I have been working on QTouch Implementation for ATmega32 Micro controller. I have taken reference from here. I'm facing issue with grounding Problem. For debugging process I am displaying the result of ADC channel on UART terminal. I have used 125Khz ADC Prescalper and AVCC as REF voltage with 0.1uf cap on AREF pin.
When my ATmega16 is connected to My laptop with AVR USB programer and USB-TTL converter, Result varies from 400-550 on terminal without touch. when touch is perform it goes upto 580-620. I have code to blink LED when it touched (i.e. ADC value goes upto 580+). It blinks when touched an stay off when no touch.
but when I give external supply voltage from an adapter and remove USB programmer and TTL-USB converter, it starts blinking without touch.
When I have measured voltage of VCC in first case (i.e. Without adapter), it is ~4.56V. When I connect external Adapter VCC is ~4.95V.
when I have connected external adapter with the ATmega16 (~4.95 VCC), and USB-TTL for debugging(USB AVR Programmer disconnected). when there is no touch ,ADC Valu goes up to 528. when It touched , ADC value goes to 530+.
I have again code to blink LED when it touched(i.e. ADC value goes up to 531+). it works but when I remove USB-TTL from ATmega16, LED blinks without touching capacitor sensor.
It is grounding issue clearly. but how to get it solved? I have put 1M Rs sense resistor between ATmega ADC0 and Capsense. here is a schematic of circuit I used. here 0.1uf on power rail is not shown but it is exists on board. I have a development board with take 12V and used LM7805 for 5V regulator. I have used 5V 3A supply directly on VCC-GND of Atmega16, though same result. I am not getting where the problem is? I am seeking a direction please throw light on my path.
Wait for Positive response. :) tanks in advance