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Author Topic: Help on MQ-7 CO Gas Sensor  (Read 1789 times)
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Hi,
I'm new to Arduino. I hope someone can help me with this.

For the MQ7 CO Gas sensor to work, it requires a 1.4V for 60 seconds and 5V for 90 seconds.

Im guessing I have to use PWM. correct me if im wrong but how to obtain such a specific level of 1.4V and 5v?

Pls point me in the right direction guys. Thanks
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The data sheet is as follows: ''http://www.sgbotic.com/products/datasheets/sensors/MQ-7.pdf''
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If you have an Arduino that operates at 5V, the 5V is pretty simple. Turn the pin full on (100% duty cycle).

The 1.4V is not much more difficult. You want the duty cycle to be 1.4/5 times the full range. 70% of 255 is 178.5. Either 178 or 179 should be close enough.
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Thank you for your reply.

I read this article. http://principialabs.com/arduino-pulse-width-modulation/#comment-246 to find out more about PWM

If i did my calculations correctly, shouldn't it be 255(5V) for (90 seconds) and 71.4 (1.4V) for 60 seconds?
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You mean that 1.4/5 isn't 70%? Stupid fingers...
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From what I read in the datasheet, these voltages are for the heater right?  The problem there is that the heater is a 33ohm load.  So at 5V, it needs to draw about 150mA from the Arduino.

So you won't be able to power it directly from the I/O pin.
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It will not need the full amperage, but they say 350mW in the datasheet. I have used some similar sensors, and this is no toy! They will become extremely hot (500 °C)
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