9electronicscale-atmel

9electronicscale-atmel - Electronic Scale Laboratory ES-1...

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Electronic Scale Laboratory ES-1 © San José State University Department of Mechanical and Aerospace Engineering rev 2.1 20OCT2007 The Electronic Scale Learning Objectives By the end of this laboratory experiment, the experimenter should be able to: Explain what an operational amplifier is and how it can be used in amplifying signal sources Configure, build, and test several common amplifier types. Explain what a Wheatstone bridge is and how it is used in measurement systems Interface an analog signal source to an A/D converter on a microcontroller and write a program to determine its voltage Build a digital electronic scale using strain gages, an amplifier, an A/D converter, and a microcontroller Components Qty. Item 1 Atmel ATmega 128 microcontroller with STK500 and STK501 interface boards, and serial cable 1 Solderless breadboard 1 LF353 dual operational amplifier 1 INA126 instrumentation amplifier 1 Cantilever beam assembly with strain-gauges mounted on the top and bottom surfaces near the base 1 ea. 1 k resistor, 4.7 k resistor 2 ea. 10 k Ω resistors, 200 k resistors 1 ea. 1 k Ω trim pot, 100 k Ω trim pot 1 ea. 0.1 μ F capacitor, 10 μ F capacitor Introduction The Devices Figure 1 shows two common packages for operational amplifiers. The single package on the left contains one operational amplifier. The LF741 was one of the earliest IC op-amps and is still widely used. There are many, many varieties of op-amps available today (see http://focus.ti.com/lit/an/slod006b/slod006b.pdf for example). In this lab we will be dealing with op-amps designed for small signal amplification. There are also power op-amps that are designed to source or sink relatively large currents at relatively high voltages. Small-signal single op-amp IC’s are usually pin-compatible with the ‘741, but one should always check the data sheets to be sure. One of the op-amps we will use in this lab experiment is the LF353. It contains two independent op-amps as shown. Some op-amps come in quad-packages that contain 4 independent op-amps. Op-amps are active devices, which means they must be powered in order to function. The typical configuration will use symmetrical positive and negative supply voltages (V S ) in the
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Electronic Scale Laboratory ES-2 © San José State University Department of Mechanical and Aerospace Engineering rev 2.1 20OCT2007 range between ± 5 V and ± 15 V. There are some op-amps that are designed to work with single-sided supplies, i.e., where –V S is ground, and +V S is +5 V to +15 V. 7 1 2 3 4 5 6 8 - + 7 1 2 3 4 5 6 8 ‘741 type, single LF353, dual Balance Balance - input + input - V S + V S Output N. C. Output A Output B - V S + V S - input A + input A + input B - input B A B - - + + Figure 1 Examples of single and dual op-amp IC packages. We will use the LF353 dual op-amp in this experiment. Procedure
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This note was uploaded on 09/08/2010 for the course ME 106 at San Jose State.

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9electronicscale-atmel - Electronic Scale Laboratory ES-1...

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