Description.
The circuit given below is of a telephone operated DTMF remote. The circuit can be used to switch up to 9 devices using the keys 0 to 9 of the telephone. Digit 0 is used to switch the telephone system between remote switching mode and normal conversation mode. IC KT3170 (DTMF to BCD decoder) is used to decode the DTMF signals transmitted over the telephone line to corresponding BCD format. IC 74154 ( 4 to 16 demultiplexer) and IC CD4023 (dual D flip flop) is used to switch the device according to the receive DTMF signal.
The operation of the circuit is as follows. After hearing the ringtone from the phone at receiver end, press the 0 button of the remote phone. The IC1 will decode this as 1010.The pin 11 of IC2 will go low and after inversion by the NOT gate in IC3 it will be high. This will toggle the flip flop IC5a and the transistor Q1 will be switched on. This will make the relay K1 ON. The two contacts C1 and C2 of the relay K1 will be closed. C1 will form a 220 Ohm loop across the telephone line in order to disconnect the ringer from the telephone line (this condition is similar to taking the telephone receiver off hook).C2 will connect a 10KHz audio source to the telephone line in order to inform you that the system is now in the remote switch mode. Now if you press 1 on the transmitter phone, the IC1 will decode it as 0001 and the pin 2 of IC2 will go low. After inversion by the corresponding NOT gate inside IC3, it will be high. This will toggle flip flop IC5b and transistor Q2 will be switched ON. The relay will be energized and the device connected through its contacts gets switched. Pressing the 1 again will toggle the state of device. In the same ways Keys 2 to 9 on the transmitter phone can be used to toggle the state of the device connected to the channels O2 to O9. After switching is over, press the O key on the transmitter phone in order to toggle the flip flop IC5a to de-energize the relay K1.The 200 Ohm loop will be disconnected from the line, the 10 KHz audio source will be removed and the telephone receiver will be ready to receive new calls.
Circuit diagram.

Notes.

• Assemble the circuit on a good quality PCB.
• Use 6V DC for powering the circuit.
• A simple NE555 based oscillator can be used as the 10 KHz audio source.
• All IC’s must be mounted on holders.
• The section drawn in red must be repeated eight times (not shown in circuit).
• In certain countries circuits like this cannot be connected to telephone line.I do not have any responsibility on the legal issues .

IC’s used in this project.
KT3170
The IC KT 3170 used here is a low power DTMF receiver IC from Samsung. The IC is fabricated using low power CMOS technology and can detect all the 16 standard DTMF tones. The DTMF signal received will be decoded to a BCD output for switching applications.
74154
74154 is a 4 line to 16 line decoder from national semiconductors. It decodes a 4 bit input code into one of 16 mutually exclusive outputs. Maximum supply voltage is 7V and normal power dissipation is around 175mW.
CD4049
CD4049 is a CMOS hex inverter from Texas Instruments. Each of the IC contains six NOT gates. Maximum supply voltage possible is 20V and each gate can drive up to two TTL loads.
CD4013
CD4013 is a CMOS dual D filp flop. Each flip flop has independent data, reset Q, Qbar, clock and set pins. The maximum possible supply voltage is 15V and the IC has high noise immunity.

Description.
Here is the circuit diagram of simple but highly effective TV remote jammer circuit. Most of the TV remotes have 38KHz operating frequency. A flood of IR beams in the same frequency can easily confuse the TV receiver and this is the operating principle of our jammer. The circuit is nothing but an astable multivibrator based on NE555 IC. The output of NE555 is amplified using a PNP transistor SK100 to drive the IR LEDs. Not only TV remotes, but any IR remotes operating in the 38KHz frequency region can be also jammed by using this circuit.

Circuit diagram.

Notes.

• The circuit can be assembled on a Vero board.
• Use a 9V PP3 battery for powering the circuit.
• Mount the IC on a holder.
• POT R4 can be adjusted to exactly match the jammer’s frequency to the remotes frequency. This adjustment is very essential for effective jamming.

Description.

A different type of remote control circuit employing ultrasonic signals is given here.

The transmitter part of the circuit is build around IC1(NE 555).The IC1 is wired as an astable multi vibrator operating at 40KHz.The output of IC1 is amplifier the complementary pair of transistors ( Q1 & Q2) and transmitted by the ultrasonic transmitter K1.The push button switch S1 is used the activate the transmitter.

The receiver uses an ultrasonic sensor transducer (K2) to sense the ultrasonic signals. When an ultrasonic signal is falling on the sensor, it produces a proportional voltage signal at its output. This weak signal is amplified by the two stage amplifier circuit comprising of transistors Q3 and Q4.The output of the amplifier is rectified by the diodes D3 & D4.The rectified signal is given to the inverting input of the opamp which is wired as a comparator. When ever there is an ultrasonic signal falling on the receiver, the output of the comparator activates the transistors Q5 & Q6 to drive the relay. In this way the load connected via the relay can be switched. The diode D5 is used as a free wheeling diode.

Circuit diagram with Parts list.

Notes.

• Assemble the the circuit on good quality boards.
• The switch S1 can be a push button switch.
• The ICs must be mounted on holders.
• The transmitter can be powered from a 9V PP3 battery.
• For low power applications the receiver can be also powered from a 9V PP3 battery.For high power applications, use a  9V DC power supply.
• The preset R16 can be used to adjust the sensitivity of the receiver.
• The frequency of the ultrasonic signal can be varied by adjusting the preset R17.Adjust it for optimum performance.

Description.

Here is a versatile remote controlled appliance switch that can ON or OFF any appliance connected to it using a TV remote.

IR remote sensor IC TSOP 1738 is used for recieving the signal. Normally when no signal is falling on IC3 the output of it will be high.This makes Q1 OFF.When a signal of 38 KHz from the TV remote falls on the IC3 its output goes low.This makes Q1 conduct and a negative pulse is obtained at pin 2 of IC 1  NE 555.Due to this IC1 wired as a monostable multivibrator produces a 4 Sec  long high signal at its out put.This high out put is the clock for IC 2 which is wired as a Flipflop and of , its two outputs pin 3 goes low and pin 2 goes high.The high output at pin 2 is amplified to drive the relay .For the next signal  the outputs of IC2 toggles state. Result, we get a relay toggling on each press on the remote.Any appliance connected to this circuit can be switched ON or OFF.

Circuit Diagram with Parts List .

Notes.

• Before wiring the circuit make sure that the carrier frequency  of the TV remote you have is 38 KHz.For that wire the sensor part only ,point your remote to the TSOP1738 and press any switch.If  out put of TSOP1738  goes  low them ok, your remote is of 38Khz type.Nothing to worry almost all TV remote are of this type.
• You can use any switch because for any switch the code only changes,the carrier frequency remains same.We need this carrier frequency only.
• Assemble the circuit on a good quality PCB or common board.
• The appliance can be connected through NO or NC  and contacts of the relay .

Description.

This circuit was designed in response to a request from my reader. What he asked for was a 1KHz IR transmitter circuit for some remote control application. I think this circuit may satisfy him. Any way this circuit can be used where ever a low power IR transmitter of 1 KHz operating frequency is needed. This transmitter can transmit up to a distance of about 10 meters.

The circuit is based on a NE555 timer IC (IC1) which is wires as an astable multivibrator to produce 1KHz pulses. The output pulses of the IC1 will be amplified by the Q1(SK100) to drive the two IR transmitter LEDs wired serially. The resistors R1, R2 and capacitor C2 determines the operating frequency of the IC.The circuit starts emitting IR pulses when ever the push button switch S1 is pressed.

Circuit diagram with Parts list.

Notes.

• The circuit can be powered from a 9V PP3 battery.
• The switch S1 is a push button type switch.
• The IC 1 must be mounted on a holder.