A Light Dependent Resistor (aka LDR, photoconductor, photoresistor, or photocell) is a component used commonly in electronics which has a resistance which decreases as the intensity of the light hitting its surface increases and visa versa. A typical light dependent resistor is pictured above together with (on the right hand side) its circuit diag
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ram symbol. The vast majority of LDRs are made from cadmium-sulphide (CdS), and they are very cheap, but also not very accurate. They are very good for detecting changes in light levels and determining if it is `dark` or `light`, but without individual calibration they not suitable for accurately measuring light levels. Pictured below is a typical light dependent resistor. It has two wire leads which terminate in the face of the light detector - the two metal dots you see are the ends of those electrodes. The main body of the light detector component is made of ceramic - an excellent insulator. On the face of the ceramic a thin strip of cadmium sulphide is coated in a zig-zag pattern (to maximise the length of the strip while keeping the component small) which is connected at each end to an electrode. The front face is then coated in clear plastic, epoxy, glass, or similar. Cadmium-sulphide is a high resistance semiconductor, and is chosen for light detectors as it gives the same spectral response as the human eye - i. e. it `sees`/responds to the same range of wavelengths of light that we can see. Specifically, cadmium-sulphide is a photoconductive material. That means that photons of light hitting it with sufficient energy will release electrons from their atomic bonds. When a negatively charged electron is freed by a photon of light, it leaves behind a positively charged `hole`. When a voltage is applied across the two...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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