Low frequency signal generator.

Jump to Latest
50AE

50AE

Member
Joined 2011
#1
Hi folks,

I'm looking for a sinewave generator driving a step amplifier for my inductance meter with the following requirements:

-Not necessarily enclosed, can be a PCB or kit. I'll integrate the generator within an inductance measurement rig.
-Frequency range: 10Hz up to 1kHz, adjustable. The frequency can be fixed, such as steps of 10Hz, 20Hz, 50Hz, 100Hz, 200Hz, 500Hz and so on. No need for small steps.
-Temperature stability. This is where I'm having trouble with a cheap chinese board featuring a XR2206 chip. The output tends to shift in amplitude and frequency at it heats and settles up.
-A figure of 0.5% THD is plenty enough.

There's always the option to just purchase a high quality function generator. However, considering I'll be integrating and only using it for an inductance meter and I rarely work with MHz signals, I don't find the sense of it.
 
#6
Thank you, Rayma. I love simple minimalistic solutions, because they're easy to repair and sometimes, stuff does blow up. Considering I need a few values of frequency only. Although I quoted up to 1kHz, I've only used 200Hz one of a hundred times. I would be more than content with 25, 50 and 100Hz, by building three separate PCBs.

The project is basically an LM1875 amplifier feeding a fixed amplitude and frequency voltage into a step-up transformer to generate a variable voltage up to 200V. That way, transformer cores are excited enough to give the realistic inductance reading. Flux density can be adjusted via the amplitude and not necessarily the frequency.
 
  • Like
Reactions: rayma
#7
Using a PTAT current source in a tri-wave oscillator along with a sine-wave shaping circuit (Courtesy: Adel. S. Sedra, Kenneth C. Smith, Microelectronic Circuits) would give stable low distortion sinusoidal waveforms at any frequency. The oscillator capacitor can be any stable kind like polyester, polypropylene etc. and switching between different capacitors would give different frequency ranges automatically, much like function generator.

1747070826456.png


1747070528283.png
 
Last edited:
#8
50AE said:
The project is basically an LM1875 amplifier feeding a fixed amplitude and frequency voltage into a step-up transformer to generate a variable voltage up to 200V. That way, transformer cores are excited enough to give the realistic inductance reading. Flux density can be adjusted via the amplitude and not necessarily the frequency.
Click to expand...

I think many here will be interested in your complete project.
 
You must log in or register to reply here.
Top Bottom