Pressure Sensor alarm with PIC16F877A to activate the bulb

[jean12]

Hello,there I would like to control a bulb using a sensor alarm connected to a microcontroller 16f877A
I am having problem for gettingthe values from MPX2100 GP Sensor,can you help?
It is giving 1mv for 1KPa I amplifier but I am getting very low values,can you help me to think on this??

Thanks.

 

[pinout]

As the sensor output is only 40mV full scale, what is your amplifier circuit (and A/D input range)?
Also what is the expected pressure you are measuring?

 

[jayanth.devarayanadurga]

Use a 5V rail to rail Op Amp and amplify 42 mV to 5V and feed it to adc.

 

[jean12]

can you give me an example of rail to rail op amp?

 

[jayanth.devarayanadurga]

Search for 5V rail to rail Op Amp in Google. Use Op Amps from LTC or TI. Use Op Amp as Non-Inverting amplifier.

See if this circuit helps.

 

[Venkadesh_M]

Reduce the ADCreference value to 0.5V

 

[jean12]

but the big problem I have is that I don't know the conveniAble formula for reading those ADC from MPX2100GP.Here below is the datasheetcatalog,can you help me to extract the useful formula for the conversion?

Thanks.
https://biakom.com/pdf/MPX2100.pdf

Thanks

 

[jayanth.devarayanadurga]

What formula. The device o/p is linear.

 

[pinout]

Have a look at AN1315 and AN1324 on the Freescale website
**broken link removed**
just search for MPX2100 if its not there by default or the app note numbers. There's lot more as well.

 

[mithun mohan]

Hi jean12,

I guess this would be the calculation to get the pressure ..

Pressure = ((full scale capacity / excitation voltage) * (measured voltage/caliberation factor))

datas i gathered from the sensor datasheet :-

full scale capacity = 100 kpa
excitation voltage = 10 v
measured voltage = output from the sensor
caliberation factor = .4mv

kpa to bar constant = .01

apply these values to the equation and multipy the final result with .01 to get the pressure in BAR

 

[jean12]

How may I get the pressure in Pa,and also the problem is that I am not able to get the recommended components in the post above #5;I am using an ordinary amplifier TL084 for amplifying the sensor output;can this be helpful for getting the required measurement?

Thanks.

 

[Venkadesh_M]

How may I get the pressure in Pa,and also the problem is that I am not able to get the recommended components in the post above #5;I am using an ordinary amplifier TL084 for amplifying the sensor output;can this be helpful for getting the required measurement?

Thanks.

How many ADC channels you are using and what about the pin connections in Port E and A..

 

[jean12]

I am using channel (0) other ports (PORT E and PORT A ) are not connected except that pin AN0 used as analog input for reading the voltage.

 

[Venkadesh_M]

you can use ADCON1 register and select the mode as only one analog input and +Vref as your choice and by giving the 0.6V to +Vref pin (A diode Voltage) you can make it to increase the resolution...

If you having any way to measure the real presser then calibrate your ADC readings with the real value..........

 

[jean12]

the problem is not conversion of analog data read from the pin but those data to input.

Thanks

 

[pinout]

Hi Jean12,
I think that having received many responses it would now help by clearly restating the problem with examples of the type of detail you require to get the best feedback.

There have been examples of the signal interface, suggested gain stages to match to the A/D, setting the A/D and reference setting, equations to convert the signal to a pressure, my own links to a complete AN design.... so expanding your statement "but those data to input" will help you get the best answers.
Please take this post as intended as it is suggested with best intentions for you to get the best answers.

 

[Venkadesh_M]

the problem is not conversion of analog data read from the pin but those data to input.

Thanks

If you give correct ref value then you can give whatever the sensor input directly unless it was AC..

 

[jean12]

I am powering the circuit with DC source of 10V but the output of the sensor is differential so can this be connected immediately to the PIC?I f yes which voltage to connect,-V or +V?
If not how may I proceed because I amusing a TL084 for making an instrumentation amplifier but it is not giving good results because I have the initial voltage and final voltage and the initial voltage is not fixed,how may I determine the good output.

Thanks

 

[jean12]

What is the output voltage to be considered because normally,this MPX2100 output a differential voltage -V and +V so what is the value to consider?
Now it is giving 3.856V on 2 and 4 pin of it.
Thanks

 

[mithun mohan]

Now it is giving 3.856V on 2 and 4 pin of it

The output voltage you must measure like v+ wrt v- .Did you do that way ?