Hi,
Regarding your application , divide the program in steps.
1. Make a program to interface ADC0804 & LCD
2. Give output of ultrasonic distance to analog input of ADC0804 and displayed digital value on LCD
3. Note down digital values for ur required benchmarks like 3 cm= Value A, 5 cm= Value B etc.
4. In program compare the obtaine ddigital value and drive ur devices accordingly
All the best.
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