This circuit detects motion within approximately 5 inches of a piezo-ceramic element ultrasonic transducer. The detection distance is much smaller than obtainable with other ultrasonic techniques, however, it only requires a single transducer, as opposed to the two-transducer arrangement typically found in other designs. The short-range detection
Click here to download the full size of the above Circuit.
is adequate for many applications, such as proximity-operated commodity dispensers or tamper alarms for merchandise cases. X1 is a directional, piezo-ceramic element, 40kHz ultrasonic transducer driven via R2 by U1, a square-wave astable multivibrator. U1 is tuned to X1`s resonance with RV1. X1 emits ultrasonic energy from its aperture. When X1`s aperture is unobstructed, the AC signal voltage at U2A pin 3 remains constant. Introducing an obstruction near the aperture causes some of the ultrasonic radiation to reflect back into X1`s element, affecting the element`s vibration. This causes a disturbance in the amplitude of the signal voltage, as the reflected energy either cancels or reinforces X1`s emission. U2A is configured as a unity-gain buffer, providing the signal voltage to a half-wave rectifier, CR1, via R3. The anode of CR1 is biased via R4 and R5 so that the lower portion of the signal voltage waveform is clamped. C4 provides a low impedance for the bias. The upper part of the waveform is averaged by R6 and C5. The voltage at the junction of R6 and C5, therefore, is the detected level corresponding to the voltage at X1. U2B, in association with R7, R8, C6 and C7, multiplies the detected level by an AC gain of about 100. The AC-amplified signal appears at U2B`s output, and is further averaged by the long-time constant of R11 and C8. The averaged level is provided to the negative input of op amp U3A. The AC-amplified...
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.....
characters left: