(This circuit first appeared in `The Braille Technical Press`, edited by Robert W. Gunderson, in 1955. Gunderson, W2JIO, designed this `gimmick` to read transmitter meters. It appeared many times since over a 20-year period, included even in commercial aids and appliances for the blind. Bill Gerrey, et al, has never gotten around to generating a p
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rint schematic diagram of the "gimmick" by itself, although it has been part of Smith-Kettlewell adaptive instruments of various sorts over another 30-year span; its circuit appears in those published designs. ) Key components of this VCO are: A hard-to-find NPN germanium transistor (needed for its beta at very low base bias -even though it is non-linear in this service). The transformer is for push-pull output in transistor radios of Yesteryear, but for the time being, many still exist in surplus (even from Radio Shack, 270-1380). The circuit uses a "blocking oscillator", which requires a center-tapped primary winding - specified impedances from 500 to 25, 000 ohms, (center tapped) are appropriate. The transformer secondary winding drives a small speaker; here again, the rated impedance (3. 2 to 16 ohms) is not critical, even though the speaker may be rated at 8 ohms. The center tap of the primary goes to the emitter of a PNP small-signal transistor (type not critical; a 2N2907 was used here). The full primary winding is shunted by 0. 022uF (which increases the loudness). One end of the primary goes through 0. 022uF to the base of the PNP transistor. The other end of the primary winding goes through an SPST on/off switch to the positive of the battery. The collector of the transistor is grounded, as is the negative of the battery. The base of the PNP transistor goes through 22 K ohms to the collector of an NPN germanium...
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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