In this post we start exploring the world of Wireless Communication and start with one of the simplest RF modules available for beginners, RF Modules working on 434 Mhz and using Amplitude Shift Keying (ASK) modulation.
In today’s generation, it is often required to switch electrical appliances from a distance without being a direct line of sight between the transmitter and receiver. As you may well know, a RF based wireless remote control system (RF Transmitter & RF Receiver) can be used to control an output load from a remote place.
RF transmitter, as the name suggests, uses radio frequency to send the signals at a particular frequency and a baud rate.
The RF receiver can receive these signals only if it is configured for the pre-defined signal/data pattern.
An ideal solution for this application is provided by compact transmitter and receiver modules, which operate at a frequency of 434 MHz and are available ready-made.
This simple RF transmitter, consisting of a 434 MHz license-exempt Transmitter module and an encoder IC , was designed to remotely switch simple appliances on and off. The RF part consists of a standard 434 MHz transmitter module, which works at a frequency of 433.92 MHz and has a range of about 100 m (10 m- 20 m practically) according to the manufacture. The transmitter module has three pins (Data, Vcc, Gnd) for data and supply.
Note that, for the transmission of a unique signal, an Encoder is crucial. For this, we have used the renowned encoder IC HT12E from Holtek. HT12E is capable of encoding information which consists of N address bits and 12N data bits. Each address/ data input can be set to one of the two logic states. The programmed addresses/data are transmitted together with the header bits via an RF transmission medium upon receipt of a trigger signal. To keep matters simple, we have grounded the address bits in the video/schematic.
Recommended antenna length is 17 cm for 433.92 MHz, and a stiff wire can be used as the antenna.
This circuit complements the RF transmitter built around the small 434 MHz transmitter module. The receiver picks up the transmitted signals using the 434 Mhz receiver module. This integrated RF receiver module has been tuned to a frequency of 433.92 MHz, exactly same as for the RF transmitter.
434MHz receiver module
The receiver module has four pins. Apart from a “ground (GND) ” and a “Vcc” pin, there are two pins for data output.
The “coded” signal transmitted by the transmitter is processed at the receiver side by the decoder IC HT12D from Holtek. HT12D is capable of decoding informations that consist of N bits of address and 12N bits of data. HT12D decoder IC receives serial addresses and data from the HT12D encoder that are transmitted by the RF transmitter module. The “Valid Transmission” (VT) pin also goes high to indicate a valid transmission. A LED can be connected here to visualize a valid RF link.
The RF Receiver circuit can be powered from a standard 5V DC supply. Just as for the RF Transmitter, the aerial (17 cm for 433.92 MHz) has to be mounted as close as possible to the antenna of the 434 MHz RF receiver module.
1) 1 x RF Module Tx + Rx (434 Mhz) (Buy here)
2) 1 x HT 12E (Encoder) + HT 12D (Decoder) + Resistors (1M,50K) (Buy here)
3) 1 x General Purpose PCB (Buy here)
4) 2 x 7805 Based Power Supply Circuit Components (Buy here)
5) 4 x Switches (Buy here) + 5 x 5mm LED (Buy here)
6) Tools (Buy here)
NOTE : Use 2 x 100K resistors in parallel to get 50K value.
Assembled complete kit (Buy here)
Download Schematic from here.
Please follow the video for an easy step by step guide. In case of any questions or queries, feel free to post below.
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