Electronica Stuff.blogspot.com: September 2011

AM receiver using ZN414

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.