Operated either by AC or DC, this Radio frequency based remote controller usually controls the load, may be two or more, situated at certain distance from controller. this systems is based on functioning of two major parts viz. i) The transmitter ii) The receiver. The basic operation that controls this system are modulation and demodulation. Modulation is the basic part of transmitter whereas the demodulation is placed in the receiving part of the system. The objective of the system is controlling the load that are in the receiving part by triggering it by sending RF through transmitter. As the result, the system will be acting as a remote controlled device. the system is to be established with the help of communication link i.e. radio frequency. the required is set up by considering the type of load and the distance of the receiving unit. Initially the circuit is designed for two loads. however the number is load can be incremented as desired.
the transmission section deals with sending the signal for controlling load.. The transmitter usually comprises of
i) Oscillators,
ii) Modulator
iii) Filter
The loads are fixed with their desired modulating frequency. The desired carrier frequency is set up for signal transmission.
The receiving section comprises of units for amplifying, demodulating and filtering. Which sends required signal to respective loads for carrying operation after verifying it. It also comprises of logical circuit for controlling the loads. The demodulation operation is carried by the FM receiver and the logic circuit controls the desired sequential operation for loads.
The transmitter Section
i. Oscillator
The two oscillator generates the modulatied frequency of 1.2 KHz and 10 KHz for the two load control. The oscillators used here are Wein Bridge Oscillator.
ii. Filter
The two ferquency are filtered using a filter to minimise the noise and tranmission of effective signal. The two filters used are the second order Sallen Key filters, one is 1.2 KHz low pass and the latter is 10 KHz high pass.
iii. Modulator/ Oscillator
This acts as a radio frequency generator for the transmission. The 102 MHz oscillator using the tank circuit generates the carrier frequency ready for the tranmission from the transmitter.
1.2.2.2 The Receiver Section
i. RF Amplifier
It amplifies the signal received from the transmitter. The output of the transmitter is about 15-20mV in amplitude. This amplitude is amplified, in order for the signal to control the loads in the receiver section.
ii. FM Demodulator
It demodulates the transmitted signal. The modulated signal of the 1.2 KHz and 10 KHz is demodulated here to receive the transmitted frequency for the load control. The FM receiver here is the FM demodulator.
iii. Filter
The Filter in the receiver part is same as in the transmitter part. The Filter is used in order to differentiate the two frequencies. The receiver then identifies which signal had been transmitted(1.2 KHz and 10 KHz).
iv. Logic
This part consists of logic for controlling the load. The turning on and off of the load is done with the same trigger. This is made possible using the logic circuit which consists of the Schmitt trigger along with the timer circuit. Thus formed output will be used in sequential circuit for the load control.
Methodology
The radio frequency remote controller system will operate at the carrier frequency of 102 MHz. The methodology can be summrized in the following ways:
The Transmitter Section
§The radio frequency of 102 MHz is used for the data transmission.
§Two oscillators used for the modulating frequency for load control.
§Two modulating frequency: 1.2 KHz and 10 KHz.
§2 KHz low pass and 10 KHz high pass filters in the transmitter for better
transmission and reduced noise level.
§A high frequency oscillator for generating the carrier frequency of 102 MHz.
§An antennae for the radio frequency transmission.
The Receiver Section
§FM receiver for the frequency demodulation.
§The two filters for distinguishing the two modulated signal.
§The logic circuit to make the load turn on and off with the same trigger i.e.
turn on the load with the high trigger and turn off with same other high level
trigger.
§Electromechanical devices to trigger the AC driven load.
The Transmitter Section
3.1.1 Oscillator
The oscillators used here are Wein Bridge Oscillators. The total phase shift around the circuit is zero degree. This condition occurs only when the bridge is balanced, i.e. at resonance. The transmitter section consists of the two oscillators for the modulating frequency of 1.2 KHz and 10 KHz.
1.2 Kiloherz Wein-bridze oscillator
Modulator
Fig 6 shows the carrier frequency generator and modulator. The modulation of the frequency is done by the modulating signal by changing the reactance of the tank circuit i.e the carrier oscillator. For the colpitt oscillator, the components at the input and output are connected in parallel. In this case, the feedback through the capacitor is negligible in comparison to that through the inductor.
The used antenna is the dipole antenna of the length λ/8. This propagates the radio frequency of 102 MHz to the receiver for the load control.
The Receiver Section
3.2.1 FM Demodulator
For the load control, the signal is demodulated in the receiver part. The work had been done for demodulating the signal but the appropriate output was not obtained. Thus for the demoduation the FM receiver is used which acts as a demodulator for the receiver section. A FM receiver can be used for this purpose as the main purpose is the demodulation only.
3.2.2 Filter
The filter in the receiver part separates the two frequency from the transmitter side. The filter used is the second order Sallen Key filter. The first Op-Amp used is the bandpass filter while the second opamp is for the low pass filter of 1.2 KHz.
Logic Circuit
The logic circuit consists of following circuits:
·Schmitt Trigger
·Monostable circuit
·Sequential circuit
The Schmitt trigger has the threshold frequency of + 2 volts. This is done in order to minimize the effect of noise. The output from the filter is fed into the schmitt trigger and the amplitude above 2V triggers the circuit. The negative going signal triggers the 555 monostable circuit and samples the signal to the NAND gate. The output of the NAND gate is the square wave. The negative going signal from the NAND gate triggers another 555 monostable circuit which in turn gives the signal to the JK Flip flop and thus controls the load.
Logic Circuit
The logic circuit consists of following circuits:
·Schmitt Trigger
·Monostable circuit
·Sequential circuit
The Schmitt trigger has the threshold frequency of + 2 volts. This is done in order to minimize the effect of noise. The output from the filter is fed into the schmitt trigger and the amplitude above 2V triggers the circuit. The negative going signal triggers the 555 monostable circuit and samples the signal to the NAND gate. The output of the NAND gate is the square wave. The negative going signal from the NAND gate triggers another 555 monostable circuit which in turn gives the signal to the JK Flip flop and thus controls the load.
The main purpose of the product (system) is the remote controller. It acts as a switch between the user and load in which the interfacing unit is the radio frequency lying in the FM band (88-108 MHz). The carrier frequency is of 102 MHz which is transmitted for the load control.
