AD9850, a Direct Digital Synthesizer IC

If you search on eBay for AD9850 you will find a lot of modules equipped with this nice DDS (Direct Digital Synthesizer) IC. Most of those modules incorporate a 125 MHz Xtal oscillator. The modules are offered often for less than $5.
With this module you are able to build your own sine/square wave generator
that runs from 1 Hz till 40 MHz in steps of 1 Hz.

There is some control required. Homebuilders often use a PIC (for example 16F628A).

VK5TM describes some AD9850 generators on his website. Here you will also find the
required hex files for PIC programming:


http://www.vk5tm.com/homebrew/dds/dds.php

Some specifications for the AD9850 chip:

The AD9850 is a highly integrated device that uses advanced DDS technology coupled with an internal high speed, high performance, D/A converter and comparator, to form a complete digitally programmable frequency synthesizer and clock generator function.
When referenced to an accurate clock source, the AD9850 generates a spectrally pure, frequency/ phase-programmable, analog output sine wave.

FEATURES and BENEFITS

    125 MHz Clock Rate
    On-Chip High Performance DAC and High Speed Comparator
    DAC SFDR > 50 dB @ 40 MHz AOUT
    32-Bit Frequency Tuning Word
    Simplified Control Interface: Parallel Byte or Serial Loading Format
    Phase Modulation Capability

    3.3 V or 5 V Single-Supply Operation
    Low Power: 380 mW @ 125 MHz (5 V)
    155 mW @ 100 MHz (3.3 V)
    Power-Down Function
    Ultrasmall 28-Lead SSOP Packaging