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PSoC 5, 3 & 1

AlVa_264671
New Contributor II

Hi there !!!!!

   

 

   

I woluld need again your help!

   

I am triyng to read on display module four FSR ( force sensing resistor) and  they look lik NTC thermistor in relation to resistance  versus physic exitation. In this case  exitation is a finger tip touch.

   

I have multiplexed them to a ADC_DelSig_v3_09 and I have used harward multiplexer.

   

I have atacched a bunddled zip with the proyect.

   

The TIA has an output of vdd/2 when any FSR is pressed, and  vout can reach 0 V  depending on the strenght of the touch can be.

   

So the input range of my ADC is 3.3 V/2  to 0v.

   

The result is the four redout are  0x00008104 always , which it seems to be correct when any FSR is pressed.

   

But it does not work when I press any of the FSR.

   

I would apreciate any help

   

Thank you very much.

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8 Replies
Bob_Marlowe
Expert II

You just forgot to wait for the conversion ready with

   

ADC_DelSig_IsEndConversion()

   

Have a look into the datasheet under APIs

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AlVa_264671
New Contributor II

Hi Bob ! thank you for your promptly answer being today Sunday ,. have a good one!!!

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Bob_Marlowe
Expert II

TV-program is rather poor today

   

Hope your project is running now correctly.

   

 

   

Bob

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ETRO_SSN583
Esteemed Contributor

I do not think you need TIA given the resolution of the DelSig.

   

Just terminate the sensors to ground with a sampling R

   

which forms a simple divider. Plus DelSig has an input

   

buffer that you can take G up to 8.

   

 

   

Regards, Dana.

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ETRO_SSN583
Esteemed Contributor

One other thought, you could run DelSig in continuous mode,

   

attach ISR to EOC, throw away a couple of samples and use

   

the next. This would allow CPU to do other stuff instead of sitting

   

in a blocking f() waiting for A/D to finish. Or rewrite code to use

   

end of conversion f() to use non blocking return.

   

 

   

Regards, Dana.

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ETRO_SSN583
Esteemed Contributor

BTW, the conversion G tolerancce of the TIA is awful, another reason

   

to not use it.

   

 

   

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AlVa_264671
New Contributor II

Thank you dana for your sugestion I have replace TIA for other confifuration ( buffer and resistor divider) and  it work Ok !!!

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ETRO_SSN583
Esteemed Contributor

Its importent for you to do an error analysis of the sensor/divider network

   

and the A/D to make sure repeatability is accomplished in your product design

   

and you meet your design goals. Easiest way to do this is convert all errors to

   

LSBs and add them linearly.

   

 

   

Exccept noise related analysis, which has to be done in RMS.

   

 

   

Regards, Dana.

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