge component values changes the oscillator frequency. In this circuit, we need change only the two resistors to do this. S1A chooses a value among Rl through R6, and SIB similarly selects a value from R7 through R12. U1A must provide enough gain to overcome losses in the bridge, but.not so much gain that...
That circuit is based on a 14-pin DIL IC capable of producing sine, square, triangular, sawtooth and pulse waveforms of high accuracy and stability. The frequency may be selected to be from 0.001Hz to 1Mhz, Frequency modulation and sweeping can be accomplished with an external voltage and the frequency can be programmed digitally by resistors or capacitors. Sweep range can be up to 40:1 or 1000:1 with a little less quality.
This circuit generates a good 1KHz sinewave adopting the inverted Wien bridge configuration (C1-R3 & C2-R4). It features a variable output, low distortion and low output impedance in order to obtain good overload capability. A small filament bulb ensures a stable long term output amplitude waveform. Useful to test the Precision Audio Millivoltmeter, Three-Level Audio Power Indicator and other audio circuits posted to this website.
The multivibrator is a common circuit that consists of an amplifier with both positive and negative feedback (Figure 1a). When the output is positive, the positive input terminal equals ½V+, and the voltage at the negative input terminal changes toward V+. When this voltage exceeds ½V+, the output voltage rapidly changes to V. The positive input terminal becomes ½V, and the negative input terminal changes toward V.
This Design Idea provides a simple, inexpensive, portable circuit as an alternative to a microcontroller to provide a wide-range source of low-distortion sine waves for audio-circuit design and debugging. Although sine waves from DDS (direct digital synthesis) offer greater stability and fewer harmonics and other spurious-frequency components, this more "retro" approach lets designers use Linear Technology Corp`s LTSpice freeware and hone...
Electronic applications such as distortion and communications measurements require pure (distortionless) sine waves as input test signals. Distortion contained in test signals causes two problems. First, the test signal distortion content must be calibrated so it can be subtracted out of the measurement. Second, processing a distorted test signal usually creates unique harmonics which cause false readings because they cant be calibrated out.
The circuit of Figure 1 produces an accurate, variable-frequency sine wave for use as a general-purpose reference signal. It includes an eighth-order elliptic, switched-capacitor lowpass filter, IC3, which uses a 100-kHz square-wave clock signal that microcontroller IC2 generates. (Any other convenient square-wave source is also acceptable.) The microcontroller receives its clock signal from a 10-MHz oscillator module. A voltage supervisor,...
Digital potentiometers are versatile devices; you can use them in many filtering and waveform-generation applications. This Design Idea describes an oscillator in which setting the resistance of two digital potentiometers independently programs the oscillation amplitude and frequency. Figure 1 shows a typical diode-stabilized Wien-bridge oscillator that generates accurate sine waves from 10 to 200 kHz.
This Design Idea presents a low-cost method of generating the basic 19-kHz pilot tone. The 19-kHz pilot tone comprises a baseband signal, and the L+R and LR signals consist of DSBSC (double-sideband-suppressed-carrier) modulation centered at 38 kHz. For a receiver to correctly demodulate the signal, the transmitted pilot tone and LR signal must synchronize at their respective zero crossings.
Many applications require a sinusoidal reference voltage synchronized to the ac line voltage. You cannot derive such a reference voltage directly from the ac line because the waveform of the ac line is distorted because of nonlinear loads connected to the line and because the amplitude of the line signal varies. Hence, you cannot use a simple step-down transformer to derive the reference signal.
In this circuit the gain is provided by a FET type op-amp. I have used an LF351, which may be hard to obtain, but the TL071CN or TL081CN may be used and have a faster slewing rate than the LF351. The Maplin order codes are RA67X and RA70M respectively. The wien network is a parallel combination of resistor and capacitor, in series with a serial R-C network. Regenerative feedback is applied from the op-amp output, to the serail R-C input and...
The circuit requires only one power-switching device, and you can use an analog or a digital signal to drive the switching device. The circuit also requires only a few components: a diode, a switching transistor or a MOSFET, an inductor or a transformer, and a capacitor. Further, the design`s circuit losses are low, and the switching device experiences minimal stress during operation. Figure 1 shows the basic circuit, and Figure 2...
Rectangular pulse generators, even at high frequencies, are easy to design. However, the design becomes more difficult if you need a signal that contains a precise number of periods with a sinusoidal shape. Although it is easy to produce a good sine wave, the difficulty is producing a signal with a precise number of periods. The signal has to start and stop exactly at 0V. The scheme in Figure 1 can produce one to 15 periods of a 20-MHz...
A recent Design Idea described a method for designing simple, high-frequency LC oscillators with few passive components (Reference 1). However, for best results, practical hardware design of a stable oscillator requires more parts and greater complexity. Figure 1 shows a stable, 18-MHz oscillator with automatically leveled output amplitude control and an output buffer that delivers a sine wave with low harmonic content (Reference 2).
To keep the gain constant, the circuit used an incandescent pilot light to provide AGC (automatic gain control). As is true for all incandescent bulbs, the pilot light has nonlinear resistance. When you turn on the circuit, the cold lamp`s resistance is low, resulting in high gain. As the gain increases, the resistance of the warming lamp increases. Thus, the lamp provides an AGC function.