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MSP430F5438


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Hello,

    I am working on a project to design LPG detection system using MSPEXP430F5438 experiment board. My sensor gives 3V output when exposed to air and gives around 5V output when exposed to LPG. My sensor should alarm when output is above 3V. I want to use ADC12 core of MSP430F5438A. I have doubts regarding ADC12 like what should be the reference level, what should be the sampling cycle etc.

   Any help would be appreciated. 

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Maximum input voltage to the ADC is the processor's power supply voltage, and should be 3.3v or less. This means you'll need to divide the voltage output from the sensor appropriately. Possibly a resistor divider:

 /- sensor output 
|
10K resistor
|
+- ADC input
|
10k resistor
|
 \-ground
Then you can use 3.0-3.3 Vcc to the MSP to get the internal 2.5v ADC reference voltage. Any returned sample value above 2457 (decimal) should reflect sensor output above 3v, but you may want to raise that higher in case of noise on the sensor output or power supply fluctuations causing false alarms.
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Just to add when designing voltage dividers use the resistor values pretty high to reduce loading effects and discharging (when sensing battery voltage).. I usually add a 0.1uF cap in parallel to the lower resistor (one whose one end is grounded).. It acts as a good snubber.

 

Hope it helps :)

 

 

 

Sent from my RM-914_im_india_269 using Tapatalk

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