The LED is wired in series with a 330Ω resistor. Assuming the LED has negligible resistance, the total resistance of the circuit is 330Ω. According to Ohm’s Law, the current drive with a 5VDC power supply from the digital line would result in 5V÷330Ω= 15.15mA. As stated in the specification sheet for the LED that is referenced at the bottom of the document, the Led can handle a current up to 20mA, and is recommended to be used with 16 to 18mA; so at 15.15mA we will be safe. The LED requires a positive input on the longer lead side and a negative input on the shorter side, as seen in Figure 1 above. We will supply power to this circuit using Digital Line 0 of the myDAQ, and ground the circuit to Digital Ground of the myDAQ.
Figure 2: Wiring Diagram
The user interface we created has a Boolean push button switch to control the SSR to be open or closed, which will then turn the fan on or off.
Figure 3: LabVIEW Front Panel
In LabVIEW we need to create a front panel Boolean array control to output a 5V digital signal on Line0 to our Solid-State Relay. This Boolean value is input into our DAQ Assistant which will output the corresponding value to the NI myDAQ digital line. In digital Boolean logic, a Truecorresponds to a 5V signal, and a False corresponds to a 0V signal. Therefore, a True will close the SSR, and complete the fan and power supply circuit, allowing power to flow to the fan.
Figure 4: Coding Block Diagram
The LabVIEW diagram looks very similar to the coding block diagram, except the SSR is not included.
Figure 5: LabVIEW 2009 Block Diagram
(The attached LabVIEW code snippet can be dragged-and-dropped to a LabVIEW block diagram, use attached PNG file. After locating the PNG file, just drag the file icon onto a blank block diagram, as if you were dragging the file onto your desktop.)
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