Design signal input for an Sound Level Meter

[ryeeson]

i'm newbie.

what thing i must consider and understand to design an input signal circuit for an Sound Level Meter with LM3915?
let say if i connect the pc microphone directly to the input of LM3915(pin 5), there is nothing happend. what i intend to do is when the microphone pick a noise, then the Sound Level Meter(SLM) should light up the LED according to the noise.

 

[rkodaira]

Hi !

You should consider using an Operational Amplifier to match the impedance and amplify the noise signal to levels acceptable to the LM3915. After the amplification, you can also rectify the signal (as the LM3915 works with positive voltages in its input). Take care about the signal bandwidth to be measured, and another option is to filter the noise to measure it only in determined frequencies or band.

 

[ryeeson]

wwhat do u mean by "to match the impedance"?

what is the "levels acceptable to the LM3915"?

so i already read the data sheet of the LM3915. can i just take the rectifier in the data sheet of the LM3915? full wave or half wave? what the peck-to-pack detector for? do i need them?

What is the signal bandwaith to be measure? i want to measure from 0dB to 70dB.

Thanx.. but ireally need ur help