To develop sensor-based test and measurement systems, students need a sensor prototype design platform with excellent compatibility and open and unlimited sensor extendibility. With extensive curriculum design, electronic design contests, and extracurricular test and measurement sensor applications, systems should be efficient and help students save time.
The NI myDAQ sensor prototype board (mySensor), which meets all aforementioned requirements, is an NI miniSystem designed specifically for NI myDAQ. It is based on NI virtual instrument technology and supports SPICE circuit simulation technology based on a sensor prototype test and measurement circuit.
NI myDAQ Sensor Prototype Board Design
mySensor follows a generic sensor-based test and measurement application workflow, as shown in Figure 1.
Most electrical sensor output signals are weak when measuring a physical signal (sound, light, magnetic field, or temperature) and need to be amplified, filtered, and shaped through signal conditioning modules. After the modules condition the signal to an optimal range suitable for data acquisition device input channels, NI myDAQ acquires it, and LabVIEW reads and processes it.
Because NI myDAQ is meant to be used outside of the lab as well, the mySensor board dimensions cannot be too large. The maximum printed circuit board (PCB) dimension is 5,950 mm x 3,075 mm. During the mySensor design process, we optimized each sensor and conditioning module for reuse. Each independent module is 1,425 mm x 1,025 mm. Modules are extended and replaced in an interleaved manner.
Because the mySensor includes conditioning modules that need power, it also incorporates a +15 V/-15 V power supply converted from a USB +5 V to DC-DC, which is easily powered by USB.
The mySensor Schematic Diagram and PCB Design
We used the seamless integration of Multisim 11.0 and Ultiboard 11.0 to complete the entire mySensor process, from schematic diagram to PCB. The mySensor schematic diagram design process using Multisim 11.0 is divided into seven steps, as shown in Figure 3, and the mySensor PCB design process in Ultiboard 11.0 is divided into seven steps, as shown in Figure 4.
Figure 5 shows the differential amplifier module schematic diagram in Multisim, combined with a function generator and 2-channel oscilloscope. With the Multisim interactive simulation feature, we run the circuit simulation and adjust the gain potentiometer slider at the same time. We interactively observe the output signal, distortion, and circuit amplification factor. In addition, we can load the Potter tester to test amplifier module amplitude-frequency characteristics. Using NI ELVISmx simulated and real data, we can compare the two to improve circuit design and achieve the best parameters.
As shown in Figure 6, we designed the mySensor PCB layout using Ultiboard. First, we determined proper board dimensions. Board module layout should make sensor connection convenient. We put six independent foldable modules on the right side for easy extension, the NI myDAQ connector on the left, and the USB power supply interface at the top. Using the Ultiboard 3D scene function, we can see the mySensor represented with mounted components, as shown in Figure 7.
After Multisim schematic design and Ultiboard PCB design, we can deliver the generated Gerber to the PCB manufacturer to complete the design phase.
The mySensor Experiments
All the mySensor sensor test and measurement applications can use the NI ELVISmx soft front panel instruments, including DMM (digital multimeter); Scope (oscilloscope); FGEN (function generator); Bode (Potter instrument); DSA (dynamic signal analyzer); ARB (arbitrary waveform generator); DigIn (digital input); and DigOut (digital output), shown in Figure 8.
In addition to NI ELVISmx soft front panel instruments, we can also use LabVIEW to program them and perform specialized testing procedures for each sensor, as shown in Figure 9.
Minimizing Risk and Maximizing Results
After three days of design, seven days of manufacturing, and assembling and debugging, the mySensor test data is consistent with expected design requirements. We determined that using an NI schematic diagram and PCB design solution reduces developmental risks.
Using NI myDAQ and LabVIEW, we quickly prototyped the mySensor test and measurement system based on NI myDAQ, and therefore greatly enhanced the sensor test and measurement prototyping solution for college and education.
East China Jiaotong University