The multiplication operation that is required to generate a signal of a frequency equal to the difference of the input frequencies, can be implemented in several ways. Actually a multiplied signal generally also appears when two signals are added and subsequently put through a non-linear device, like a pn-junction in a diode or transistor. Example
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s of this type of mixer are a transistor biased into non-linear operation, a simple two-diode mixer and more advanced four-diode balanced mixers. When using a square wave oscillator, the multiplication operation simply comes down to reversing the polarity of the bat signal at the frequency of the local oscillator. This can be implemented by using an analog switch to switch between the bat signal and an inverted version of the bat signal. In the picture on the right a basic implementation of this idea is shown. The leftmost opamp is configured as an inverting amplifier to give the signal some extra boost. The rightmost opamp is an inverting amplifier with gain -1. A 4053 is used to switch the output to either the output of opamp 1A or opamp 1B. The positive inputs of the opamps are biased at half the supply voltage. These can be built with a single opamp or a NE555 (pdf) for example. In these type of oscillators, the frequency is inversely proportional to the RC product. The nonlinear (inversely proportional) relationship between the RC product and the frequency is not very convenient. This can be alleviated somewhat by using a logarithmic potmeter, but in that case the clockwise position of the potmeter corrresponds to the lowest frequency. These use a resonant LC-circuit to generate a relatively pure frequency (little harmonics). Disadvantages are the nonlinear relationship between LC and frequency and the lack of variable...
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.....
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