February 13th, 2009

AVR FM transmitter

AVR FM transmitter

When it’s about FM transmitters most of the people think about complicated circuits with LC oscillators, tuning problems, pcb coupling issues and the high risk of failure. You can find dozen or more schematics on the web, I personally tried a few, but without luck because I couldn’t tune in the oscillator.

The mathematical background is complicated, but well explained for those interested, the code is written is assembler which is a must since the tight timing. Beside the inductor all of the components are widely available, this must be hand made and by stretching you can fine tune the oscillator, thing which will be probably needed.

By using surface mount components the pcb size could be greatly reduced, but keep in mind when making the layout to reduce coupling and noise susceptibility.

Make sure that you don’t disturb any local frequencies, or somebodies privacy with it.

AVR FM transmitter: [via] [Link]

 Elevator Voice Message Level Indicator

Have you ever been into a boring elevator ? with no sound and level indicator lights ? because I’ve been and i can tell you its not a pleasant environment to be in. Those elevators are sometime rebuild or renewed but the level indicator lights and some kind of sound system are not installed because of the high price tag, and possible need of rewiring. This project comes with a solution, and an easy to implement one.

It features a voice message system which inform you about the current level and optional about the next level. It needs no connection to the elevators system, its powered by batteries so you just need to stick it somewhere inside the elevator. If i would to build this system i would also include an FM radio, because most modern elevators include this features and i think its neat.

Elevator Voice Message Level Indicator: [Download Project][View Project PDF]

 USB Computer Control for the Hamtronics R139 WX Satellite Receiver

The Hamtronics R139 WX FAX Receiver is a 5 channel crystal controlled receiver specifically intended for reception of the polar orbiting weather satellites that broadcast on the 137 MHz weather band. The receiver has a wideband IF that allows for reception of the wideband FM signal from the satellites. The received audio from the receiver is passed to a computer sound card where a program such as WxToImg is used to decode it to an image.

The R139 can scan the 5 channels and automatically stop on an active channel. This works well provided one has a strong signal. If the signal is weak or subject to fading the squelch will close and the scan will resume during the satellite pass which results in a truncated satellite image. For reception of the satellite pass horizon to horizon manual selection of the received channel and running with open squelch is needed.

USB Computer Control for the Hamtronics R139 WX Satellite Receiver: [Via][Link]

One transistor super-regenerative FM receiver - top board view

the author writes: Radio Shack Special…the name was given to it because all of the components may be purchased at your local or nearby hardware and Radio Shack store. Although Radio Shack does not carry a typical 6 lead AM/FM variable (tuning) capacitor for tuning in to all the FM stations, I have managed to come up with a simple little way of going from station to station by just stretching and sqeezing the DRAIN coil with some sort of non-metallic small stick; such as a tapered-wooden match-stick.

If you would prefer to use a variable (tuning) capacitor, you can always find these devices from any AM/FM tunable (not digital) radio or check to see if your local Wal-Mart carries a small blue portable AM/FM radio by ‘Lenoxx Sound’, which sells for around five dollars. From that radio, you can the salvage the variable (tuning) capacitor (with the plastic knob included), the headphones (in which I use for the Radio Shack Special) and the audio jack (also what I use for the project). A good buy for $5. The finished PCB in this project is adapted to either use a variable capacitor or not.

One transistor super-regenerative FM receiver: [Link]

    What is PCI MAX 2007?

    PCI MAX 2007+ is a computer card that will change the way you listen to your MP3’s or other audio via PC. It will effectively change your PC into a stereo FM radio station; it is a small digital FM transmitter in a form of a PCI PC card. You will be able to play your audio files (CD, wav, MP3, real audio etc.) from your PC through radio waves directly to your household radio receiver in the next room, in the living room, across your yard, in whole block of flats….or for the entire village/small city. You need just an ordinary radio receiver to receive your signal. The included software (also available in the support section of this website) lets you set the frequency and the output power. You can either service your living room, garden or an entire community.

FM transmitter PCI MAX 2007FM transmitter PCI MAX 2007 antennaFM transmitter PCI MAX 2007 LCD moduleFM transmitter PCI MAX 2007 LCD moduleFM transmitter PCI MAX 2007 LCD module

    PCI MAX is really easy to install, just like any other PCI board on your computer you just plug it in and you install drivers and software that are provided with the board. The Software gives you full control over frequency and power. But if you need Additional output power and superior audio quality you can obtain it by using external power source.

Technical specifications:

  • Frequency band: 87.5 (86) -108MHz FM BAND, 50KHz steps
  • Stereo mode with excellent stereo separation
  • Stereo 3.5 phono socket audio input, jumper cable included
  • RDS functionality with optional RDS daughter board
  • On-board DC/DC converter for noise-free audio
  • Frequency, mode and RF output power adjustment with a click of a mouse (Windows) or with LCD module
  • RF output power: >2500mW (2.5W), depending on the model

You can get full specifications and other details at PCI MAX 2007 page

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