Review: Function generator “in the pocket”

Conclusion

This is a handy app for beginners and everyone forever short on space and wanting to carry a versatile audio signal generator in the pocket, for quick deployment. The generator’s dual channel capability and waveform memory should allow less common measurements to be carried out in conjunction with an oscilloscope (whether an app or a ‘real’ one).
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On the down side, the rectangle wave is shoddy and has severe limitations even for simple use, where it may create more problems than help you to resolve. Although supported by an impressive and sleek UI, the rectangle part is probably beaten for cleanness and risetime by just about any generator with more than five electronic parts.
All considered I would heartily recommend the Keuwlsoft Dual Channel Function Generator, bearing in mind its limitations compared to a benchtop instrument. Well deserved, the 4.5 star rating this app got on Play Store. Restricted to the sinewave and the audio range the app is great for educational use, quick testing of audio gear, and exploring acoustics. And of course to bargain for lower prices on your e-debris purchases.

Equipment used

Tektronix 2235 100-MHz oscilloscope; Earphones cable, salvaged; 2 x binding post to BNC adapter; Samsung J5 DUO (2016) smartphone; 2 x 150-ohm resistor.

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About Jan Buiting

Jan Buiting (1958) has been active in electronics and ways of expressing it since the age of 15. Attempts at educating Jan formally have so far yielded an F-class radio amateur license, an MA degree in English, a Tek Guru award, and various certificates in ele... >>

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Discussion (6 comments)

PPihkala 7 years ago

Maybe one should test square wave signal output with other android devices. I think it is possible that different devices use different audio chips and that probably does show in the output. On the other hand it is (or should be) known fact that with 44.1 kHz sample rate one can not reproduce for example 10 kHz square wave. Therefore for HiFi one should use something like 192 kHz sample rate or more.

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n111ckk 7 years ago

I discovered this generator a couple of years ago, and it's superb for audio work. To my astonishment, my HUDL (Android) appears to have a DC coupled output, so even sub-Hz waveforms come out fine. There's all sorts of modulation, chirp, burst modes together with variable duty cycle, and pink and white noise sources.
But the most surprising capability is to produce phase-shifted pairs. These create lissajous figures if your 'scope has an X-Y display function - great fun.
With a stereo power amp and a couple of audio power transformers, one can make a 400Hz 3-phase supply!

Paul Cohen 7 years ago

3-Phase?
HOW?

If you use Excel or similar spreadsheet to create three sine waves 120 degrees apart, then subtract the third from the first, and third from second, you'll get two sine waves 60 degrees apart.
This is equivalent to making one pole of the 3-phase source tied to 0V. So make two equal-amplitude sine waves from the function generator 60 degrees apart, connect the left, right and ground to three equal value resistors and tie all the other ends of the resistors together. Attach your scope ground to this node. The three resistors will have 120-degree apart sines on them (3*60degrees in the delta triangle!). Of course the generator must be floating from the 'scope ground. There's something not quite right on my HUDL tablet regarding phase delay - I have to set 71degrees to get 60: the three phases are different amplitudes otherwise.

For a high power source, amplify the two channels and float using power transformers. Tie one winding start of each transformer secondary together, this will give you a delta supply. To get the star point, you would need a three-phase transformer, 3 single transformers/inductors or power resistors as per the simple experiment above.
Note that any reactive load will be dissipated in the amplifier, which should have clamp diodes to prevent over-volting the output transistors. Unless you can get very low DC offsets on the amplifier, you may need a small series ballast resistor to prevent transformer saturation.

2 Comment(s)

Erkki Koskimo 7 years ago

Absolutely fine support to all of us electronics etc minded and interested.
More this kind of superior application to help and guide hobbyist to more interesting experiments and 'maybe' also in getting to find and realise 'new innovations'!
Very best regards and thankl You.

Erkki
Helsinki
Finland

zohomail service 7 years ago

Dual channel function generator, which has multiple advanced features like touchscreen, Bluetooth, radio, wifi etc. It provides the user a new modernized tech interface.

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