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Help me design a data acquisition circuit for gas sensor array

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hi all,
I am trying to build a gas sensor array [CO, CO2, NH3]... i do not want to connect them all seperately to the microcontroller [using PIC16f866] as i need many port pins for further application circuits... can u plz help me in designing a data acq circuit for the sensor array... am planning to use MQ series gas sensors...

sensor1----> sample and hold1---> MUX
sensor2----> sample and hold2 ----> MUX
sensor3----> sample and hold3----->MUX

from MUX----> ADC of PIC micrcontroller...

can u guide me?
i suppose that i need an external sample and hold ciruit, right?
 

gas sensor array

I am not sure you need the sample & hold. What is the output of the gas sensor? If it is simple a DC signal level then you would just sample it with the PIC ADC S/H.

Keith.
 

Re: gas sensor array

keith1200rs said:
I am not sure you need the sample & hold.
Click to expand...
I concur with Keith. I don't see why you would need an individual sample & hold for each sensor. Gas concentrations change slowly, compared to the rate at which you can scan through sensor outputs with PIC.

CD4051 is a popular analog mux. ADG728 is another good one.
 

Re: gas sensor array

Thank u so much 4 the reply...
My prof wants me to use an external circuit... I will have to perform all signal conditional processes outside the controller...
 

gas sensor array

My pin calculation is this:
- external MUX needs 1 analog input and two digital outputs to control the MUX
- internal MUX needs three analog inputs
What's the adavantage of using an external MUX?

Regarding external signal condition: What do you intend to do?
 

Re: gas sensor array

hi,
am also quite unsure as why he aked me to use external components... ll ask him again about it...
1) i also hav a doubt... since the output of the gas sensor will depend purely on the atmospheric conditons, the input values to my s/h circuit will be discrete (output of the gas sensors will be discrete values!) so wat will be the sampling rate?
2) also can i get any good e-books for better understanding of their practical applications? thanking you in advance...
 

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