EE100_Proj1_ReportEE100_PROJ1_PrelabUC Berkeley, EECS Department B. E. BoserEECS 40/42/100 Lab PRJ1: Project 1—Light Gate UID:Light GateIn this project you design, build, and test a “light gate”. A light gate uses a light source directed to a photodetectorto detect interruptions of the light beam. Applications include automatic doors or intrusion alarms.This project includes two main parts:a) Pre-lab: follow the direction given in this document and complete the schematic design of your Light Gatecircuit. Note: You musthave your schematic ready and checked off by a GSI before you start building theactual circuit in the lab (50 % of the grade).b) Lab and Post-lab: Build and test your Light Gate circuit in the lab base on your design. show your workingcircuit to GSI and answer the post-lab questions (50 % of the grade).GuidlinesWe will be using the halogen lamp and solar cell from an earlier lab as the light source and detector and display theoutput on LED (light emitting diode) that turns on (or off) when the light beam is interrupted and off otherwise.You are to design the electronic circuit between the solar cell and the LED.Figure 1 shows a block diagram of the light gate. Since the output of the solar cell is a small current, it needsto be amplified to drive the LED. A Schmitt Trigger is also needed to ensure that the light reliable turns on and offwithout intermediate states that are difficult to interprete. You can tie the LED directly to the output of the SchmittTrigger through a resistor.Suggested planPre-Laba) First we determine how to best use the solar cell as a sensor. We want to maximize the ratio of the output Ss,onwith full light (beam not blocked) at maximum distance to the output Ss,offwith the light blocked at minimumdistance. We use maximum and minimum distance respectively since that’s the most challenging situation ourcircuit has to deal with: if it meets these requirements, it most likely will also work in the other, less demandingsituations.We can either sense the open loop voltage (Vs,on, Vs,off) from the solar cell, or the short circuit current (Is,on,Is,off). Fill in the table below, reusing your measurements from the solar cell lab.Vs,onfor L = 20 cm1 pt.0Vs,offfor L = 10 cm1 pt.1rv= Vs,on/Vs,off1 pt.2Is,onfor L = 20 cm1 pt.3Is,offfor L = 10 cm1 pt.4ri= Is,on/Is,off1 pt.5Which of the two ratios rvand riis larger? Depending on the answer, we are better off treating the solar cell asa voltage or current source and then design our circuit appropriately. Enter your choice in the box below (enterthe textvoltage sourceorcurrent source):HalogenLightSolar Cell AmplifierSchmittTriggerRD=1k:D1Figure 1 Block diagram of the light gate.1 February 23, 2010 PRJ1 v779 http://ucbfeedback.com11 pt.6b) Design the amplifier circuit to gain up this signal to 5 V (Von) for maximum solar cell output. What is the outputvoltage Vofffor Ss,off(S is either V or I, depending on your answer above)? Verify your circuit in the lab.calculated measuredVon1 pt.01 pt.1Voff1 pt.21 pt.3c) Determine thresholds Vth-onand Vth-offfor the Schmitt Trigger to achieve reliable operation for distances be-tween the light and the detector of 10 to 20 cm based on the range of values you determined for Vonand Voff.The output of the Schmitt Trigger should be a reliable indicator of the beam for any distance L between 10 cmand 20 cm.calculated measuredVth-on1 pt.41 pt.5Vth-off1 pt.61 pt.7d) Draw the complete circuit diagram including the amplifier and the Schmitt Trigger. Include all derivations andcalculations of the component values. Attach extra sheet if necessary and draw nicely for full credit.20 pts.8e) Verify your design with SPICE (optional). In practice you would always do this before going to the lab witha circuit of any complexity. Debugging in the lab is much more time consuming than with the simulator andpaper and pencil.2February 23, 2010 PRJ1 v779 http://ucbfeedback.comNote: To simulate the complete circuit, replace the sensor with a piece-wise linear (PWL) current source in SPICEramping the current linearly up and down between zero and an appropriate maximum value. Then perform atransient simulation. Please come to office hours if you have difficulty.f) Ask the GSI to check your schmatic and calculation at the start of the lab session (50 % of the grade).Lab (Experimental Verification)Now you are ready to build and verify the operation of your circuit. It’s a good idea to work in steps. For example,we verify first the light sensor (did that in Lab 1 already) and then the amplifier and the Schmitt Trigger separately.When we have convinced ourselves (using e.g. the DVM) that each part works satisfacorily we connect all partsand verify again.a) Build and test your amplifier circuit in the lab.b) Test Schmitt Trigger circuit in the lab (use the power supply to apply test inputs). Add the LED and verify itsoperation. Use a smaller resistor if it is too dim.c) Once the amplifier circuit and Schmitt Trigger are fully functional, complete the circuit.d) Draw your final complete circuit diagram including all component values (if different from your original de-sign). Draw nicely for full credit. Use extra sheets if needed.1 pt.10e) Show your working circuit to the GSI (for L = 10 cm and L = 20 cm).Post-Laba) Report difficulties you encountered, if any.1 pt.123 February 23, 2010 PRJ1 v779 http://ucbfeedback.comb) Did you make changes to your original design? If so, why?1 pt.13In a product design all involved (marketing, designers, and product, test, and quality control engineers) gettogether at this point to discuss the need for further changes and improvements. Once everyone is happy youwill build a few samples for further testing and show them to potential customers. For these samples you designcustom printed circuit boards (PCBs) and use an attractive package to give the entire system a professional appear-ance. While the salesforce shops the new product around with customers, the product engineers start readyingthe production chain. Often third parties are involved, e.g. to assemble and test the cirucit boards and to fabricatethe case.Password:4 February 23, 2010 PRJ1 v779 http://ucbfeedback.comEE 42/100 Proj1 Light Gate Prelab Summary Name:_____________________________________________________ SID: _______________________________________________________ Answers 0._________________________________________________________
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