Cheap Function Signal Generator from ebay

A wonderfully flawed product which shows many of the common pitfalls in designing a signal generator. Looks like a university term project pushed out into production

[amtpdb]

I am getting ready to buy one of these to use with my diy oscilloscope for hobbies. I am retired and just getting into electronics. Could you suggest fixes and parts to make this better. It would be a great learning experience. A video or mods would be great. Teach us!
Thanks for your time.
Don

[KeystoneScience]

If I may ask, what is the name of the connected that goes from the generator to the oscilloscope? I can't find the name of it for the life of me haha

[denizcancgsar]

Thank's for nice video.. The sine superimposed into the saw tooth might caused by the tolerances of R-2R ladder DAC..

[KnowName]

I got one of these thinking I would be able to manually sweep the sine wave with the knob (for SPL testing in car audio) as you may imagine I was quite disappointed with this unit especially because it has a constant buzzing sound and has Distortion at every volume level and on every setting basically its a piece of s***. Lol. Do you know what I would need to change out on this thing in order to have the manual sweep function? Could I change one of the knobs out with a potentiometer?

[j.p.saliven]

Hi! Thanks for presentation! It is not a big surprise what you show us about the line of signal. This is Digital and very cheap. Would you measure on your scope how accurate are the 1 Hz, 100 Hz, 1 Khz, 1 MHz and 8 MHz are?

[gvvq-piml]

Hi could you use this to inject a signal into a CB mic socket to check deviation, on a deviation meter....Fred UK

[tjones]

Great detail... Thanks
While I agree with the flaws, the device is under $20...
Wicked cheap and pretty flexible and useful for the price...

[pcfred]

Similar to a kit I bought recently at banggood, but different. For the price better than anything I can knock together on my workbench.

[superrodder]

the most important way to describe this function gen. is cheap, cheap, cheap.
but one thing you can always count on, u will only get what u pay for.

[superdau]

This is a tough call.

On one hand I can see all the flaws in the design. A missing filter that could have easily been done with passives. No protection for the opamp, so it dies at 50Ohm termination (every decent fgen should be shortcircuit proof). TTL output directly driven by the micro (at least it looks like it). Square waves/sawtooth waves that are far from it at higher frequencies (some of the sellers on ebay show the waveforms).

On the other hand I know how long I had to live without any way to generate these kinds of waveforms, because fgens were so expensive. And for under 20$ this one isn't bad. Although you can get other DDS modules/shield for which someone has already written an Arduino program which comes out at a similar price with for example better sine/square performance even at the tens MHz range, but misses triangle/sawtooth.

The question is: does a beginner know what he's getting into when he gets one of these and what the implications of the flaws are. Or is any fgen better than none?

[SpeccyMan]

I bought one of these for its curiosity value (I already knew it was total crap.) The one I received came with another "undocumented" feature. The fuses in the micro-controller had not been set correctly so it was outputting at exactly half the displayed frequency. Soon fixed with a programmer but it sure is pretty piss poor quality control.

[Joerg]

Many Thanks from Berlin, Germany :-)
Best Greetings Jörg, DL7UJW

[jon]

I mainly repair analogue amplifiers, would this be ideal?

[nlbv]

Thank you for the great video! I got one of these and was a bit lost with absolutely no docs.
I feel you skate over why or how you blew up the op amp chip.. you talk a bit quickly and mention "no input protection"
I think you actually meant to say no output protection (please clarify if not)..
And which port? the GPIO thing is save to load right? a TTL output? safe to short it?
So I'm gathering you can easily blow the ANALOG output on this thing just by turning up the output with a 50 ohm load on it not to mention a something lower such as speaker as a load.
So no output protection whatsoever?
And I take it I shouldn't try to drive anything low impedance on this thing?
If you put a DC short on it will it blow as well?
Again thanks and absolutely no disrespect.. Thanks for taking he time to make the video...
The people selling these things have not taken any such time or care as you have.


Steve

[vladimirsvirid]

rining on oscilloscop may be from coax  ? try dirrect with probe ..
crap generator .
soty for english .

[englishrupe]

Hey i just paid $7.95 for mine....and i am not complaining!

[techobsessed]

For what its worth, I tracked down the origin of this design and linked to it from my own quick review of a similar unit I bought on eBay earlier this year.

[zthetha]

Interesting vid on a gizmo I was about to buy for fun. Don't think I'll bother now. The guy's delivery is probably within the normal range for Yanks but a challenge for English speakers in the UK consisting, as it does, of mumbles, grunts with the occasional unnecessary ejaculation. Still - better than that squeaky, whinging Aussie guy.