Lesson 7 Light-Dependent Resistors

Chapter Lesson 7 Light-Dependent Resistors

Electronic Circuits for the Evil Genius Second Edition 64 Lessons with Projects
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Electronic Circuits for the Evil Genius Second Edition 64 Lessons with Projects

  • 4.Use the 100-kilo-ohm potentiometer. Record your results.a.Measure the resistance between the two outer legs A and B. ______ b.Adjust the knob and check the resistance between A and B again. ______ c.Adjust the knob about halfway. Measure the resistance between the left and middle legs—A and C. ______ d. Turn the knob a bit and check again. Note any change. ______ Explain what is happening, relating that to thecarbon ring shown in Figure L6-3.__________________________________________________________________________5.Make sure that you have the battery hookedup properly through the power diode as notedon the schematic.6.As you turn the shaft of the potentiometer, theLED should brighten and dim. Explain whatis happening.__________________________________________________________________________7.Why is there a 470-ohm fixed resistor in thiscircuit?_____________________________Breadboarding the CircuitNote the similarities of the schematic shown inFigure L6-7 and the picture of the circuit displayedin Figure L6-8. Lesson 7Light-Dependent ResistorsAnother variable resistor is the light-dependentresistor (LDR). The LDR changes its ability toconduct electrons with the change of light. It iscommonly used to turn equipment on automaticallyas night falls. Some cars use it as the input to theswitch that turns on headlights as conditionschange, even as they drive through a tunnel. Thesymbol for the LDR is shown here in Figure L7-1.There is no room to place a value on mostLDRs. They are ordered and supplied in specificvalues. An easy way to measure the maximumresistance is to measure it in darkness.Lesson 7 ■Light-Dependent Resistors 21Figure L6-7Figure L6-8