the best way to measure a resistor of smoke sensor

[stst9187]

Posted on January 17, 2013 at 10:41

What is the best way to measure a resistor of smoke sensor with the  STM32F100 microcontroller?

thanks

[trevor23]

Posted on January 17, 2013 at 10:56

To measure resistance one simple method is to make a potential divider using a fixed resistor and the resistor to be measured. The output of the potential divider is fed into the ADC on the STM32F100. The potential divider supply voltage should be as accurate and stable as possible e.g. use same analog reference voltage as used for Vanalog ref. Depending on the resistor values and the required precision the potential divider input and output might need buffering (e.g. with op-amps). The result will not be linear but can be ''converted'' in software to whatever units you need either by equation or by look up table.

[lowpowermcu]

Posted on January 17, 2013 at 11:28

Hi Treveor,

Perhaps it is better to use STM32F30x family with build-in ADC, opamps and DSP capability.

[stst9187]

Posted on January 17, 2013 at 11:42

thanks, 

The application is low cost.is it better take reference voltage internal or external ?There are some application note about this?Is it possible do a ratiometric measure ?thanks

[trevor23]

Posted on January 17, 2013 at 12:24

Yes, radiometric measurement is possible if you add the associated hardware (would have been good to mention this in your original question). There is nothing specific to STM32 about this - google is your friend.

From experience of the STM32F1 range the internal reference is not very good so I've always used an external reference but I can't say if internal ref is good enough for your application. The buffering requirements for your application are easy to work out from the input impedance figures of the ADC - I always tend to buffer the signal into the ADC unless I know the source has a very low output impedance.

[stst9187]

Posted on January 17, 2013 at 14:34

thanks for all, Trevor