Sensors to Digital I/O or analog?

[Jeep226]

Hello,

I have been working on a project and it requires the use of 3 piezoelectric sensors (listed below). 2 of which are vibration sensors, and the other a force sensor. Nobody in my group are the least bit familiar with electronics or circuits, and the EE majors we talked to talked way over our heads. Anyway they gave us a basic way to set up two of the sensors to the analog inputs, and they said that we can only do two sensors because there aren't enough inputs. For some reason I think it can handle more than just two sensors. I know we are using the analog I/O but is there anyway to use the Digital I/O which have way more ports? We are also using a bread board to connect the sensors. And after the two EE majors left we tried using the force sensor which worked, then we used the vibration sensor with the same set up and it did not work. ANY information would help us! (we were also given a low budget too)

http://www.sparkfun.com/products/9376

http://www.sparkfun.com/products/9196

[lis@jiang]

Hi Jeep226,

Thanks for your question.

Analog signals cannot be read through digital channels, as they are two completely different types of signals.  You can check this document for a brief discussion of the difference.

Which data acquisition card are you using for these sensors?  You can use NI's search to find out how many analog channels you actually have, since it looks like there's some question about that.

Thanks,

Lisa

[Jeep226]

Lisa, 

Thanks for the response. I am also using the MyDAQ. I have seen people on various websites that are able to use numerous sensors, but for some reason the EE majors I talked to said I could only use 2 with the available inputs.

-Jake

[lis@jiang · Accepted solution]

Hi Jake,

If you go to the product page for the myDAQ and click on the Specifications tab, you can see that there are 2 analog input and 2 analog output channels.  Thus you can only use 2 analog sensors with this device.  You can either purchase more myDAQs to increase channel count or switch to another low-cost DAQ card with more AI channels, such as the USB-6008.  Please keep in mind that the myDAQ isn't intended for practical use, only for educational purposes.

Lastly, if you choose to continue using the myDAQ with your piezoelectrics, please also keep in mind that this specific device is supported in the Academic Hardware Products forum.

Thanks,

Lisa

[Jeep226]

thanks you for all your help. Also one last question, if i were to make a simple switch where when pressed two pieces of metal touch to complete the circuit, would that be eligble to go into the digital input of the MyDAQ?

-jake

[lis@jiang]

Good morning Jake,

In order to read an analog signal through a digital channel, you'd have to "digitize" the signal, and that requires an analog to digital converter, which, essentially, is what your myDAQ is doing when you acquire analog data.  A switch would only be able to increase your analog channel count (in this particular case).  If you're okay with not acquiring data simultaneously, you can use your switch to acquire data out of all 3 sensors.

Hope this helps,

Lisa

[Jeep226]

Alright thanks Lisa! 

Also I was doing some testing last night and I was able to hook up 2 sensors in the AI. Which is good, but I did not realize you can't run 2 DAQ assistants at the same time. I was just wondering, am I supposed to only use one DAQ assistant and set up two channels within it? And how would the data output for the DAQ assistant know which AI I want to use?

[lis@jiang]

Hi Jake,

You can collect data out of multiple channels using one DAQ Assistant.  I hope the following screenshot helps!

[Jeep226]

Ok that is great! thanks for all your help!

[victorwilson]

Digital sensors generate what is called a 'Discrete Signal'. This means that there is a range of values that the sensor can output, but the value must increase in steps. There is a known relationship between any value and the values preceding and following it. 'Discrete Signals' typically have a stair step appearance when they are graphed on chart. If you consider a television sets tuner, it allows you to change channels in steps.