The three-transistor circuit in Fig 1 costs less than $10 to build, uses commonly available components, and consumes less than 10 mA from a single 9V battery. If you wind coil L1, as the figure shows, the circuit receives signals in the 5- to 15-MHz short-wave band. You can add turns to or subtract turns from L(or change C2) to receive other frequ
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encies. Q1, a 10 bipolar transistor, acts as a high-gain regenerative stage and amplifies microvolt-level signals at the antenna up to hundreds of millivolts to drive diode-detector D1. In addition to providing high gain, regeneration also greatly increases the Q (selectivity) of the circuit, producing a high-Q circuit, which can use low-cost coils (or free hand-wound coils). Using a high-transconductance bipolar transistor for Q1 rather than a vacuum tube or JFET provides much more gain per microamp of current. However, in previous bipolar circuits of this type, the regeneration level has been difficult to control. In this circuit, R1 and R2 provide a large amount of negative bias at the emitter of Q1 to achieve smooth control. Rallows for user control of the regeneration. You should adjust the pot so that Q1 is just at the threshold of oscillation where both gain and selectivity are maximum. Q2and Q3, a two-transistor amplifier, which has sufficient output level to directly drive headphones or a small speaker, amplify the detected audio signal output from D1. R3can become a volume control if you replace it with a 2-kOhms potentiometer and connect C3to its wiper. R4 and C4 form a lowpass filter that maintains circuit stability and improves the receiver`s sound quality. D2, D3, and D4 implement a low-cost voltage regulator to keep the voltage supplying Q1fairly constant, which minimizes drift. This receiver works with a...
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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