A homebrew 2M transceiver I wanted to use it mobile so I wouldn`t have been able to use a fist mike. I had the bright idea of using one of those cheap personal hands free kits you can buy for mobile phones, however once installed reality struck home - hardly any audio! Like the microphone amplifier of many Ex PMR radios and lowcost hand helds, the circuit
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I used had fixed amplification. Gain could be increased but it would then lead to the problem of distortion if the microphone position changed or I shouted to get over vehicle noise. The simple circuit described here gives additional gain so increasing the microphone sensitivity, enabling low cost mobile phone accessories to be used and also adds AGC (automatic gain control) action. Whilst developing the circuit it was obvious that the same design would make a good desk microphone, the prototype allowed me to obtain good quality audio from anywhere in the workshop. A few years back one of my transceiver designs incorporated the Plessey VOGAD IC type SL6270 to good effect, unfortunately they now seem to be deleted from distributor`s lists. This design is not totally original with elements previously being used elsewhere1, but it does provide a cost-effective alternative to the Plessey solution. Figure 1 shows the circuit diagram, IC1a amplifies the incoming microphone signal with the gain set by R8 and the combination of R9 and the drain / source resistance of Q1. Minimum negative feedback hence maximum gain occurs when Q1 is at minimum resistance. The output from IC1a at pin 1 is applied to the voltage doubler circuit of C2, D1, D2 and smoothing capacitor C3. This feedback voltage is applied to the gate of Q1. Minimum source to drain resistance occurs when the gate is at (or below) the source potential, as the op amp AC...
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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