I'm just curious, but what do you do after detecting a bat?

 

I'm just curious, but what do you do after detecting a bat?

Honestly, I didn't have a plan for post-bat detection. Just thought it would be a fun project to try to hear what my cat hears.

 

I disagree with the Texas Instruments electret mic preamp article:
1) 2V mic operating voltage. Then it distorts with loud sounds.
2) Feeding all the power supply noise directly to the mic biasing resistor with no filtering.

From a 9V filtered battery, I use a series 1k filtered resistor to feed a series 10k current-limiting resistor powering the mic.
If the mic draws its max of 0.5mA then the 11k worth of series resistors use 5.5V and the mic gets 3.5V.
If the mic draws 0.35mA then the resistors use 3.85V and the mic gets 5.15V.

 

I disagree with the Texas Instruments electret mic preamp article:
1) 2V mic operating voltage. Then it distorts with loud sounds.
2) Feeding all the power supply noise directly to the mic biasing resistor with no filtering.

From a 9V filtered battery, I use a series 1k filtered resistor to feed a series 10k current-limiting resistor powering the mic.
If the mic draws its max of 0.5mA then the 11k worth of series resistors use 5.5V and the mic gets 3.5V.
If the mic draws 0.35mA then the resistors use 3.85V and the mic gets 5.15V.

Hi Audioguru.

I like your approach, think it makes sense. Will try that first.

Thanks,

Neko

 

https://www.researchgate.net/profil...ng-Simple-Modes.pdf?origin=publication_detail

Sample Isolated Electret Microphone Frequency Response Curves Compared to ¼" B&K 4939 Style Microphone:

 

Most electret mics have the same specs. Here is the very flat and smooth frequency response of an older electret mic:

 

https://www.researchgate.net/profil...ng-Simple-Modes.pdf?origin=publication_detail

Sample Isolated Electret Microphone Frequency Response Curves Compared to ¼" B&K 4939 Style Microphone:
View attachment 250734View attachment 250747

Hi Danko,

The chart you posted from the ResearchGate paper is interesting. It definitely shows that these inexpensive electret microphones can work in the bat detector. Low noise amplification and good power supply bypassing are still needed, however, but there is usable sensitivity in these microphones.

One contributor made a comment about wind noise that I think is relevant; I'll have see how that plays out.

Thanks,

Neko

 

Hi All.

I'm going to be prototyping soon after ordering some more electret mics. My DSO has a FFT function but I'm thinking that a spectrum analyzer might be better to evaluate the spectral content of the returned bat echos.

There are the standard options for RF use, new and used. Since I'm not in the RF world anymore, I don't need a DC- white light analyzer but could work with either small stand-alone unit or a PC based modular unit both with bandwidth capability for this project and more. A tracking generator would be nice but not necessary.

I wasn't sure how the spectrograms in an earlier post in this thread were produced:

http://users.telenet.be/airborne/Bats_in_the_garden.htm

Any suggestions are welcome and encouraged.

Thanks,

Neko

 

I was also going to build a bat detector until about 10 years ago my city put larvicide in all the ponds and drains to kill mosquitoes.
Now all the mosquitoes and all the bats that ate them are gone.

Today, instead of heterodyning bat sounds down to my hearing sounds I directly listen to cardinal birds singing their mate-attracting songs.