The very small DC voltages at the output of the diode detector are difficult to amplify accurately. DC offsets introduced by any op-amp are the main culprit. Low frequency noise (1/f noise) is another. Chopping the DC with MOSfet switches is an excellent way to get around these problems. In the circuit below, a chopper integrated circuit ( LTC1043
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) switches between two square-law detectors: one detector gives a positive-going voltage and the other gives a negative voltage. Cosc sets the (square wave) chopping frequency to about 90 Hz - you want to keep this chopping frequency fairly low, but well away from 60Hz and 120Hz. The op-amp that follows the diode chopper has a gain of 181, and amplifies the 90 Hz. square wave that the chopper provides. Any offset that the op-amp adds is eliminated by the de-chopping switch at its output. The RC network (R3, C3) at the output is a low-pass filter, and sets the bandwidth at about 10Hz. This allows reasonably fast meter response, while eliminating noise. A second op-amp acts as a conventional DC amplifier, and boosts voltage to drive an external meter. Gain can be adjusted (1+ R6/R7) to provide a reasonable output range for your meter. This op-amp`s input offset voltage is amplified by the op-amp`s gain, and appears at the output. If gain is high, this can be a significant offset from true zero. What`s the sensitivity limit of this circuit The primary source of noise is the warm 50K resistance of the rectifying germanium detector diode. The op-amp shown adds about 10nV/rt(Hz) as well. Within the 10 Hz. bandwidth, thermal noise of the 50K detector resistance is about 0. 1uV. At -60 dBm input RF voltage, the detector diode generates about 0. 1uV DC voltage, so inputs less than -60dBm are lost in noise. A narrower filter (<10Hz)...
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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