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PHOTOCELL_BRIDGE

2016-05-17 00:19  
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PHOTOCELL_BRIDGE
PHOTOCELL_BRIDGE
Radio Shack 276-116 cadmium sulfide photocell is connected in Wheatstone bridge circuit. When bridge is bal-anced, RS741C opamp connected to opposite comers of bridge receives no voltage and meter reads zero. Light on photocell unbalances bridge and gives meter deflection. Can be used as high-sensitivity light meter. Adjust R3 until meter reads zero with photocell covered while R5 is at maximum resistance,adjust R5 until needle moves away from zero,rezero with R3,and repeat procedure until meter can no longerbe brought to zero,Sensitivityis now maximum,and uncovered photocell Will detectfiame from candle at 20 feet.-F.M.Mims,''Integrated Circuit Projects,vol 4,''Radio Shack,Fort Worth,TX,1977,2nd Ed.,p 29-35.