His oscillator sought to use resistors and capacitors instead of bulky low frequency LC tank circuits to generate audio frequencies. He obtained low distortion (<0. 5%) with the use of a two stage amplifier with enough negative feedback to set it`s gain to just 3, as required for oscillation of the Wien Bridge circuit. He used a light bulb to serve as amplitude detector and linear gain setting resistor for the fed-back amplifier
Click here to download the full size of the above Circuit.
. Hewlett credits L. A. Meacham with the use of the light bulb for automatic oscillator gain stabilization as published in the Bell System Technical Journal Vol 17, p. 574, 0ctober 1938. The Wien Bridge network was invented by Max Wien in 1891. This excerpt from Hewlett`s thesis shows half the bridge. At the resonant frequency with equal resistors and capacitors, the attenuation is 1/3 of the input voltage with zero phase shift. This means that if an exact gain of 3 can be provided from the output of the network to the input, we have a sinusoidal oscillator. The simplified circuit on the right shows the lamp that stabilizes the non-inverting gain of the fed-back amplifier to exactly 3x. The lamp resistance increases when a larger signal is applied to it. This means that if oscillations grow too large, the lamp resistance increases to reduce oscillation amplitude until a stable equilibrium is reached. At this equilibrium point, the RC-CR Wien network forces a gain of 3x at the fed-back amplifier, which is to say, it forces the lamp resistance to a value that yields an amplifier gain of 3x. In turn, the Lamp forces the Wien network oscillation amplitude. This lamp stabilized Wien bridge oscillator differs fundamentally from RF LC oscillators commonly used in Radio circuits in that the oscillation currents and voltages in the Wien oscillator always remain nearly perfectly sinusoidal. Typical RF oscillators with an LC tank...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
characters left: