• on Test & Measurement
  • Published in issue 7/2009 on page 104
About the article

Digital Sweep and Sinewave Generator with direct frequency entry

Digital Sweep and Sinewave Generator with direct frequency entry
The Parallax SX28-based ‘Frequency Response Sweep Oscillator’ project published in the April 2008 issue of Elektor inspired the author to develop a similar circuit based on the ATmega48 microcontroller. As it turns out, the ATmega-based circuit is nearly as capable as the original. An important characteristic of the design is the maximum direct digital synthesis (DDS) sample rate that can be achieved when generating a sinewave.
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Characteristics

* Digital sweep function:
Frequency ranges: 100 Hz to 100 000 Hz or 50 Hz to 15 000 Hz,
logarithmic scale with 256 steps
2 sweep rates: 0.2 ms or 0.4 ms per frequency value
(phase accumulator increment value changed every 0.2 ms or 0.4 ms)
Outputs in sweep mode:
* sine output
* marker frequency (rectangular wave)
* marker position pulse
* trigger pulse at start of each sweep

* Digital sinewave operation:
Direct frequency entry in Hertz via keypad
Format: '*' = start of entry
digit(s) 0 to 9
'#' = end of entry, start sinewave generator
Outputs in sinewave mode:
* sine output (0 VPP to 4.5 VPP)
* frequency/marker pulse (rectangular wave)

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