Internal Signal Test for Ganglion

Xp0Xp0
edited December 2017 in Ganglion
Is there some form of internal signal test within the ganglion that can be viewed as output
example: pre-determined 60Hz signal

OR

Is it possible to output a specific signal using the input of a waveform generator with the board? 

Comments

  • I pretty sure you can tie all the inputs to ground to get a measure of the internal noise of the board. Not sure about specs for function generator, but just keep the current low im sure.
  • Hi Xp0,

    Here's what seems right to me ...
    I'll pretend you're only going to use channel 1 ... and you have its input switch position so that 1_IN- is used, not REF, if you know what I mean.

    For just "voltage noise", connect 1_IN+, 1_IN-, and D_G to one node that I'll call "COM".  That's it.

    Or maybe you want to include noise that can result from electrode impedances.  (Some of that could be noise coming from the electromagnetic environment, but some of it could in theory ... I doubt it will in practice ... be due to current-variation coming from Ganglion, running thru the impedances to generate a voltage).  For that, you'll have to decide what's a good circuit model for an electrode.  For surface ECG, what's commonly used for noise measurements, and is (last I knew) in most/all national/international ECG performance Standards, is a 51K resistor in parallel with a .047uF capacitor -- even though it sure depends on skin and the electrode-type, of which there are many.  So you would have that parallel combination between 1_IN+ and COM, and another between 1_IN- and COM, and another between D_G and COM.  

    But I'm thinking you're more interested in a basic signal than in noise?  Try something like this.
    Connect together:  D_G, 1_IN-, leg#1 of a 10 Ohm resistor, and a function generator output's negative-side.  
    And connect together:  1_IN+, leg#2 of the 10 Ohm resistor, and leg#1 of a 100K resistor.
    And connect together:  leg#2 of the 100K resistor, and the function generator output's positive-side.
    That's all.
    Set the function generator for 1 volt peak-to-peak at your favorite frequency.  :)   
    Drawing it out might help, but you might see that what the resistors are doing is dividing the generator output by 10,000, and that divided voltage is between the + and - inputs.  So you can use different resistances and function generator settings if you want different output voltages.

    Something to keep in mind if you were going to connect any other instrumentation to Ganglion during that time.  Many function generators internally connect their output's negative-side to earth ground, by way of the power cord.  Same thing with oscilloscopes/probes, for example.  Don't connect anything like the scope probe ground, to Ganglion's GNDA or anywhere else unless you've analyzed it carefully.

    About D_G.  If you look at a schematic ...
    For some designs, a D_G would be critical, to supply "bias currents" to the instrumentation amp U2.  But with Ganglion I think the 330K "pullup" resistors R2 and R3 should be able to accomplish that, so I'm doubtful that D_G is even necessary for this bench test.  With a patient, when there are electrode impedances, I can more easily imagine some benefit but I'm still doubtful.  If anyone has theory or experimental input about whether or not D_G is needed, and ideally why, I'm pretty curious.

    Hope that works!  Let us know.

        -- Bruce P.

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