ISLRE-BDGSTKEV2Z

Application Note 1834 Author: Don LaFontaine DAQ on a Stick, Renesas Strain Gauge Introduction Getting Started The “DAQ on a Stick, Renesas Strain Gauge” is one of a series of reference designs highlighting Intersil’s precision products with different microcontrollers. This reference design is a self contained demo showing a complete signal chain solution using Intersil parts and a Renesas microcontroller. The complete reference design is conveniently housed in a USB stick form factor. This compact design draws power through the USB port and uses a Graphical User Interface (GUI) to display the real time voltage readings from a bridge strain gauge or a user supplied sensor. Figure 1 shows the Data Acquisition (DAQ) on a Stick connected to an external foil strain gauge. Installation of the Graphical User Interface (GUI) Software and USB Drivers Figure 2 shows a simplified schematic of the Strain Gauge design. The design uses Intersil’s ISL28134 chopper amplifier, ISL22316 Digitally Controlled Potentiometer (DCP), ISL43741 differential mux, ISL21010 4.096 voltage reference, the ISL26102 24-bit delta sigma converter and Renesas R5F10JBC microcontroller. The GUI Software and USB drivers have to be installed on a PC running Windows NT/2000/XP/Vista/Win7/Win 8 operating system before connecting the ISLRE-BDGSTKEV2Z evaluation board to the USB port. The software and a quick video on the operation of this application demo can be downloaded or viewed from the Intersil website at http://www.intersil.com/en/tools/referencedesigns/Renesas-strain-gauge-reference-design.html. Loading Software Click on the Renesas DAQ on a Stick Software link to load the executable. Follow the on-screen instructions to complete the software installation. The installation program places the user interface software in the C:\Program Files\ IntersilRenesasSGDAQonStick directory. To create a shortcut on your desktop, check the “Create A Desktop Icon” box during the software installation. Launch the application by checking the “Launch Intersil Renesas DAQ on Stick” box, then click the “Finish” button. Video Clip A quick video clip is also provided at the above web link. This video will walk the user through the operation and use of the GUI. Running the Evaluation Software FIGURE 1. DAQ ON A STICK WITH STRAIN GAUGE After software has been installed, plug the ISLRE-BDGSTKEV2Z board into a USB port on the computer and click on the Intersil DAQ shortcut (created in the step above) on the desktop. Figure 3 shows the desk top icon. Ordering Information PART NUMBER DESCRIPTION ISLRE-BDGSTKEV2Z Evaluation Board FOIL STRAIN GAUGE VEE VCC +5V ISL43741 ISL28134 S S ISL26102 10kȍ ISL22316 IN1- 35 0ȍ IN1+ 50ȍ + - 10kȍ DCP TO GUI 24-BIT ADC 50kȍ 0ȍ 35 35 0ȍ ISL21010 VEE VCC Renesas MICROCONTROLLER 50kȍ 50ȍ + 5V VREF R5F10JBC ISL28134 FIGURE 2. SIMPLIFIED STRAIN GAUGE SCHEMATIC May 9, 2013 AN1834.0 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Copyright Intersil Americas LLC 2013. All Rights Reserved Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries. All other trademarks mentioned are the property of their respective owners. Application Note 1834 of 115V/V. Figure 4 shows the external connector inputs, which are used to connect the sensor to the circuit shown in Figure 2. FOIL STRAIN GAUGE 1. To connect the foil gauge supplied with the evaluation board, plug the wires into the “S” ports (either top row or the bottom row, the columns are connected) on the DAQ Stick. FIGURE 3. DESKTOP ICON The green LED on the DAQ on a Stick board should be on at this time. When the software starts, the DAQ Startup screen shown in Figure 5 will appear. With the DAQ on a Stick connected, the USB Status indicator will display “Connected 0x2032”. The assigned HID code for this application is 0x2032. This is verification the software is communicating with the board. If the DAQ on a Stick is not connected, or a problem exists with the demo, the message will read “HID Device Not Found”. If this occurs, click on the “Test USB Connection” button to see if this enables the connection. If not, try disconnecting and re-connecting the device or restarting the software. From the DAQ Start-up Screen (Figure 5), the user can click on the Instantaneous Voltage button to get a single voltage reading, select the sensor input they want to measure and adjust the gain of the amplifier, or click the Start button to go to the Measurement Display screen, as shown in Figure 6. At this point the green LED on the board will go off. 2. Connect the opposite end of the wires to the far edges of the foil gauge board. Reference Figure 5. USER SUPPLIED SENSOR 1. To connect a user supplied sensor, plug the wires into the IN+ and IN- ports shown in Figure 4, then select the “Customer Supplied” option, as shown in Figure 5. This will cause the ISL43741 differential mux to switch the inputs. Once the customer supplied option is selected, the user will have the option of changing the amplifiers’ gain for the best measurement. 2. The DAQ on a Stick also provides a 5V supply and Ground connection for possible use by the customer’s sensor network. Connecting the Sensor The ISLRE-BDGSTKEV2Z reference design gives the user the option to measure the strain on a foil gauge (supplied with the evaluation board) or connect their own sensor and monitor the voltage reading on the GUI screen. The user will select the “Sensor Supplied with the Demo” or “Customer Supplied” sensor by clicking the appropriate radial button at the bottom of Figure 5. The foil gauge is the default value in the GUI with a gain FIGURE 4. SENSOR CONNECTOR 32 FIGURE 5. GUI START-UP SCREEN 2 AN1834.0 May 9, 2013 Application Note 1834 FIGURE 6. GUI MEASUREMENT SCREEN Figure 6 shows the Measurement Display screen. From this screen, the user can stop and start data collection, adjust the minimum and maximum X & Y axis and go back to the set-up screen by clicking on the Show Main button. A calibrate button is provided to zero out the voltage reading when the board is not under strain. This helps to give an accurate reading from time zero, and is required because the board does not always return to the same deflection point after a strain is applied to the board. Design Considerations ISL28134 The ISL28134 is an ideal choice for the input amplifier for a strain gauge design. The ISL28134 uses auto-correction circuitry to provide ultra low offset voltage (2.5ƫV), and low offset temperature drift (15nV/°C). The very low 1/f noise corner