Sound amplitude meter

I made this project as a test to improve a technic to read analog values without analog-to-digital converter. (ADC) I ended with this `sound meter`. It may not work perfectly, it needs some improvement but works anyway. It have the feature of `auto-calibration`, so it detects the signal, amplify it and measures it. Because the `auto-calibration` feature, it doesn't need an amplifier or any aditional circuit to drive the signal from the electret microphone. The capacitor can be a 103k or a 220k. A poliester capacitor works better. The code is compatible con 16F84A or 16F628 so I can't define exactly what value should have. Anyway, If you find this projects interesting, you may be able to experiment with the value of the capacitor.
Sound amplitude meter - schematic

The config should be: INTERNAL RC and PWRT ON for 16F628. For the 16F84A the config is External RC and PWRT ON. As I mention before, the reason of this project is becuse i'm working in a technic to read analog values directly from a signal without an ADC. Here is the method used to read analog values with a digital input output pin: 1. Connect a RC circuit to a Digital I/O pin. 2. Set the pin as OUTPUT and make it high for 1 ms (one milisecond) 3. Set the pin as INPUT and start a 16 bit counter until the input signal is low. The value of the 16-bit counter should be the value of the input signal or the value of the RC. You can learn more about this technic at the Microchip's web page ( reading the application notes at the documentation section.

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