I am building a "sound level meter". My prototype is based on this circuit at the following web site:
http://digitdiary.co.nr/2010/04/audio-level-meter-circuit-using-lm3915.html
It works fine with a normal audio input, ie, from my mp3 player. I want to make this work with a microphone.
I have an electret microphone and have hooked it up as following: +5V connects to a 1k resistor, and the other end of the 1k resistor connects to the anode of the electret microphone. Then the cathode of the microphone connects to ground. I have used a 1uF capacitor between the microphone anode and the signal input of the LM3915.
The problem:
This only works sometimes. If I turn on the LM3915 circuit without input, ALL of the LEDs are illuminated. Why is this?
If I connect it to the microphone circuit, all LEDs are illuminated as well. HOWEVER, if I first connect my mp3 player, the display works as it should, and THEN disconnect the mp3 player and instead connect the microphone, everything is fine.
I did measure the output of the microphone biasing circuit and the peak output is around 1.5V, similar to the output of the mp3 player.
I am confused as to what is going on. Any insight?
http://digitdiary.co.nr/2010/04/audio-level-meter-circuit-using-lm3915.html
It works fine with a normal audio input, ie, from my mp3 player. I want to make this work with a microphone.
I have an electret microphone and have hooked it up as following: +5V connects to a 1k resistor, and the other end of the 1k resistor connects to the anode of the electret microphone. Then the cathode of the microphone connects to ground. I have used a 1uF capacitor between the microphone anode and the signal input of the LM3915.
The problem:
This only works sometimes. If I turn on the LM3915 circuit without input, ALL of the LEDs are illuminated. Why is this?
If I connect it to the microphone circuit, all LEDs are illuminated as well. HOWEVER, if I first connect my mp3 player, the display works as it should, and THEN disconnect the mp3 player and instead connect the microphone, everything is fine.
I did measure the output of the microphone biasing circuit and the peak output is around 1.5V, similar to the output of the mp3 player.
I am confused as to what is going on. Any insight?