$10 Function Generator - Comments?

Johnny2Bad

Member
2010-05-04 7:51 pm
So I'm performing one of my periodical eBay (and 'net) searches for some of the tools on my list to complete the bench, and I do one with the terms "function generator" (without quotes).

Up comes this Hong Kong based seller with a $US 9.96 / Free Shipping Function Generator Kit (the buyer is expected to "weld" the components onto the board and assemble the device into a plexi enclosure).

Now, I understand that $10 for something that isn't truly usable is still $10 wasted no matter how much of a bargain the purchase is or seems to be. The numbers ... aside from being suspect as a matter of principle when it comes to these types of People's Republic of China (PRC) sourced devices ... are not drool-worthy by any stretch of the imagination, but I'm wondering if anyone feels there are useful applications for a sine wave generator with 1% THD?

And remember ...
" ...
1.After completion of welding on IC, XR2206, pay attention to the direction of IC, insert the might damage the chip!
..."

Comments?

XR2206 Function Signal Generator DIY Kit Sine Triangle Square Output 1Hz 1MHz | eBay

eBay item # 171999013818
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
It is what it is. Something like that was diy state of the art 30+ yrs ago as function generator chips such as the Intersil 8038 appeared.

The chip basically generates a triangular wave, the sine wave is synthesized from that using a diode matrix. That's why the distortion figures are poor.

A CD player and test tones created using Audacity and burned to disc are far lower in distortion but can't go over 20kHz.
 

Mark Johnson

Member
Paid Member
2011-05-27 3:27 pm
Silicon Valley
I bought one. It works okay. I wanted it because it can be operated as a battery powered function generator. So it can be used in floating (non grounded) applications if that's what I want. Because it's battery powered it is perfect for use as a tone generator when beeping out a bunch of in-wall or in-ceiling speaker wires. Clip it onto a wire pair and let it dangle while you hunt for the other end.
 
As to your bench, you can certainly build little kits like this, plus the housings and power supplies they need. But really you can find perfectly usable whole piece of test gear for very low prices in many places, even ebay.

A quick look right now found this for $27

Vintage Heathkit IG 72 Audio Generator | eBay

I have two of them myself, and the work just fine. And nothing to build, they are stand alone units.

More Heath items:
Heathkit IG: Test Equipment | eBay

The IG-5218 is a highly respected piece even in professional shops.

And of course there are plenty of old classic HP signal generators to be had, as well as other hobbyist lines like Eico.

HP on ebay:
HP Oscillator | eBay


And look up your local amateur radio crowd, they often have swap meets and you can find working test gear dirt cheap.


My local university - Michigan State - has a happening surplus facility. They sell everything the Univ wants to get rid of. I have over the years collected a lot of good old test gear, as it was removed or updated from various labs on campus. My $5 HP 200C had only one bent plate on the tuning cap to straighten before it worked like a charm. ANy local colleges near you may have similar facilities.
 
Johnny!

Such a function generator can be used for many purposes. Even distortion metering is possible with some addition and with some limitation. If bandwidth of the measured device is high enough, then you can substract the already distorted input signal from the normalised output signal, this way most distortion originated from generator can be cancelled. [...] Distortion measurement down to 0.01 % is possible.

The most important factor is stability, easy and precise setting. You can compensate or account any error as long as the signal is stable.
 
Hi Johnny, since you are building your own bench, why not get your hands on a used function generator?

There are good electronic test equipment rentals that let rent, lease or buy second-hand function generators. Check these out for instance - https://www.trs-rentelco.com/subcategory/Arbitrary_Waveform_Function_Generators.aspx

The prices are fair; they are known to vouch for their quality - and I’m talking Tek, Keysight waveform function generators- you get to use some of the most reputed brands around. And if stability and precise settings are important to you, you definitely need to invest in reliable test equipment that will last long and won't give you trouble.

All the best!