The time constant(sec) of an RC circuit is equal to the product of the resistance and the capacitance of the circuit.

It is the time required to charge the capacitor through the resistor to 63. 2% of full charge,or to discharge it to 36.8% of its initial voltage.

The voltage of the RC circuit is measured using adc of the ATmega8, input voltage for RC circuit is given from PB0. The timer is started at the time of the PB0 making 1 .

The adc of ATmega8(ADCH) is 8 bit long so corresponding to 5V get 255 in ADCH. The TCNT1 value is taken to a variable when the output voltage of the RC circuit become 63.2% of the input voltage.That is 3.16 v corresponding to these voltage ADCH show 161(appr).

Using an LCD can show the TCNT1 value. TCNT1 is 16 bit long.Here ATmega8 running in 8MHz clock,timer prescaled by 1024.

So if you get the real time multiply the TCNT1 value to (1024/8000000).

Some test examples:

AVR microcontrollers are a popular choice for use in a wide range of applications, including embedded systems, robotics, and more. They are known for their low cost, versatility, and efficient use of resources, which make them an attractive choice for many developers. If you are working with AVR chips, you will need a programmer to burn programs onto them. One option for an AVR programmer is the USBtinyISP, which is a simple and low cost solution based on the attiny2313 microcontroller.

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package required in linux

binutils: Programs to manipulate binary and object files that may have been created for Atmel’s AVR architecture. This package is primarily for AVR developers and cross-compilers.

gcc-avr: The GNU C compiler, a fairly portable optimising compiler that supports multiple languages. This package includes C language support.

avr-libc: Standard library used for developing C programs for Atmel AVR microcontrollers. This package contains static libraries, as well as needed header files.

sample programme to blink a LED.