JFET input. PN photodiodes such as the popular `bullet cell` put out an extremely low-level signal. Yet photodiodes offer advantages over phototransistors. For example, more rapid response to motion. Also, some photodiodes have a peak response in the range of visible light. On the other hand, most phototransistors provide peak response in the infrared. For color reproduction, flat visible light response is essential.
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Anyway, with photodiodes, a high-impedance preamplifier is even more important than it is with phototransistors. For such applications, the JFET is the amplifier of choice. A JFET is only a little more difficult to work with than is a bipolar transistor. Yet a JFET is more sensitive than either a bipolar transistor or a vacuum tube. Since the output of the photodiode is a high-impedance signal, the JFET is a helpful idea. A JFET adds complexity, but will probably save you a few amplifier stages. Coupling. The high-Z (high-impedance) transistor preamp allows resistance coupling (actually "resistance-capacity" coupling). In their amplifiers, the television pioneers used this same, resistance coupling. Because of their very limited drift, resistance-coupled amplifiers tend to be stabler than direct-coupled amplifiers. The low impedance inputs in normal transistor preamplifiers require electrolytic capacitors in the coupling network. When new, these capacitors are dreadfully leaky. As the capacitors age, the leakage only increases until it destroys the bias voltage on the transistor. At that point, the transistor will block and quit operating. Even before the bias deteriorates, the capacitor can visibly alter television signals. Yet with a high-impedance preamplifier, you can avoid electrolytic capacitors. Instead, insist on premium capacitor, such as the mylar or polyester types. Bypass. Coupling and bypass capacitors don`t...
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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