engineerhmm
Newbie level 1
i'm working on a small project with PIC18f4550. i must acquire a sound signal, compress it ( by adpcm ) and then send the data via USB for further treatment...
well actually i'm having a problem in sampling the signal. currently my audio input is from the headphones jack in my laptop... when i run a simple sound, i can measure a maximum of 0.6V on my PIC... (Vref+ and Vref- are Vdd & Vss)
I'm using microchip's library for ADPCM (AN643) the compression encoding functions takes a 16-bit signed number (speech sample, 32767 to -32768) and returns 8-bit number containing the 4-bit ADPCM code.
well what should i do now? should i offset the sample by 2.5V and amplify it? will that work?
and what circuits should i use ? for offsetting and amplifying this signal? and by what ratios?
i'm sampling at a 8Khz frequenct... pic's ADC resolution is 10 bits
well actually i'm having a problem in sampling the signal. currently my audio input is from the headphones jack in my laptop... when i run a simple sound, i can measure a maximum of 0.6V on my PIC... (Vref+ and Vref- are Vdd & Vss)
I'm using microchip's library for ADPCM (AN643) the compression encoding functions takes a 16-bit signed number (speech sample, 32767 to -32768) and returns 8-bit number containing the 4-bit ADPCM code.
well what should i do now? should i offset the sample by 2.5V and amplify it? will that work?
and what circuits should i use ? for offsetting and amplifying this signal? and by what ratios?
i'm sampling at a 8Khz frequenct... pic's ADC resolution is 10 bits
