A basic Wien Bridge Oscillator using a filament lamp with an op amp. It is a property of filament lamps that the resistance of the tungsten filament increases in a non-linear manner as the filament heats up. The lamp in Fig. 3. 4. 1 is connected in the negative feedback potential divider that sets the gain of the non-inverting ampli
Click here to download the full size of the above Circuit.
fier. The gain of the amplifier is set by: Therefore the greater the resistance of the lamp the lower the amplifier gain. By choosing a suitable lamp, the gain of the amplifier can be automatically controlled over an appropriate range. Usually a lamp with a maximum current flow of around 50mA or less is used, to give an initial gain of more than 3 as the oscillator starts, falling quickly to 3 as the lamp heats up. Hewlett`s original 1939 design used a high voltage vacuum tube (valve) and relatively large lamp, with modern low voltage semiconductors however, it is not easy to find suitable filament lamps that have a suitable voltage range and a low enough current to avoid overloading the amplifier, although useful lamps can still be found, usually of the wire ended T1 or grain of rice` types but even they are becoming more difficult to find in component suppliers catalogues, as LED types become more popular for low voltage lighting. Fig. 3. 4. 2 shows a low current filament lamp designed to work from 5V at 45mA, and Fig. 3. 4. 3 is a graph taken from a typical example, showing how its positive temperature coefficient resistance varies with voltage. (Note that resistance without any temperature dependant characteristics would be a straight line). The useful area of the lamp characteristic, where the largest change in resistance occurs is shaded green, the oscillators amplitude is stabilised by making use of this area....
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: