Circ Close
there is one circuit in the link provided…(urgent)?
http://www.sentex.ca/~mec1995/circ/sensor2.htm
please tell me the voltage value that should came to the base of the transistor if the value is close to 6 volt..then what is the issue with circuit..
lm324 opamp is used!!
what happens to the voltage level across LDR..when light falls over it.
reasons!!
thanks in advance!
The opamp is being used as a simple comparator. Substituting one section of an LM324 for the 741 is OK. You are comparing the voltages of the taps of 2 voltage dividers. The resistance of the Light Dependent Resistor drops when light falls upon it which means that the voltage at the junction of LDR1 and R1 will rise.
If the voltage at the (+) input of the opamp is higher than the voltage at the (-) input, the output of the opamp will be close to the positive supply voltage, or almost 12 volts.
If the voltage at the (+) input of the opamp is lower than the voltage at the (-) input, the output of the opamp will be close to the negative supply voltage, or in this case, close to zero volts.
Resistors 4 and 5 limit the output voltage to about 1 volt when the output of the opamp is high which is more than the transistor needs to be turned on. If the transistor is good and connected correctly, you should only see the voltage drop across the base – emitter junction ~ 0.6 volts.
If the output of the opamp is low, you should see close to zero volts at the base of the transistor.
Don
Circ – Close Your Eyes