ADC0808

[ajayshankar]

Hello everybody,
i am using ADC0808,in which i am using only 3 channels for temperature, humidity & wind direction sensors.But whenever i am removing any one the sensors, the other two sensors are giving garbage values.So what is problem.


Ajay

 

[Nigel Goodwin]

Hello everybody,
i am using ADC0808,in which i am using only 3 channels for temperature, humidity & wind direction sensors.But whenever i am removing any one the sensors, the other two sensors are giving garbage values.So what is problem.

You shouldn't let the inputs float, it's likely to give wild readings. It could well be affecting the others because you're not allowing enough settling time between readings - in which case the previous readings may well have been inaccurate as well!.

I presume the ADC0808 has internal sample and hold?, if so, just like a PIC A2D, it takes time for it to change when you switch channels - if you read it before it's settled you won't get the true reading, but one between the correct one and the last one you read (as the capacitor charge in the sample and hold changes).