The LDR specifications mainly include maximum power dissipation, maximum operating voltage, peak wavelength, dark resistance, etc. The values of these specifications mentioned below. The light-dependent resistor is very responsive to light.
When the light is stronger, then the resistance is lower which means, when the light intensity increases then the value of resistance for the LDR will be decreased drastically to below 1K. When the light drops on LDR, the resistance will be decreased and when the resistor is placed in the dark then the resistance will be increased which is called dark resistance.
If any device absorbs light then its resistance will be reduced radically. Some kinds of photocells are not at all sensitive to a specific range of wavelengths because it depends on the used material. Once light rays fall on a photocell, the resistance will be changed in 8 ms to 12, while it uses few more seconds to rise the resistance back again to its early value once the light is removed.
So this is known as a recovery rate of resistance. In audio compressors, this property is applicable. The classification of LDR can be done based on linearity or photosensitive materials. Light-dependent resistors are simple and low-cost devices.
These devices are used where there is a need to sense the presence and absence of light is necessary. These resistors are used as light sensors and the applications of LDR mainly include alarm clocks, street lights, light intensity meters, burglar alarm circuits. For a better understanding of this concept, here we have explained one project namely; power conserving of intensity controlled street lights using LDR.
To overcome this problem, here is an alternative method using LEDs i. The proposed system is built to overcome the drawback of the present-day HID lamps. The proposed system determines the usage of light-emitting diodes as a light source and its adjustable intensity control according to the requirement.
These lights consume less power, as well as the life span of these lights, which is more compared to conventional HID lamps. The most important feature of this project is, the light intensity can be controlled according to necessity during nighttime, which is not possible in HID lamps.
LDRs light-dependent resistors are used to detect light levels, eg in automatic security lights. Their resistance decreases as the light intensity increases. In the dark and at low light levels, the resistance of an LDR is high, and little current can flow through it. When they are used in the form of photoresistors, then these materials act as resistive elements only where there is absence of PN junctions. This results in the device to become entirely passive in nature. Intrinsic Photoresistor: The photoconductive material which is used by a specific photoresistor type enables the charge carriers to get excited and jump to the conduction bands from their initial valence bonds respectively.
Extrinsic Photoresistor: The photoconductive material which is used by a specific photoresistor type enables the charge carriers to get excited and jump to the conduction bands from their initial valence bonds or impurity respectively. This process requires non-ionized impurity dopants which are also shallow and requires this to take place when light is present.
The design of the photocells or extrinsic photoresistors is done specifically considering the long wavelength radiations such as the infra-red radiations in most of the cases.
But the designing also considers the fact that any type of thermal generation needs to be avoided since they are required to operate at temperatures which are very relatively low. The number of natural methods which are commonly observed for the manufacturing of the photoresistors or the light dependent resistors is very few in number. A resistive material sensitive to light is employed by the light dependent resistors for constant exposure to light.
As discussed above, there is a specific section which is processed by the light sensitive resistive material which is required to be in contact with both or one of the ends of the terminals. A semiconductor layer which is active in nature is used in a general structure of a photoresistor or a light dependent resistor and an insulating substrate is further used for depositing the semiconductor layer.
In order to provide the semiconductor layer with the conductivity of the required level, the former is doped lightly. Thereafter, terminals are connected appropriately across the two ends. The contact area of the resistive material is minimized to ensure that when the device is exposed to the light, it undergoes a change in its resistance efficiently.
In order to achieve this state, it is ensured that surrounding area of the contacts is doped heavily which results in the reduction of the resistance in the given area. The shape of the surrounding area of the contact is designed to be mostly in the interdigital pattern or the zig zag form. This enables the maximization of the exposed area along with the reduction in the levels of the spurious resistance which in turn results in the enhancement of the gain by contracting the distance between the two contacts of the photoresistors and making it small.
There is also a possibility of the usage of the semiconductor material such as polycrystalline semiconductor depositing it on a substrate. One of the substrates which can be used for this is ceramic. This enables the light dependent resistor to be of low cost. The most attractive point of the light dependent resistor or a photoresistor is that it is of low cost and thus is widely used in a variety of electronic circuit designs. Although the photoresistor lacks various features which are found in a phototransistor and a photodiode, it is still an ideal choice for a variety of applications.
Thus, LDR has been continuously used for a long period of time in a range of applications such as photographic light meters, burglar and smoke detectors, in street lamps to control the lighting, flame detectors, and card readers. The factor which determines the photoresistor properties is the material type which is used and thus the properties can vary accordingly. Some of the materials used by the photoresistors possess constants of very long time.
Thus, it is quintessential that the photoresistor type si selected carefully for specific applications or circuits. Light dependent resistor or LDR is one of the very useful sensing devices which can be implemented in many different ways for processing light intensity.
The device is cheaper compared to other light sensors, yet it is able to provide the required services with utmost efficiency. The above discussed LDR circuits are just a few examples which explains the basic mode of using an LDR in practical circuits. The discussed data can be studied and customized in several ways for many interesting applications.
Have questions? Feel free to express through the comment box. If you have any circuit related query, you may interact through comments, I'll be most happy to help! Your email:. Hi Swagatam, I am trying to design a circuit that will trigger a CK alarm chip.
I want the circuit to trigger based on light. Say the alarm module is placed in a drawer and when someone opens the drawer, the alarm sounds. I am using 3v battery supply. This works good. I have tried several power on delays with mixed success. I have tried your delay on timer using transistors, resistors and capacitor. I have tried delay timer. They all work, but I still get the hum from the CK which gets louder just before the chip fully triggers.
Hi Norman, did you confirm the leakage by measuring it with a multi-meter? High Swagatam, I found a circuit on the internet that uses a timer as follows: Pin 1 is grounded.
Pin 4 and Pin 8 are 5v. Pin 2 and Pin 6 are shorted together. It works great. I breadboarded it with a uF electrolytic capacitor which give me a delay of about 17 seconds. I would like a little longer delay, but the largest SMD capacitor I have is a tantalum capacitor of uF. Is there a way to increase the delay, say to 25 seconds using this circuit with my capacitor limitations. Hi Swagatam, The latest power on delay is not causing any hum on the CK The takes up a little more room on the PCB but for this type circuit, it seems to be a superior design.
The timing and sound are very clear. My second post describes the design I am using. I may try to fit to caps in parallel to increase the delay time. However when working with infrared, care must be taken to avoid heat build-up caused but he elating effect of the radiation. One important aspect associated with photoresistors or light dependent resistors is that of the latency, or the time taken for the electronic component to respond to any changes.
This aspect can be particularly important for a circuit design. However when the light changes take place over a period of time they are more than adequate. The rate at which the resistance changes is called the resistance recovery rate. It is for this reason that one of the specifications normally quoted in the electronic component datasheets for photo-resistors is the dark resistance after a given time, typically in seconds.
Often two values are quoted, one for one second and another for five seconds. These given an indication of the latency of the resistor. Photoresistors are found in many different applications and can be seen in many different electronic circuit designs. They have a very simple structure and they are low cost and rugged devices. They are widely used in many different items of electronic equipment and circuit designs including photographic light meters, fire or smoke alarms as well as burglar alarms, and they also find uses as lighting controls for street lamps.
Extrinsic photoresistors are provide sensitivity for longer wavelengths and as a result they are popular in various electronic circuit designs as info-red photodetectors. Photoresistors can also be used to detect nuclear radiation. LDRs are very useful electronic components that can be used for a variety of light sensing applications and their associated electronic circuit designs. As the LDR resistance varies over such a wide range, they are particularly useful, and there are many LDR circuit designs available beyond any shown here.
In order to utilise these electronic components, it is necessary to know something of how an LDR works, which has been explained above. Typical leaded light dependent resistor What is light dependent resistor, LDR or photoresistor A photoresistor or light dependent resistor is an electronic component that is sensitive to light. The basic format for a photoresistor is that shown below: Photoresistor structure The active semiconductor region is normally deposited onto a semi-insulating substrate and the active region is normally lightly doped.
Photoresistor structure showing interdigital pattern to maximise exposed area. Types of photoresistor Light dependent resistors, LDRs or photoresistors fall into one of two types or categories: Intrinsic photoresistors: Intrinsic photoresistors use un-doped semiconductor materials including silicon or germanium. Photons fall on the LDR excite electrons moving them from the valence band to the conduction band. As a result, these electrons are free to conduct electricity.
The more light that falls on the device, the more electrons are liberated and the greater the level of conductivity, and this results in a lower level of resistance.
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