This project uses a magnetic reed switch, a NerdKit, and set of computer speakers to frighten unsuspecting visitors at the door. In covering constructing this project, we get a chance to go over some pretty neat engineering concepts: digital audio, data compression using Huffman codes, and outputing audio via PWM with analog filtering. To detect whether the door was opened or closed,
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we used a magnetic reed switch, like the kind used in wired alarm systems. This one from Amazon illustrates the basic concept. One part has a magnet, and would be mounted on the moving door or window. The other part has a magnetic-field-sensitive switch, and this one has three screw terminals for the switch contacts. For the switch we purchased, we wired the "COM" common terminal to ground on our breadboard, and connected the "NC" normally closed terminal to our microcontroller pin PC5 (ATmega328P pin #28). For our part, this meant that the switch was closed (connected) when the magnet was nearby. As we discussed in our Digital Calipers DRO video, we can use the microcontroller`s built-in pull-up resistors to easily read from a switch or button with no extra components. As explained in the video, for variable-length codes, we generate a tree of binary ones and zeros corresponding to a sequence of bits, and each "leaf" of the tree corresponds to a symbol being output from the decoder. By visualizing this as a tree, we automatically enforce the constraint that no complete code for a symbol is the contained within the beginning of the code for a different symbol. Huffman coding is the specific way to generate this tree in an optimal way. By optimal, we mean that if we know ahead of time the probability distribution of all of the different symbols occuring in our information stream (and assume them to be independent), we...
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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