hey hi
can qtr-8a be directly used with 8051 without adc ? if no then which is the best adc that can b used with it.
i have adjusted the sensors 7 mm(.275 inch) above the surface to solve the purpose of a line follower.

Hello, Abhi.

You might be able to get some basic differentiation between light and dark surfaces by connecting the outputs of the QTR-8A to digital inputs, but how well it will work depends on the contrast between the reflectance of the light and dark surfaces. Please note that we recommend a maximum sensing distance of about 6 mm, as stated on the product page. We do not have any particular recommendations for a standalone ADC.

As an alternative, you could consider our QTR-8RC, which can be read without an ADC by timing how long it takes for the output capacitors to discharge.

- Kevin