Wiring circuit

This schematic diagram show a single chip Theremin circuit.  Theremin is an electronic music instrument which sense hand movement to control the tones/frequency.  This Theremin circuit uses two separate Colpitts LC oscillators to produce a beat frequency. 

The frequencies of  two Colpitts LC oscillators are mixed and then rectified. This rectification  demodulate the mixed signal to get the beat frequency which is in audible range. This beat frequency or difference is the real  Theremin’s output. The oscillator is operated at high frequency (inaudible) to get wide audible frequency range of beat frequency when two oscillator output is mixed.  This circuit uses a 4011 quad gate to construct the high frequency oscillator operating at 250kHz. Here is the schematic diagram of the circuit.

The metal probe that is used to sense your  hand produces only small frequency shift in term of percentage of original frequency, that’s why we need to derive the beat frequency to get wide audible frequency range as the result of  high frequency shifting. The IC2, an LM741 is used to amplify the mixed signal before rectification. 

The D1 will  rectify the mixed signal to detect the audio (the beat frequency).  This audio signal is then filtered by an adjustable bandpass filter IC3. The further audio amplification before power amplifier IC5  is done by IC4. The metal toilet-tank float  is used for the hand probe since is has better sensitivity than a simple wire antenna, but any conductive material will work.

This is a complete AVR Tutorial, including avr programming in a very basic & organized way, We will go through by following items.

Click Here is one for Windows

The best way to explain what a microcontroller is, is to start with your computer. Your desktop computer (or laptop) is comprised of multiple parts, a CPU (such as a Pentium or Celeron), some RAM, a hard disk, a keyboard and mouse and a monitor Lcd. Programs are stored on the hard disk and run on the CPU, with temporary data stored in RAM. You can run multiple programs at a time by having one ‘master program’ called an operating system (such as Linux, Windows or Mac OS X) and that master program keeps track of things for you.

The AVR chip has components, too. It has a CPU, some flash storage, some RAM and some EEPROM, all in one little chip!. The CPU is just like the one in a computer, but its much simpler and not nearly as fast (what do you expect for $2.50?) The flash storage is just like the flash storage in your mp3 player or digital camera card, except its used to store programs. Its kinda like the hard disk of the microcontroller, except you can only read from it. The RAM is just like computer RAM. The EEPROM is kinda like flash except you cant run a program from it, but its used as long term storage. The EEPROM doesnt get erased when the chip loses power.

So, to recap: The AVR chip runs whatever program is stored in the flash, uses the RAM for temporary storage and the EEPROM for longer term storage.

Most computers have a 32-bit CPU running at 1GHz, with 1GB of RAM and 100 GB of storage. The kinds of micro-controllers discussed here run at 10MHz, have 1KB of RAM and 10KB of storage. (On the order of) However, their small size, lower power consumption and low cost make them an excellent choice for many projects!