Using Analog Output to power a sensor

[rhoffman45]

Hello All!

I am currently working on a project involving a MQ-7 Carbon Monoxide Sensor.  This sensor requires a heating cycle consisting of 1.4V for 90 seconds and 5V for 60 seconds.I believe it consumes 350mW during the heating cycle. In the hopes of trying to limit the amout of external hardware I have to use, I was hoping to obtain the 1.4V and 5V  from the output of the myRio Analog channels. However, I have found that although the Analog channel appears to have the correct voltage, it only has 2 mA of current which is insufficient. Does anybody by chance have an idea for how I might increase either the current or the power so that I can successfully power the sensor? Is it even possible to power a device using the analog output channels?

Thank you for your help!

Rachel 

https://www.sparkfun.com/products/9403    

https://www.sparkfun.com/datasheets/Sensors/Biometric/MQ-7.pdf

[NInjaneer_0]

Hello Rachel, 

Is there a particular reason you need to use the AO channels to power your sensor? It looks like the myRIO has a few power output channels that meet your sensors' specifications. See page 23 of the User's Manual. 

http://www.ni.com/pdf/manuals/376047a.pdf

Best,

[rhoffman45]

Hello Cameron! Thank you for your quick response!

The main reason I chose the AO lines to power the sensor was because of the ability to change the output voltage simply by changing the input to the AO VI. I felt that this may be the easiest way to have an alternating voltage output.

As for using the power output channels, these technically do meet the requirements, however I felt it might be easier to have the voltage alternating using software rather than hardware. It's not wise to have two sources of power connected to one terminal of the sensor, so I was attempting to think of a way that I could consolidate the two different voltages into one pin/source.

Do you have any suggestions for how I might use one of the power output pins to generate both +5V and +1.4 Volts in a way that can be alternated in a set pattern?

cheers,

Rachel Hoffman

[NInjaneer_0]

Hi Rachel, 

Thank you for clarifying the issue. Alternating the voltage input for your sensor can be accomplished using the myRIO and a voltage follower circuit. Simply use the myRIO AO as the input to the voltage follower and the +5V power output as the excitation voltage. The AO line will allow you set the output voltage programmatically and the op amp will supply the additional current needed to heat your sensor.