Thanks, Ben. I really need to learn more about the AVRs and coding for them in C and ASM; at this point I just kinda splash around in my ugly hybrid of Arduino and C code.

i connected the joystick as you told me to but will 128 to 775 arduino be same for AVR atmega8 ? or will it vary . Because i wrote the code for the same and I am not getting the output at all .

Well, what kind of values are you getting, then? Do you have a way of checking what the actual values are?

well i implemented it using LEDs as output for joystick input but did not get anything . How do i check the joystick output using a multimeter ie should i check the resistance if yes, then what range

No, connect the +5V and GND connections to the joystick, then measure the voltage between GND and the X axis contact or the Y axis contact. It should vary between 0v and 5v.

okay will do that and check whether my connections right or not thank you

Sure thing. And based on the voltage levels that you can see, we can verify what kind of thresholds you'll need for your ADC code.

okay that will be great will do it as soon as possible

Excellent, keep me posted.

I am getting x-axis - 4.32 to 0.74 volts
and y-axis - 4.02 to 1.36 volt how do i interpret this data ?

Well, you can firstly recognize that the joystick is indeed working properly. Secondly, have you read stuff like this guide on using the AtMega8's ADC?

http://avrbeginners.net/architecture/adc/m8_adc_example.html

Particularly: "The recommended ADC clock range is 50 kHz to 200 kHz. If a faster ADC clock is used, the resolution will go down. The ADC clock is prescaled from the main clock by a seperate ADC prescaler. The division factor is selected with the ADPS2..0 bits in ADCSR (see pages 203/204 of the datasheet). At 4 MHz, appropriate values are 32 (resulting ADC clock is 125 kHz) and 64 (resulting ADC clock is 62.5 kHz). We'll use 32."

The ADC has a resolution of 10 bits, which means that the valid values range from 0 (0v) to 1024 (5v). How about if you set a threshold on one of the axes to 512 or so, and just see if you can make an LED light when you push the joystick one way but not the other way?

yes i read the atmega8 datasheet regarding adc thanks alot for the info i figured out how to get the input in decimal and then converted the same to hex . ADC= Vin*1024/ Vref
where Vin is the analog data input and Vref is the internal or external Voltage we use for ADC i am using internal ie 2.56V
and got the dat thank u

That's great! So does that mean that everything is working now?

no i guess my code ain't right then its a pain now . Working past 2 days I hope it works before my final display

You're welcome to post some of your code here if you'd like us to help you proofread it.

Code:

Well, you're just reading ADCH, not the ADCH/ADCL pair. That's a problem.

If you only want an eight-bit result, set ADLAR in ADMUX (ADMUX |= _BV(ADLAR)) and read ADCH only. This "left adjusts" the result (ADCH contains bits ADC9..ADC2), so ADCH contains ADC9..ADC2 as opposed to six empty bits and ADC9..ADC8.

Edit: Though, of course, your code does set ADLAR (I'd recommend using symbols rather than magic numbers). I'm not sure why your code is not working as you'd expect, though it's tricky to say without having the circuit in front of me (I'm not too good at running code in my head).

yes i guess thats what i realized today that i am using only ADCH and not ADCL il write a new code using ADCL and run it again. And i hav done a few mistakes too i have used free running mode and ADSC which does not go hand in hand a realized that a little late . I am reviving the whole code all over again

If you're only interested in an 8-bit value (from 0..255) then set ADLAR (as you currently do) and use ADCH (as you also currently do). If you want the full 10-bit range (0..1023) then reset ADLAR and read ADC.