In this project we will make the one to many communication using RF . Main features of this project is advantages of RF . We are using RF which will keep your conversation and data secure from others. In this sytem we will make master slave system . In which master can send data and voice message to any slave . he has the full control on the system. In this project we are taking the example of office system. In this project officer can select the user with keyboard and can talk to any one by selecting from keyboard.
In this project we will learn about how to use RF for communication purpose. RF need not to introduce. Everybody although he/she may be from any field know about RF. RF as we know a reliable, low cost, flexible, large bandwidth communication medium. IN one to many communication we will control many speakers from our system and can send data on any particular speaker.
In this project we can control any electrical appliances like speakers through DTMF dialing circuit for remote purpose . When we want to control any electrical appliances through DTMF dialing circuit. Now again we press the switch on/off code to on/off any electrical appliances. With the help of this code unit is on and base unit give a acknowledge pulse for on and off separately.
DTMF Encoder Circuit:- in this circuit we will use IC91214 for no of devices. We will add keyboard with this IC. Ethis IC have option to generate 16 different pulses with different frequencies. These dual tone multi frequencies can be decoded at receiver side with IC8870 . these IC are esily available in market. We will use LASER for data transmission.
- 1. DTMF DECODER
In dtmf decoder circuit we use ic 8870 ic. IC 8870 is a dtmf decoder ic. IC 8870 converts the dual tones to corresponding binary outputs.
DTMF SIGNALLING. Ac register signaling is used in dtmf telephones, here tones rather than make/break pulse are used fro dialing, each dialed digit is uniquely represented by a pair of sine waves tones. These tones ( one from low group for row and another from high group fro column) are sent to the exchange when a digit is dialed by pushing the key, these tone lies within the speech band of 300 to 3400 hz, and are chosen so as to minimize the possibility of any valid frequency pair existing in normal speech simultaneously. Actually, this minimisator is made possible by forming pairs with one tone from the higher group and the other from the lower of frequencies. A valid dtmf signal is the sum of two tones, one from a lower group ( 697-940 Hz) and the other from a a higher group ( 1209-1663 Hz). Each group contains four individual tones. This scheme allows 10 unique combinations. Ten of these code represent digits 1 through 9 and 0. . tones in DTMF dialing are so chose that none of the tones is harmonic of are other tone. Therefore is no change of distortion caused by harmonics. Each tone is sent as along as the key remains pressed. The dtmf signal contains only one component from each of the high and low group. This significaly simplifies decoding because the composite dtmf signal may be separated with band pass filters into single frequency components, each of which may be handled individually.
First ic of this section is ic 74154. IC 74154 is bcd to decimal decoder. 74154 is active low ic. Pin no 20,21,22,23 is connected to dtmf decoder ic.
Pin no 18 and 19 of this ic is connected to the collector of one npn transistor Base of the npn transistor is connected to the pin no 15 of the ic 8870. When dtmf decoder decode the signal at that time pin no 15 is on for a time and acknowledge the signal. This signal is fed to the base of NPN transistor through 1 kohm resistor. When this signal is coming then 74154 is on and gives a output.
Then output of 74154 is active low. We will use IC 74ls 74 or transistors to invert the active low output. After that we will use flip flop & SCRs or relays to control & to give 220v Ac to devices for switching purposes.