Thursday, September 17, 2015

Project Signal Generator

I've thought about making a function generator for quite a while now - I've even tried, and failed, to make one in the past.  Currently my motivation to make one is due to wanting to find out what the actual resonance frequencies are for my different Tesla Secondary Coil and Top Load combinations and so I can design and make a Dual Resonant SSTC.  I can calculate predicted resonant frequencies using tools like Deep Fried Neon TC Calculators but this does not provide actual values (parts all have tolerances - actual values can differ by a certain percent).  Being able to match frequencies using actual measured resonance frequencies becomes important with DRSSTC's (regular SSTC's only have a single resonance circuit and the primary tank circuit can self tune with feedback).   To be able to find these resonance frequencies I'll need an actual function generator to generate signals to determine actual values.

What is a Signal Generator (Wikipedia link) - basically a signal generator is a device that can produce waveform's (like sine-wave, square-wave, triangular-wave, saw-tooth-wave's) at various frequencies. Commercial signal generators are fairly expensive- unless you are lucky enough to run across older ones for sale (I have not been that lucky yet - I keep looking though).
Since a commercial model is out my price range I've been researching methods to make one, that can actually produce the frequencies that I need for my Tesla coils - about 200kHz).   Square waves are fairly easy to produce with either 555 timer chips or micro-controllers, the others are a bit tougher to produce.

I have found a number of methods that may work using specific IC's designed as Signal Generators, Op Amps configured to produce different signals, function libraries for Arduino micro-controllers (audio signal generation), and DDS (Direct Digital Synthesizer).

I am currently working on all of these approaches and I will update my results with each after I get each one functional.

Resources (datasheets, etc.):
LM348-Signal Generator
XR2206 Monolithic Function Generator IC
MAX038 Waveform Generator
ICL8038 Precision Waveform Generator
AD9850 (DDS IC)
(the first 3 are discontinued products but are still available on ebay)

UPDATES on the above Signal Generators
AD9850 part1