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Regular diode used as a photo-element
Written by Administrator   
Friday, 30 September 2011 00:00

robertgawron.blogspot.com writes:

There are special diodes, that are designed to measure light intensity, also regular LED can be used for this, but I was wondering, if any diode is suitable here? In this post I will share results of those experiments.

Theoretical background of this is well described in Wikipedia: “A photodiode is a PN junction or PIN structure. When a photon of sufficient energy strikes the diode, it excites an electron, thereby creating a free electron (and a positively charged electron hole). This mechanism is also known as the photoelectric effect. [...] Since transistors and ICs are made of semiconductors, and contain P-N junctions, almost every active component is potentially a photodiode.” [source]

Regular diode used as a photo-element –[Link]

Last Updated on Friday, 30 September 2011 01:19
 
The FM Transmitter Bug
Written by Dino Segovis   
Wednesday, 21 September 2011 00:00

Authors: Dino Segovis

Building an FM transmitter is fun! This kit was very easy to build so it would be a good first time kit if you’re just getting started in electronics. If you can understand how to read capacitor and resistor values and you can solder, you can build this kit. If you’d like to build one they can be purchased from these vendors:
http://www.hobbyengineering.com/H1481.html
http://www.hobbytron.com/Mini-FM-transmitter-3-Volt-FM-Transmitter-bug-kit.html.

My Friend John S. gave this kit to me recently and I thought it would be a good Hack A Week project. There’s some good electronics to learn about here: class C amplifiers, FM transmission, VHF antennas, positive and negative feedback, stray capacitance, and induction.

The circuit is basically an audio amplifier that modulates a radio frequency oscillator tuned around 100 MHz. Output from the collector of the amplifier transistor is fed into the base of the second transistor where it modulates the resonant frequency of the “tank” circuit (the 5 turn coil and trim capacitor) by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor. The tank circuit is connected to a Hartley oscillator circuit.

I was able to receive transmissions out to 30 meters and that was going through a metal garage door. The range can be greatly extended by using a dipole antenna rather than the half wave antenna. Connect the dipole to the circuit with a 50 ohm coaxial cable. Connect the center lead to the antenna point on the circuit and the outer shield to earth ground. I’ll be experimenting more with this.

Have fun building this and keep on hackin!


Component list:

Resistors: (carbon, 0.25 W, 5%)
1 – 1Megohm
1 – 47K ohm
1 – 22K ohm
1 – 10K ohm
1 – 470 ohm

Capacitors:
1 – 1n ceramic #102
1 – 5pf ceramic
2 – 22n #223
1 – 27pf ceramic
1- 100n monoblock

Other stuff:
2 – BC547 transistors
1 – 5 turn coil (make sure you separate the windings so they don’t touch each other)
1- Electret microphone
1 – tripcap, yellow (6 – 45 pf)
165 cm antenna wire
Battery holder, 3v – 9v.



via:

Last Updated on Wednesday, 21 September 2011 00:21
 
Arduino TNC
Written by Dangerus Prototypes   
Friday, 05 August 2011 09:00

Authors: Dangerus Prototypes

Amateur radio operators use various digital data modes for radio communications. One such mode is known as packet radio, which transmits data in groups or “packets” of bytes. As described by the ARRL, “packet radio allows improved throughput and error control. The basic protocol for packet radio is AX.25. Transmission speeds typically range from 300 bps on the HF bands to 1200 and 9600 bps on VHF or UHF.” The necessary interface hardware between the radio and the computer is known as a Terminal Node Controller (TNC).

KI4MCW reports on the status of his project to implement a TNC using the Arduino:

The goal of this project – the creation of a simple but effective TNC using Arduino hardware – has been achieved a couple of different ways. Because of the precise timing required to sample and decode AX.25 audio, it was not possible to build a working solution using the standard Arduino libraries. Instead, each solution has involved software written in C, calling AVR-libc libraries or manipulating register values directly.

Currently, my efforts are focused on an implementation that uses the freely available BeRTOS package, a collection of integrated libraries and drivers for embedded platforms. The AX.25 and AFSK modules included with BeRTOS form a high-performance packet engine that can be modified to function as a KISS TNC. I am working with the BeRTOS team to integrate KISS functionality into the main package, so hopefully those functions will be available in future versions of their product.

Progress reports and a working example of the code (both source and binary for an ATmega328p-based Arduino) can be found at the KI4MCW website. A simple test circuit is available from the BeRTOS website.

Read more: http://dangerousprototypes.com/2011/08/05/arduino-tnc/

Last Updated on Saturday, 27 August 2011 03:31
 
G17339 – Russian Geiger Tube Schematic
Written by Administrator   
Wednesday, 03 August 2011 00:00

G17339 – Russian Geiger Tube Schematic –[Link]

Last Updated on Wednesday, 03 August 2011 18:43
 
Audio Sine Wave Generator
Written by admin   
Thursday, 28 July 2011 00:00

Authors: admin


This project is a sine wave generator which is based on the Wien Bridge Oscillator and produces low distortion sine waves in the range of 15 Hz up to 22KHz in two ranges. The two output voltage ranges are from about 0-250mV and 0-2.5Vrms. The circuit is based on TL082 dual operational amplifier.

Audio Sine Wave Generator - [Link]

Last Updated on Thursday, 28 July 2011 01:23
 
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