I prototyped a 0-6VACrms AC Sine Wave Generator Module (AC-coupled, bipolar output) shown in the below schematic.
Specs:
POWER SUPPLY (not on schematic): Single Supply 12VDC Regulated with on-PC board -12VDC Charge Pump Inverter, ICL7662. Maximum ripple on +12V rail is 600uV. Maximum ripple on -12V inverter rail is 900uV.
Principle of Operation: (per accompanying schematic & sequence of photos)
CD4047 provides a precise 50% duty-cycle, 100Hz square wave on +12V power so, it is a unipolar output 0-12V.
That output is AC-coupled and level-shifted by OA#1 to swing +/-12V to produce a bipolar 24V Square Wave.
OA#2 Integrates that square wave into a Triangle Wave which is then fed to OA#3.
OA#3 Integrates the triangle wave into a Sine Wave which is fed to OA#4.
OA#4 Amplifies the Sine Wave to the desired 6VACrms (minimum) bipolar output required.
Objectives:
1) Most important, operation from a single, well-regulated +12VDC power supply. (May also be operated from a single 9V battery with slightly reduced Sine Wave amplitude output.)
2) Precise 50% duty-cycle square wave so, CD4047 was chosen. Op Amp square wave oscillators tested are too sloppy and imprecise.
3) Dual integrators provide the easiest, most stabile method for producing a low-frequency, low-distortion sine wave while allowing the use of non-critical component values. Phase shift oscillators and shaping filter schemes are too finicky and too complicated. I like simple.
4) Amplitude stability to 0.5% is very important. It is entirely dependent on the +/- rail voltages so the need for input voltage regulation is critical. An on-PCB MC7812 seems adequate. No temperature compensation or AGC is provided because the parts count goes way up along with the module's complexity and resultant BOM cost.
HELP NEEDED: Open to any suggestions/criticisms/advice/revisions/corrections/re-design, etc. that could make this a better, low-cost product aimed at the student, beginner, hobbyist, DIY Homeowner markets.
What good is this thing and what is it used for? Well, for those millions of people who have bought cheap DMM's and want to know whether their AC functions are working at least on the low voltage AC range(s), an economical AC Sine Wave module may be something they'd be interested in along with an economical DC reference and a precision resistor module.
Hell, they could verify that their cheap little DMM is worthy of trusting around the house, garage, hobby bench or, even coursework at school. Or, maybe if it
s not, buy a real DMM.
By the way, I'm an admirer of the DMM Check product but, it's too good and too expensive for the market I'm speaking of here.
Thanks in advance for looking things over. SWING AWAY....