Hi all,
I am using the ADC0820 on an 8051 for temperature sensing on an 8051 microcontroller (the Atmel 89C51RB2 to be exact). I only require 5-bit resolution though, but the ADC0820 is an 8-bit converter. Can I use only the 5 LSB pins on the ADC and ignore the other 3 or do I have to use all 8?
Hi,
It is true that by throwing away the three LSBs, your precision of measurement gets reduced from 1/256 to 1/32. But by asking for a 5bit resolution you are OK with it.
Now let us consider the issue of why 5MSBs and not 5 LSBs. Let us consider a 10bit AD converter with a full scale value of 10Volts. The weightage of the MSB in this case will half the full scale=5V. So if you apply 5V to this ADC, the MSB will be set and all other bits will be zero. Now if you throw away the MS three bits, you will get the answer as Zero. If you take five MS bits, you will still get the correct answer. But because you have thrown away three LSBs, your digital value will change next only when the input changes by 1/32 of full scale 10V = 0.3V approx.
Regards, Laktronics