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ebay eval board AD8221AR-Precision-Instrumentation-Amplifier-Module testing


Got two of these small amplifier carrier boards to play with.


There are may of them available. No information, circuit diagram or anything ....other than picture. Spec is the op.amp. not the circuit.

However, the circuit is simple to track and pins are clearly marked.

It is pretty much like RF-rejection circuit from the data sheet or this one:

Excluding common input capacitor (no C2) and only single bypass capacitors on power lines. RG is 499R i.e. G=100.

Input filter is on pretty low frequency.

Thinking of removing filtering capacitors and RG. Would like to test it without filtering and G=1 to see actual income on nominal max. frequency.

It always amazes me how much of this stuff is sold with zero technical details. Obviously the seller is just a box shifter, but would sell vastly more if they included basic information!

Well, those must be surplus from some sensor or something else, this would make sense.

Can'r really think why someone would produce large quantity of aplication book circuit for sale and then provide zero information to hamper the sales.

What pisses me off that even when there is a end product, chinese have tendency to provide IC spesification values as a board spesification...which is plain lie.

Like here gain is set with a single reistor. When gain is set it affects whole lot of other charracters. Another question is RF-rejection filtering. With chosen input low pass filter values and gain on 100  -3dB bandwidth is closer to 1 kHz than the "advertised" 825 kHz, 3 dB bandwidth (G = 1) of the instrument amplifier IC.

Which is even more critical are sepper mor drives, their spec should be fairly straightforward to advertise, but all sellers have chosen to use driver IC absolute maximum rating or other non aplicablee values.

Like this
TB6600 4A CNC 32 Segments 42V 42/57/86 Stepper Motor Driver Controller

Guess what?
* It does not have TB6600 chip, but smaller TB67S109AFTG
* Spesification is for TB6600 chip, if you try it on those either chip will fry
* The TB67S109AFTG chip PCB/cooling is designed wrong, chip is wrong side of the PCB, it is designed to cool trough the PCB not from the isulating plastic back....where is piece of loose aluminium laced with a suposedly thermally conducting pad (or tape).

Got on and it did not worked. I got money back, but not happy using thee evenening to get it work when I figured it would never produce even half of advertised current. I was not happy with that.

But I am happy with this little amplifier, even when it had pretty much no information. But it's simple circuit and PCB form factor works just fine for breadbord prototyping.

I have no ways (yet) to design and make that small PCB's, happy I got something to play with and test.


Unsoldered two very small filtering capasitors off. Now 20kHz comes trough clean at G100.

Somewhere 50-60kHz sinusoidal input signal turns to triangle wave.

On first picture the two small blobs are removed capasitors. 1/8w resistor is for scale only.

Removed the RG-resistor to set amplification to 1. This will allow me to check input/output range at diferent frequences. Whole to faster with the boar than trying to understand all that information on datasheet. It is all there, but there is so much details and stuff I should remember or have learnt that it could be notes or isobar diagram.

The circuit board starts to look a bit clapped after few iterations.



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