Finally I have found a use for a bunch of DIP-style RF relays I acquired in a grab-bag from a discount electronics shop some time ago. These babies are sealed totally, and rf shielded with low contact capacitance. Perfect for VHF frequencies. They are 12 volt and have a fairly decent coil resistance, although I wish they were latching style. I hav
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e several purchased antenna switches but they are all the same. Every few months they need to be pulled apart and cleaned as the contacts oxidize quickly. Perhaps there are better ones out there but frankly I`m sick and tired of looking by "buying and trying. " The solution of using relays isn`t without it`s draw backs, i. e. power consumption, but it`s minimal and can be turned into low draw mode by selecting no relay. As can be seen on the right side of the schematic, the 4 outputs are all VHF related. As the antenna will be 1/4 wave, SWR won`t be a problem and the EXT can be used for TV signals. This switch doesn`t just select single outputs but counts binarily through them all so 2 or more can be connected at the same time. Caution must be used when using the VHF (2 meter) transmitter so one of the buttons has been designated as an "instant set" to that output only. ( D3 held high ) The LEDs being switched on with the realys show the status. Red alone must be on for transmitting. The 7414 gates are Schmidt triggers, famous for their ability to debounce switches. Once the zero crossing has occurred as button is pressed, it must be a certain voltage above that to flip...
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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