Pure tone Audiometer

[Naveen G Bhat]

Dear forum,

While searching reference circuitry for pure tone audiometer i had found one more circuit in which they used micro controller GPIO pins to generate the different frequency levels,i will be attaching that image also please go through once, here i have doubt that how he created the different frequency level by connecting switches to GPIO pins. and how the volume controls are working in attached file.
Do we get frequency signal in all GPIO pins micro controller?? if yes how to get difference frequency level.... what modification i need to do get these frequency ranges??

[Naveen G Bhat]

Thank you sir,

[Paul van Avesaath]

i have no clue, but google is you friend

[Naveen G Bhat]

Dear forum,
I wanted make a pure tone audiometer, i don't know much about it.
if some one knows about pure tone audiometer can some one please tell me that how it works? and what all it includes while designing the pure tone audiometer?.