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Topic: not getting an analog reading from my gas sensor (Read 392 times) previous topic - next topic

encryptor

I'm trying the following project however I'm not getting an analog reading from my gas sensor.  

http://nootropicdesign.com/projectlab/2010/09/17/arduino-breathalyzer/comment-page-1/#comment-735

Can the 2 GND's after the voltage regulator be connected to GND on Ardunio board?
Or do I connect these 2 GRD's to the GRD pin of voltage regulator? Thanks.
peace*&^

encryptor

First I connect the battery terminals to the (+/-) power strip rows along the side of my breadboard.  Then I connect the voltage regulator and get the readings I would expect.  However, when I connect the sensor's and resistor's GND to the (-) power strip row in addition, then my readings for the voltage regulator drops significantly.  Tying the 2 extra GND's to (-) power strip row weakens my circuit.  Why is that?  What should I do?
peace*&^

retrolefty

The grounds on the voltage regulator, the gas sensor and the end of the 10k resistor must all be wired together and then wired to one of the arduino ground pins.

Lefty

encryptor

#3
Nov 12, 2012, 08:57 pm Last Edit: Nov 12, 2012, 09:13 pm by encryptor Reason: 1
Is it correct to say that the (-) neg terminal of the 9V battery and all GNDs of circuit get tied together to a GND pin on the Ardunio board?  If so, then the 9V battery is not enough voltage to output 5V thru the voltage regulator.  Why does the voltage decrease across the voltage regulator when I attached the sensor's and resistor's GND to (-) neg terminal of the 9V battery?
peace*&^

retrolefty


Is it correct to say that the (-) neg terminal of the 9V battery and all GNDs of circuit get tied together to a GND pin on the Ardunio board?  If so, then the 9V battery is not enough voltage to output 5V thru the voltage regulator.  Why does the voltage decrease across the voltage regulator when I attached the sensor's and resistor's GND to (-) neg terminal of the 9V battery?


Yes, all those ground connections must to made.
Perhaps your gas sensor's current draw requirement is more then a small 9vdc battery can supply. Such a battery type is a very poor choice for most useful arduino projects. If you attempt to draw too much current from such a battery it's terminal voltage will decrease from it's nominal value perhaps below the minimum drop out voltage input voltage rating for the 5vdc voltage regulator. Do you have a link to a datasheet for the gas sensor from the original manufacturer?

Lefty

retrolefty

OK, I found this datasheet at sparkfun:

http://www.sparkfun.com/datasheets/Sensors/MQ-3.pdf

This sensor needs/has an internal heater of 33 ohms so the current draw for the sensor is at least 150ma which in my opinion is way to much for a standard small 9vdc battery. You are going to have to find a voltage source with better current capacity.

Lefty


encryptor

You are totally right!  Thanks for the help! 8) +1 karma for you!
peace*&^

encryptor

#7
Nov 12, 2012, 10:29 pm Last Edit: Nov 12, 2012, 10:30 pm by encryptor Reason: 1
Even though I can agree with your answer I see on Wikipedia that my Zinc Chloride (zinc carbon) battery has a typical 400 MAh rating.  That would make me think 150mA isn't all that much to draw from a 9V battery.

http://en.wikipedia.org/wiki/Nine-volt_battery
peace*&^

retrolefty


Even though I can agree with your answer I see on Wikipedia that my Zinc Chloride (zinc carbon) battery has a typical 400 MAh rating.  That would make me think 150mA isn't all that much to draw from a 9V battery.

http://en.wikipedia.org/wiki/Nine-volt_battery


You need to find out at what continuous current draw that 400 mah rating is given at. Mah ratings can be quite deceiving, they are more a marketing specification rather then a good technical specification. You need a stronger voltage source, that is the bottom line. If your 5vdc voltage regulator is not putting out +5 volts powering the sensor then the battery voltage is dropping under the load.

Lefty

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