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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.



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Last Updated on Wednesday, 21 September 2011 00:21
 
Grave popper
Written by Administrator   
Tuesday, 20 September 2011 00:00
For those of you who love Halloween and want to build scary machines, now is the time to start.

 
RepRap Mendel build log
Written by Dangerus Prototypes   
Monday, 19 September 2011 00:00

Authors: Dangerus Prototypes

NBitWonder documented a RepRap Mendel 3D printer build:

While the DIY websites have been abuzz about the Ultimaker 3D printer, I’ve been hard at work constructing a RepRap Mendel.  I’ve been doing my best to document the complete build process as well.


Last Updated on Monday, 19 September 2011 02:09
 
How to build a DIY laser cutter gas containment chamber
Written by Electronics How-To Videos & Articles « Wonder How To   
Friday, 16 September 2011 00:00

If you are the proud owner of a laser cutter, you had better be careful with your expensive new toy. Some materials can damage the optics in your laser or produce poisonous gas when you cut them, so you need to make a gas containment chamber to work in. Watch this video to find out how to do that out of silicon wafer, silicone sealant, and a metal cookie tin lid.

Read more: http://www.wonderhowto.com/how-to-build-diy-laser-cutter-gas-containment-chamber-408854/

Last Updated on Friday, 16 September 2011 00:54
 
PIR Motion Detector
Written by admin   
Friday, 16 September 2011 00:00

Authors: admin


This project demonstrates how pyroelectric IR sensor can be applied in the detection of moving object. Passive IR detector does not emits any IR light by itself. It is triggered by the variation of IR light that comes from warm & moving objects such as human body. Dogs, cats & other household pets have smaller bodies & do not radiate sufficiently strong IR to trigger the detector. Therefore it is pretty well immune to false alarm caused by pets.

PIR Motion Detector - [Link]

Last Updated on Friday, 16 September 2011 01:03
 
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