connecting NH3 and Co sensors to PIC16F877A

[amindzo]

Hi,i want to connect ME3-NH3 and ME3-CO gas sensors to PIC16F877A,but their datasheets are not complete and not clear, i have sent a mail to company and they send me some more information but i don't think it's enough, i attach them for you, could you tell me how can i connect them to PIC16F877A(hardware) and how can i write the code?
I use picbasic pro.

if you want more information about these sensors you can see this site:
**broken link removed**

thank you

 

[ericgibbs]

Hi,i want to connect ME3-NH3 and ME3-CO gas sensors to PIC16F877A,but their datasheets are not complete and not clear, i have sent a mail to company and they send me some more information but i don't think it's enough, i attach them for you, could you tell me how can i connect them to PIC16F877A(hardware) and how can i write the code?
I use picbasic pro.

if you want more information about these sensors you can see this site:
**broken link removed**

thank you

hi,
These sensors require Conditioning amplifiers before they can be used with a PIC.

Look at these links,, Application Data.

**broken link removed**

**broken link removed**

**broken link removed**

 

[amindzo]

i saw that circuits but what's the output of that circuits? how can i connect them to PIC16F877A and how can i measure the concentration of the gas with PIC?

 

[amindzo]

Hi, i want to measure the CO and NH3 concentration and when it reaches to warning value then the PIC turn on the alarm and other things, with this application i think i can use MQ7 and MQ137 sensors, i attach you the application circuit of MQ series.
you can see MQ7 and MQ datasheets in this page:
**broken link removed**

i think i should use MQ7 and MQ137 with this application, so i think i should use MQ series application circuit( that i attach you) and i can adjust the warning value with putting a potentiometer instead of red circled resistor in the picture(attached file) and turn it until adjust to warning value . am i right?
but how can i calibrate the sensors in clean air? how can i understand that the value of potentiometer reaches to the suitable value ?

Note: more information in attached files

 

[ericgibbs]

i think i should use MQ7 and MQ137 with this application, so i think i should use MQ series application circuit( that i attach you) and i can adjust the warning value with putting a potentiometer instead of red circled resistor in the picture(attached file) and turn it until adjust to warning value . am i right?
but how can i calibrate the sensors in clean air? how can i understand that the value of potentiometer reaches to the suitable value ?

Note: more information in attached files

hi,
Look at this modified dwg, there is already an adjustment pot in the circuit.
If you require to change the resistor you circled, use a pot.

You will have to calibrate the sensor using a NH3 or CO gas specimen of known concentration. OK.?

EDIT: sorry I had to close down quickly, electrical storm.

Attached the dwg. The output drives a buzzer.

 

[jpanhalt]

Hi, i want to measure the CO and NH3 concentration and when it reaches to warning value then the PIC turn on the alarm and other things,...

Look at Chart 3 (3.2.2) in the link you give in your first post for this thread. I am referring specifically to the relationship of time to sensitivity for ammonia. After about 2 to 3 minutes exposure to ammonia, it appears sensitivity drops to zero. Sensitivity is recovered after the monitor is removed from the gas, but it is uncertain what exactly the recovery time is.

In other words, it appears the sensor you have picked is intended for periodic measurements, not for continuous monitoring. How will that fit into your planned approach to continuously monitor?

John

 

[amindzo]

i want to measure every five or ten minutes

 

[ericgibbs]

i want to measure every five or ten minutes

Did you see my last post with the modified drawing.?

Quote from John.

In other words, it appears the sensor you have picked is intended for periodic measurements, not for continuous monitoring. How will that fit into your planned approach to continuously monitor?

This means you will have to physically remove the sensor from the NO/CO atmosphere between measurements in order to allow the sensor to recover.

In laboratory conditions this is normally done by purging the sensor measurement chamber with clean air after each measurement.

 

[amindzo]

ok, i get it now but you talk about ME-NH3 and ME3-CO or MQ7 and MQ137? the sensors should be always in that environment.

 

[jpanhalt]

I was referring specifically to the ME-NH3 as described in your first post in this thread.

As you stated:

Hi,i want to connect ME3-NH3 and ME3-CO gas sensors to PIC16F877A,but their datasheets are not complete and not clear,...

The earlier time you posted on this subject, you mentioned the MQ137, but its datasheet wasn't available on the link you provided. The new link/datasheet is interesting. It has a built in heater, so may not need to be flushed between samplings.

I am sure others would like to know which sensor exactly you want to design for.

John

 

[amindzo]

you can see MQ137 datasheet on my third post in this page.

 

[smilerG]

Hi, i bought a MQ-7 carbon monoxide sensor from www.futurlec.com and can't figure out how to connect the pins. I already have a datasheet but it gives insufficient information about the application circuits of the sensor.