/diy/ - Do It Yourself

[Anonymous No.1610110]

Is there some super pure sinewave generator that has a huge range (tuneable with a potentiometer, not by changing caps)? I need one.

[Anonymous No.1610115]

Yes

Is expensive

Google

[Anonymous No.1610116]

>>1610115
>Google
hurrrrrrr why even have a forum

i meant for audio use, not calibration or anything. and diy.

[Anonymous No.1610121]

>>1610116
>- First ask Google, then ask /diy/. Your question will probably be better received if you do so.
fuck you faggot.

[Anonymous No.1610124]

>>1610121
oh you dont know an useful answer. its all cool.

ill wait for someone more knowledgable to come by.

[Anonymous No.1610127]

>>1610124
I've built one, it's not insanely accurate, you're not going to DIY one that is highly clean and dead on though.

Also read the forum rules. Not only does Google have a super fast and easy answer, but there is already the /ohm/ thread that will get you higher traffic for the question

[Anonymous No.1610171]

Pull apart a tuner radio for the varicap??

[Anonymous No.1610172]

>>1610110
if you know how to solder/breadboard you could just string a fuckload of voltage controlled bandpass filters in front of a noise generator. With that you have as pure of a sine wave as filter stages you can afford and they're all controlled by a one-gang pot. White noise is defined as equal energy at all frequencies, and every bandpass stage gets you closer to selecting a single frequency from the whole range. LM13700 is cheap, adequate for audio frequencies, and is tunable over many octaves if set up right.

[Anonymous No.1610277]

>>1610110
Adjustable/swept/whatever you want triangle wave gen (loads of topologies to pick from, don't restrict yourself to pic related) plus a diode waveshaping circuit will give you sine wave output with like 1% THD. Having a filter on the output that can track with the input frequency can reduce that but will increase cost and complexity.

>>1610171
The small capacitance of most varicaps doesn't make them a great choice for audio frequency filters. Requires large resistors for RC filters which increase output impedance and losses if the next stage doesn't have an even higher input impedance. Great choice for RF, bad for AF.

[Anonymous No.1610296]

>>1610277
Thank you for the insight, honestly.
Good to know :)

[Anonymous No.1610301]

>>1610277

somebody who actually knows stuff, on /diy/. imagine that.

[Beppu No.1610392]

>>1610301
Avril lavigne?

Didnt think she was MAGA. Alt... but alt-right?

[Anonymous No.1610431]

>>1610110
yeah for something so inherent you'd think there'd be a solution, but I have not found one after a year (and viewed tens of thousands of ckts), so I am an expert on the absence of this topic (working on one now, to an extent)
There's two answer to your question:
yes, if you want to buy one called pre-built function gen
no, for diy, esp based on 'pure' and 'huge range'. These are mutually exclusive for a given function gen circuit.
Oh, to be specific though there are chips for this purpose only: go to analog devices and look for DDS based chips, theres one for less than 5 bucks (-> 25MHz) which typically use SPI (if tard, means you just need chip and arduino). In DIY nature, feels like cheating to me.

You're otherwise limited to :
DDS in general; ie buy a DAC that uses parallel port (i'd imagine you'd get higher speeds) or SPI, buffer with op-amp; this is what all new gennys use (dedicated RAM straight to DAC/FPGA)

Sine-Shaper network: feed in triangle (~6% THD), get sine. diode based one is honestly just ok, but the one I'm working on is converting it thru a diff pair looking fella (complicated topic) and I'm not gonna act like I know it works (but 10x better distortion, with 1/5 parts). (google sine wave generation techniques app note)

RF type, cap switching. probs not as bad as you think, you can get a single switch where you just solder the caps on point-to-point

ok I'm done answer for the day.

>>1610277

what book homie?

[Anonymous No.1610433]

>>1610277
I'd like to point out that this isn't a pure sinewave circuit like you'd get from an LC oscillator. If you look at the waveform under a scope you'll see it's a sequence of eight straight lines roughly approximating the shape of a sinewave. It starts with a triangle wave then uses the four diodes in the bottom right to flatten out anything above 1.4v and below -1.4v. The other two diodes reduce the slope for anything above 0.7v and below -0.7v. This type of circuit is called a clipping waveshaper. There are better versions of it that use more diodes and resistors to adjust the triangle slope at several points to more closely match a sine wave.

I'd suggest using the ICL8038. It's basically everything in that picture built into one chip and with a waveshaper that adjusts the triangle slope at sixteen different points. Unfortunately they're no longer manufactured and there aren't any similar alternatives so you have to use ebay. Everybody uses DDS chips like the AD9837 now. Those are a high resolution DAC being fed by a sin table ROM. You need to use a microcontroller to control them.

[Anonymous No.1612377]

>>1610431
Applied Electronic Instrumentation and Measurement by David M. Buchla and Wayne McLachlan

[Anonymous No.1612421]

>>1610110
XR2206 kits are dirt cheap. Complete audio in one range.