Here's a way to get a short range bidirectional RF (Radio Frequency) channel on a microcontroller, using the controller's tristatable I/O pins and on-chip comparator with a few passive components. The range with the firmware and simple I came up with for Atmel AVR controllers allows for low error rate communications over 10 to 15 cm using a 5.5 cm diameter loop antenna on each device. This is the answer to my search for the simplest and lowest cost way to connect instruments on my bench top to my computer and to each other without wires. Its an alternative to short-range infrared; except no need to make sure there is a good optical path between the units.
Click here to download the full size of the above Circuit.
I presently use this system for communications among a wireless alphanumeric 2 line X 16 character LCD (Liquid Crystal Display), a battery operated frequency meter, a four channel 10 bit voltmeter, and a base unit that connects my computer's RS-232 port to the RF channel. These projects are described on other pages on this site. This RF Link also adheres to the "Minimum Mass" product design concept - not using any thing that is not absolutely essential to obtaining the needed function. The Minimum Mass RF Link makes use on a microcontroller's on-chip analog comparator connected to a loop antenna and a pair of bias resistors as a receiver and uses a tristateable output on one of the comparator pins to drive the same loop antenna as a transmitter. I have written code modules for the AT90S2131 and the ATMega 8. The code is fairly small - only 131 bytes for the ATMega8 version, and for hardware resources, it only uses an 8 bit time and the comparator. Though I have only tried this on AVR controllers, I suspect this technique would work well on other controllers, such as the PIC family, equipped with comparitors.
pair of resistors biases the resonant antenna at 1/2 the supply voltage (See Figure 2). This is the sweet spot of the comparator's common mode input range, where the input offset voltage is likely to be minimum, which result in the greatest receiver sensitivity. This is also nice for the transmit mode, when sending...
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: