Electronica Stuff.blogspot.com: 2011

Telephone operated remote

Galaxy 9:39 AM

Telephone Operated Remote

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.

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.

FM remote Encoder/Decoder

Remote Circuits

Galaxy 9:30 AM

FM remote Encoder/Decoder

Description.

Here is the circuit diagram of an FM remote encoder/decoder using the ICs RF600E and RF600D. These devices are designed to provide a high level of security and operates from anything between 2 to 6.6V DC. Various electronic circuits like remote control systems, remote alarm systems, anti theft alarms etc can be implemented using the RF600E/RF600D pair.

The remote systems given here uses FM for the transmission. IC1 RF600E and its associated components form the encoder circuit. Pins 1 to 4 forms the switch inputs of IC1. When each push button switch is pressed a corresponding code will be generated at the pin 6 which is the data output pin. The encoded signal available at pin 6 is buffered using the transistor Q1 and the fed to the input of a general purpose FM transmitter module (M1). Such FM transmitter modules are very common in the market now.

The decoder system comprises of the IC2 RF600D and its associated components. Pins 17, 18, 1 and 2 are the digital data output pins of RF600D corresponding to the input switches S1 to S4 of the encoder/transmitter circuits. The digital data output pins 17,18,1 and 2 are asserted low when the relevant inputs S1 to S4 on the IC2 RF600E are asserted. M2 is a general purpose FM receiver module which receives the transmitted code and feds it to the data input (pin 9) of the IC2. Switch S1 can be used to select between latching and momentary digital output function. In latching mode digital output pins (OP1 to OP4) are only asserted for the corresponding transmit signal. In latching mode the output state is changed on each corresponding transmit signal. The learn switch S5 is used to enter the decoder IC in to the “learn mode”. Learn operation using push button switch S5 is as follows. 1) Press and release the push button switch S5. 2) The status LED D2 will glow when S5 is pressed and will remain ON when S5 is released. 3) Operate the encoder/transmitter once. 4) The status LED D2 will become OFF. 5) Operate the encoder/transmitter again. 6) The status LED will start flashing. 7) When the flashing of status LED stops, the encoder will be successfully taught to the decoder and the transmitter/encoder will now operate the receiver/decoder system. Up to seven encoder/transmitters can be learnt to each RF600D.Pin 3 of IC2 is the transmitter low battery indicator output and pin 11 is the serial data output.

Notes.

* Assemble the circuit on a good quality PCB.

* The ICs can be operated from anything between 2V to 6.6V.

* Switches S1 to S5 are miniature push button switches.

* S6 can be a miniature two way switch.

* Transmit LED D1 will glow whenever the encoder is transmitting.

* The power supply must be properly regulated and ripple free.

* I recommend using batteries for powering the circuit.

* Go through the datasheets of RF600E and RF600D before attempting this circuit.

Ding-Dong sound generator

Sound Circuits

Galaxy 12:29 PM

Ding-Dong sound generator

Description.

This is the circuit diagram of a ding dong sound generator based on two NE555 timer ICs.The circuit is designed to toggle between two adjustable frequencies to produce the ding dong sound. The first NE555 (IC1) is wires as an astable multivibrator operating at 1Hz. The frequency of the second NE555 (IC2) is modulated by the output from the first IC. This is attained by connecting the output of first IC to the control pin (pin5) of the second IC. The tone of the sound depends on the frequency of the second IC and the changeover time depends on the frequency of the first IC.

Notes.

* The circuit can be assembled on a Vero board.

* Use 9V PP3 battery for powering the circuit.

* POT R4 can be used to adjust the tone of the sound.

* POT R2 can be used to adjust the change over time.

* IC1 and IC2 must be mounted on holders.

* K1 can be a 8 ohms, 1/2 watt tweeter

USB Lamp circuit

USB Circuits

Galaxy 12:20 PM

USB Lamp Circuit

Description.

Here is a simple USB powered lamp that can be used to light your desktop during power failures. The circuit operates from the 5 V available from the USB port.The 5V from the USB port is passed through current limiting resistor R2 and transistor Q1. The base of transistor Q1 is grounded via R1 which provides a constant bias voltage for Q1 together with D2.The diode D1 prevents the reverse flow of current from battery.C1 is used as a noise filter.Two white LED’s are used here for the lamp, you can also use a 2 V torch bulb instead of LED’s. LED D3 indicates connection with USB port.

Notes.

* USB port is only able to provide up to 100 mA current.So don’t overload the circuit with more no of LED’s.

* Before wiring the circuit confirm the positive and ground leads of USB by a multimeter.

* Switch S1 can be used to turn on the lamp.

USB sound card

USB Circuits

Galaxy 12:04 PM

USB sound card

Description.

Designing and building a USB sound card is no longer a head ache because we have got the PCM 2702 integrated circuit from Texas Instruments. The PCM2702 is an integrated 16 bit digital to analog converter that has two digital to analog output channels. The integrated interface controller of PCM2702 is compliant to the USB 1.0 standards. The IC can handle sampling rates of 48 KHz, 44.1 KHz and 32 KHz. The IC also has a number of useful features like on-chip clock generator, digital attenuator, play back flag, suspend flag, zero flag, mute function etc. The most interesting thing is that this circuit is plug & play and doesn’t need any driver software for Windows XP and Windows Vista operating systems.

The circuit gets control data and audio data from the USB through the D+ and D- pins of the PCM2702 all the data transferring is carried out at full speed. The decoded audio signals will be available at the VOUTL and VOUTR pins of the IC. The 12MHz crystal is connected between the XT0 and XT1 pins of the IC. The VBUS (USB bus power) pin and DGND (digital ground) pins of the IC are connected to the +5V and ground pins of the USB respectively. The circuit requires +5V DC and +3.3V DC for operation and both of these voltages can be derived from the USB port using LDO (low drop out) voltage regulators (not shown in circuit).

Block diagram of PCM2702.

Notes.

* +5V DC supply can be derived from the USB port using a +5V LDO regulator.

* +3.3V DC supply can be derived from the USB port using a +3.3V LDO regulator.

* Audio signals (output) available at VOUTL and VOUTR requires further amplification for driving low impedance head phones or loud speakers.

* The PCM2702 is available only in SSOP28 package and requires special care while assembling.

* Before attempting this circuit please go through the datasheet of PCM2702 and get a clear idea about the device.

AM receiver using ZN414

Radio Receiver

Galaxy 10:15 AM

AM receiver using ZN414

Description.

This is the circuit diagram of the simplest single chip AM radio. The circuit is designed around the IC ZN414Z which is a ten transistor tuned radio frequency receiver .The IC has only three leads and is available in the TO92 package. All necessary circuits required for an AM receiver (RF amplifier, detector and AGC are incorporated inside the IC ).In the circuit given below, capacitor C1 and resistor R1 forms the tank circuit which is essential for tuning. Capacitor C4 decouples DC from the output of the IC and C1 bye-passes the noise. Transistor Q1 and associated components forms a classic driver stage for the headphone. Head phone is connected across the resistor R5 and R4 gives necessary biasing for the transistor Q1.

Notes.

* Assemble the circuit on a good quality PCB.

* The circuit can be powered from a 1.5V cell.

* Do not give more than 1.8V to the circuit as it will destroy the IC.

* For L1 make 80 turns of 0.3mm enameled copper wire on a 5cm long ferrite rod.

* K1 can be a high impedance crystal earpiece.

Police siren using NE555

Sound Circuits

Galaxy 9:30 AM

Police siren using NE555

Description.

A lot of electronic circuits using NE555 timer IC are already published here and this is just another one.Here is the circuit diagram of a police siren based on NE55 timer IC. The circuit uses two NE555 timers ICs and each of them are wired as astable multivibrators.The circuit can be powered from anything between 6 to 15V DC and is fairly loud.By connecting an additional power amplifier at the output you can further increase the loudness.

IC1 is wired as a slow astable multivibrator operating at around 20Hz @ 50% duty cycle and IC2 is wired as fast astable multivibrator operating at around 600Hz.The output of first astable mutivibrator is connected to the control voltage input (pin5) of IC2. This makes the output of IC2 modulated by the output frequency of IC1, giving a siren effect. In simple words, the output frequency of IC2 is controlled by the output of IC1.

Notes.

* The circuit can be assembled on a Perf board.

* I used 12V DC for powering the circuit.

* Instead of using two NE55 timer ICs, you can also use a single NE556 timer.

* NE556 is nothing but two NE555 ICs in one package.

* Refer the datasheets of NE555 and NE556 to have a clear idea.

* Speaker can be a 64ohm, 500mW one.

2 km FM transmitter

Radio Transmitter FM

Galaxy 8:38 AM

2 km FM transmitter

Description.

With a matching antenna, the FM transmitter circuit shown here can transmit signals up to a range of 2 kilo meters. The transistor Q1 and Q2 forms a classic high sensitive preamplifier stage. The audio signal to be transmitted is coupled to the base of Q1 through capacitor C2. R1, R3, R4, R6, R5 and R9 are the biasing resistors for the preamplifier stage comprising of Q1 and Q2. Transistor Q3 performs the collective job of oscillator, mixer and final power amplifier.C9 and L1 forms the tank circuit which is essential for creating oscillations. Inductor L2 couples the FM signal to the antenna.

Notes.

* Assemble the circuit on a good quality PCB.

* The circuit can be powered from anything between 9 to 24V DC.

* Inductor L3 can be a VK220J type RFC.

* For L1 make 3 turns of 1mm enamelled copper wire on a 10mm diameter plastic former. On the same core make 2 turns of 1 mm enamelled copper wire close to L3 and that will be L2.

* Frequency can be adjusted by varying C9.

* R9 can be used to adjust the gain.

* For optimum performance, value of C8 must be also adjusted.

* Using a battery for powering the circuit will reduce noise.

Single Chip FM Radio circuit

Radio Receiver

Galaxy 8:37 AM

Single Chip FM Radio circuit

Description.

Here is a compact low cost FM radio circuit using IC7400. This circuit is designed as per the data sheet and the result is excellent.Ideal for all category of electronic enthusiasts.

The TDA7000 is a monolithic integrated circuit for mono FM portable radios, where a minimum on peripheral components is crucial. The IC TDA 7000 has a Frequency-Locked-Loop system with an intermediate frequency of 70 kHz. The intermediate frequency selectivity is achieved by active RC filters. The only function which needs alignment is the resonant circuit for the oscillator, thus selecting the reception frequency. Spurious reception is avoided by means of a mute circuit, which also eliminates too noisy input signals. Special steps are taken to meet the radiation requirements.

Notes

* For L1 and L2 wind 5 turns of 0.6 mm enameled Copper wire on a 4 mm dia plastic former.

* For antenna use a 50mm long insulated copper wire.

* IC TDA 7000 can withstand up to 10 V supply voltage.But I recommend 6V.

* Use an 8 Ohm speaker or Headphone at the audio output.