![]() Chip select pin CS is connected to ground to make chip always enable.Interrupt output pin INTR from ADC is connected to external interrupt 1 pin INT1.Control pins RD and WR of ADC are connected with port P3 pins P3.7 and P3.6 respectively.Digital outputs DB0 – DB7 are connected to port P1 of AT89C52 microcontroller.The voltage across biasing resistance is given as analog input to ADC0801 LDR is connected between Vcc supply and ground through a 10K resistor that gives it bias. ![]() Software program and logic explanation are given afterward. So ready to build the project? Here is the circuit diagram followed by description and operation. if LDR resistance varies from 1 K to 25 K (in full light to darkness) select R as 10 K. Just measure the value of LDR resistance in darkness and full light and select the value of R as the mid value of this range. Also, the value of fixed resistance R should be chosen after calculations such that as the LDR resistance varies from darkness to full light the voltage V should change from 0 to 5 V. In this project, LDR is used with pull down resistance configuration. So we cannot use this second configuration because we want an increase in voltage with the increase in light intensity. So in this connection as LDR resistance increases- means light decreases, the voltage increases, and vice versa. In figure (b) the voltage equation changes to So as LDR resistance decreases – means light increases, the voltage increases, and vice versa 1: Circuit Diagram of LDR based Voltage Divider Networks used as Light SensorsĪs shown in figure (a) the voltage at the junction of LDR and R (fix value resistance) V is If it is connected in the pull down configuration the voltage increases as light intensity increases and if it is connected in the pull up configuration the reverse will happen. Let us discuss this in somewhat more detail manner.Īs shown in the figure to vary the voltage as per the change in light intensity and the resistance of LDR, the LDR can be connected with fixed value biasing resistance in pull up configuration or pull down configuration. The change in analog voltage is converted into digital equivalent using ADC and this digital value is read by microcontroller. LDR has to be given biasing voltage along with pull up or pull down resistance so that change in resistance is converted into change in voltage. However, microcontroller cannot detect the change in resistance directly. It also indicates how much light inside room like “full light”, “good light”, dim light” etc. It uses microcontroller AT89C52 and LCD to display light intensity. With a minor change in the circuit, it can be used to measure outdoor light intensity also. In the given project, LDR is used to measure light intensity inside the room. So the change is the resistance of LDR can be a measurement of the amount of falling light. Thus as light intensity increases, the conductivity increases (resistance decreases) and vice versa. ![]() The kinetic energy of photons is given to electrons – that makes more number of free electrons – that leads to increase in conductivity of the device. As more light falls on it, more number of photon strikes. It’s made up of such material whose conductivity varies as per light falls on it. It works on the principle of photoconductivity. We all know that LDR (light dependent resistor) can be used as one of the most suitable light intensity detector because of its working principle. Light intensity meter using AT89C52 microcontroller
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