Audio decibel level detector with meter driver

[diegofernandove]

Hello, 

I need to make a soudmeter (in dB), reviewing the information I found with the application note AN1991. Now I have any doubts. 

1. For the audio input can I use a microphone of type Electret Condenser ??? (Manufacturer Part Number: POM-2735P-R ). 
2. It is necessary a pre-amplifier stage for the microphone or can you connect it directly to the audio input? 
3. Can the SA604A work in the badwidth of 20 Hz to 20 KHz. 
4. The range of mesurement is between 50 dB to 100 dB.

[ThomasSchloeter]

Sorry to bring up this old topic but I am trying to build a very similar application and after reading AN1991 I am asking myself if there are special requirements to the capacitors used.

I would use tantalum capacitors for power decoupling. Any recommendation for the coupling and decoupling caps in the signal path?

Thanks in advance.

Thomas

[LPP]

Microphone can be connected directly (via a capacitor) to the input of SA604A. External 2.2k resistor to VCC~5V should be used to feed the microphone.

Using pre-amplifier is not mandatory but it can be used to shift the signal level to the working range of the SA604A.

SA604A has been designed for RF operation and it can work in the bandwidth of 20 Hz to 20 KHz.

>The range of measurement is between 50 dB to 100 dB.

Sensitivity of POM-2735P-R is -35dB @ 2.2kOhm. When it is connected directly to the SA604A with input impedance of 1.6kOhm, the final sensitivity of microphone will be -35.7dB.

For SPL range 50..100dB, the SA604A input level will be -79.7..-29.7 dB. This range fits the operating range of the AN1991 circuit: -80..0 dBV.

To measure lower sound levels, use pre-amplifier. Optimum gain is ~29dB to measure sound level range of 20..100dB.

Have a great day,
Pavel
NXP TIC

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[sushruta_p]

Hi,

Could you please elaborate on how SA604A input level values have been arrived at, in the above post.

Regards

Sushruta