So the lesson to learn is to never remove VCC from a chip when you feed voltages to some other pins unless the datasheet for the chip explicitly says that it is ok. Most datasheets tend to say that input pins may not have voltages higher than 0.3V above VCC. 5V on an input and 0V on VCC is way, way, way above that figure.


No measuring circuit is ever error free. The reason why we pay thousands of dollars on instruments is to get instruments where the errors are slightly less than for cheaper instruments.

But the ADC is nothing but an ADC. To measure temperature, you need a temperature sensor. And unless that sensor emits a voltage within the range supported by the ADC, you will need electronics to interface the sensor with the ADC. What sensor do you use, and how have you interfaced it?



You don't. The ADC is nothing but an ADC. It will produce an integer value - a number without unit. It is then up to your software to convert the raw ADC value into a temperature value. If the temperature probe is linear, you will need to multiply with a scaling factor and add a zero-adjust offset. If the probe isn't linear, then you will have to find an equation that converts from the nonlinear value into a linear temperature. Or you will have to perform measures for a large number of temperatures and create a piece-wise lookup table where you perform linear interpolations for the conversion. When you have converted the number from the unit-less ADC value into a temperature, you will have to perform the next step, where you convert the temperature into digits, with - or without - a decimal.

Remember that the decimal is just something virtual. If you have a temperature 10.3C and multiply the value by 10, you will get 103 - a number without a decimal point. So you can perform your calculations with integers, and just remember that the lowest digit of your scaled temperature isn't one-degree steps but 0.1 degree steps. Then it is easy to emit the individual digits to the display.


In some situations, the cheapest solution may be to select a processor with integrated ADC of required specification. A problem is that we don't know about prices and availability of processors or external ADC where you live.