I am looking for a sensor whose output depends on the 'loudness' of the surroundings. Is this a common cheap sensor or will I need something specialized. I would like to be able to tune the spot at where the sensor triggers, or an analogue solution would work.

Thanks.

 

this sensor you refer to is called a microphone, specifically a directional microphone.... if the output was connected to say an op-amp, you would have an "analog" solution....

 

OK thanks. I'm a little confused on the output of the microphone. Is it indeed going to be higher based on the input to the microphone? I see the response curve is typically flat with respect to frequency so thus for a louder input to the microphone I have a greater voltage out?

Frequency range isn't really an issue and I don't think sensitivity will be either so is there anything else I really need to keep in mind when selecting one? And btw, what is the difference between a uni and omnidirectional microphone?

Thanks.

 

the IC 741 will help you for this

 

OK thanks. I'm a little confused on the output of the microphone. Is it indeed going to be higher based on the input to the microphone? I see the response curve is typically flat with respect to frequency so thus for a louder input to the microphone I have a greater voltage out?

Frequency range isn't really an issue and I don't think sensitivity will be either so is there anything else I really need to keep in mind when selecting one? And btw, what is the difference between a uni and omnidirectional microphone?

Thanks.

what is the difference between a uni and omnidirectional microphone?
uni is one & omni is all direction

 

if you use a 741 many on the forum will tell you it is old and out a date.........
but yes use an op amp. You may want to use a rectifying version of an op amp circuit.

 

Ok thanks all. I've got some lm741's handy so I can play around with these to start.

What sort of amplitude should I expect out of the microphone? I am going to get a very low signal which is why I will need to amplify with the 741 or something similar?

Thanks.

 

An electret microphone is common, inexpensive and works very well. it needs a resistor to power it. If you talk in a normal voice level 10cm away from it then its output voltage averages 5mV to 10mV.

A lousy old 741 opamp is too noisy and has a poor frequency response for audio. Use a TL071 low noise and wide bandwidth audio opamp instead. It is inexpensive.
Then use an LM3915 bar graph driver IC driving 10 LEDs to show the sound levels.

 

Thanks. Will these also be able to detect louder sounds, from further away? I am using it more for noise detection at higher levels.

I will look into the 071 op-amp. This will then be fed into the MCU to do some manipulating with.

I appreciate the help.

 

If you get a TL072, you have 2 opamp sections...you could run the signal into the 1st, amplify it, and then run it into the second section. Gain multiplies, so if the first one was set for gain of 100, and the second 50, you'd amplify the signal by 5,000 times!!! Not that you need to go that high, bc. noise will also amplify too. Make the gain adjustable with trim pots on the return of each opamp (the output to input connection).

The bargraph driver IC is a good idea, above. You could also use an analog meter (needle movement) to show the sound level for simplicity.
Here is some info on the electret mic: http://www.epanorama.net/circuits/microphone_powering.html#basic

Good luck!

 

Much appreciated again. Thanks all.