Re: Knock sensing ideas and circuit designs
Posted: Thu Sep 03, 2009 1:29 pm
Wow 2 mega ohm you say that's up there. Makes sense why they bias microphones I guess.
I'm also certainly not saying we need RF level design. I'm not concerned about SWR, reflected energy or anything like that. What I was trying to stress, is that with a 20K sound card connected to a 2M microphone, an 800 mV signal will be very different than if the to a 2M sound card. It's very likely the maximum energy you can couple from the microphone to the sound card is when the impedances match. Kind of like an 4ohm speaker with an 4ohm amp.
Good to hear the 20K, that's not far off from the 25K min for the TPIC. This means your data should be very close to what we would expect with the TPIC with min resistor installed. I suspect the empirical data will show us that we want the R1 to be around 1M to 2M, with R2 around 100K.
I'm also certainly not saying we need RF level design. I'm not concerned about SWR, reflected energy or anything like that. What I was trying to stress, is that with a 20K sound card connected to a 2M microphone, an 800 mV signal will be very different than if the to a 2M sound card. It's very likely the maximum energy you can couple from the microphone to the sound card is when the impedances match. Kind of like an 4ohm speaker with an 4ohm amp.
Good to hear the 20K, that's not far off from the 25K min for the TPIC. This means your data should be very close to what we would expect with the TPIC with min resistor installed. I suspect the empirical data will show us that we want the R1 to be around 1M to 2M, with R2 around 100K.