Here's how to build your own adjustable power supply based on LM317. The IC LM317 is so versatile that an almost unlimited number of different, small, high grade power supply circuits can be built using it. The configurations can be introduced for different applications for upgrading an existing unit with features that would virtually make it indestructible.
A few useful application circuits using IC LM317, collected from National Semiconductor's PDF datasheet are meticulously explained in this section with the help of the relevant circuit diagrams. All the circuits discussed below require an unregulated input voltage (max. 35 Volts) from any standard transformer/bridge/capacitor network.
Posted on Wednesday, March 20, 2013 • Category: FM Transmitters
This tutorial is for making simplest FM transmitter using only one transistor. VC1 is a small, screw-adjustable, trimmer capacitor and its rating should be around 10-100pF. Set your FM receiver for a clear, blank station. Then, with a non-conductive tool, adjust the capacitor for the clearest reception, rotate it till the receiver receives a sound from the microphone of transmitter. Use the following formula for determining the frequency.
Posted on Friday, March 15, 2013 • Category: AM Radio
VHF FM Aircraft Receiver is a superregenative receiver developed for listening to FM transmitters but also tunes the aircraft band and the top portion of the FM broadcast band. Receives both AM and FM (107mHz to 135 MHz). You can use this receiver with the any FM transmitter. The receiver is amazingly simple using only one transistor for the receiver section and one IC for the audio section. This circuit is a self-quenching regenerative RF receiver also known as a superregenerative receiver. A superregenerative receiver performs two basic functions. First it feeds back a portion of the received signal from it’s output in phase to its input; and second a super audible quenching oscillator drives the amplifier through the point of oscillation and maximum sensitivity and then quenches the oscillation repeatedly. This keeps the feedback from driving the circuit into self-oscillation and allows the signal to be regenerated over and over again. In this version of the circuit, both functions are performed by the circuitry associated with Q1.
The rest of the circuit, shown to the right of L3 in the schematic, comprise the audio amplification circuit and are centered on the LM386 Audio Amp IC. In this configuration the LM386 is set at a gain of 200 and feeds it’s output to a standard 1/8-inch diameter stereo phone jack. The audio can then be heard by plugging any standard stereo headset into the jack.
Posted on Monday, February 25, 2013 • Category: FM Transmitters
For months I’ve been looking for a simple FM BUG project, the ones online require inductors which you either have to acquire or build, if you don’t have a LCR meter it becomes rather hard to get the circuit working, specially if you’re a beginner without an oscilloscope! – Sometimes they don’t even tell you which inductance is required and you have to calculate an estimate, which is the main reason why many high frequency RF projects fail in the first place. This circuit on the other hand performs pretty well, even if you’re manipulating the board or touching the coax it will stay within the tuned frequency (unless you touch the transistor or timing capacitor!).
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