sensor interface to the adc port of micro

[chethankp]

Interfacing analog sensor to the micro adc port
Hi,
I have got a new soil temperature sensor (THERM200)from vegetronix.

I tried to interface this to the micro controller's adc port (8051), but it changes the volatge at the adc port when i conect this sensor ,.
first I have verifed adc by providing some extrenal analog voltage , it was giving coorect i.e adc conversion was correct . Here I have checked the volatge of ADC pin with oyt connecting any sensors, its gives 3.3v.


THERM200 sensor outputs from 0 to 2.4v, and
at normal temperature it gives 1.5v , when i connect to the micro it was giving 3.1v at i/p of adc port so adc convertion is also 3.1.
Here link for the above sensor
Soil Temperature Sensor Probes ..

pls help.
regards
chethan

why this is sensor changing that volatge?

 

[nikhil_jain]

which 8051 controller r u using? nd r u using an external adc? pls see that you have the ground common for sensor as well as the controller.

 

[bogusmeister]

hi. are you really required to use 8051?. because ive tried to interface analog sensors with a PIC microcontroller that has an internal ADC(PIC16F877A). and had no problems with it. if you're interested i could give the schematic as well as the codes that i found through the internet..

 

[ckshivaram]

internal or external does not matter here.... see the sensor outputvoltage scale and operating voltage rating.. maybe the sensor is loading the port pin... take care not to damage ADC