Skip to main content

Radio Band Position Display


This circuit is an add-on unit for radio receivers that lack band-position display. The circuit presented here can show up to nine bands. It also incorporates a novel feature to make the display dance (blink) with the audio level from the receiver. The power-supply for the circuit can also be derived from the radio-set. The conversion of selected channel to BCD format is achieved using diodes D1 through D15 in con-junction with resistors R4 to R7. The voltages developed across these resistors (R4 through R7) serve as logic in-puts to BCD inputs of BCD to 7-segment de-coder IC1 (CD4511).

Circuit diagram :

Radio Band Position Display Circuit Diagram

Radio Band Position Display Circuit Diagram

When all switches are in  ‘off’ state, the volt-age across resistors R4 through R7 is logic zero, but when any of the switches S1 through S9 is slided to  ‘on’ position, the output across these resistors changes to output proper BCD code to represent the selected channel. This BCD code is converted to 7-segment display by IC1. By this arrangement of diodes, the need for another decimal-to-BCD converter IC and associated parts is obviated. Switches S1 through S9 are actually parts of existing band-switch of the radio.

Usually, one or two changeover contacts would be found extra in the modular pushbutton-type band-switches of the radios. IC1’s display blanking pin 4 is connected to a display-blinker-control circuit wired around transistors T1 and T2. A small part of the audio signal from the speaker terminals is applied to rectifier diode D16 and filter capacitor C1 to pro-duce a pulsating DC across preset VR1. The sliding contact of preset VR1 is connected to the base of emitter-follower stage comprising transistor T2. The out-put of transistor T2, as amplified by transistor T1, is connected to pin 4 of IC1.Thus turning  ‘on’/‘off’ of display is con-trolled by the pulsating voltage developed from audio output of radio.

The power-supply regulator stage is needed only when radio power-supply is greater than 6V DC.

Author : M.K. Chandra Mouleeswaran Copyright : Electronic for you 2000


Labels:

Comments

Post a Comment

Popular posts from this blog

3 Channels Audio Splitter Amplifier Circuit Diagram using TL084

This is the schematic diagram of 3 channels audio splitter amplifier circuit which built using op-amp IC TL084. The 3 channels amplifier output distribution applies a single TL084.   3 Channels Audio Splitter Amplifier Circuit Diagram The very first step is to capacitive coupling having a p. 1.0 ~ electrolytic capacitor. The entries are railways Vee Y2 or 4.5 V. This enables working with an individual 9V power source. A voltage gain of 10 (1 M?/100 Kohm) is obtained in the first stage, as well as the other three floors are connected as a unity gain voltage followers. Every single output stage drives independently through an amplifier output 50 pF capacitor towards the resistance of 5.1 k ohm load. The response range is flat from 10 Hz to 30 kHz.
2 comments
Read more

RF amplifier protection

RF amplifier protection I have developed the protection circuit for the EB104 amplifier I am working on, after I finally had some time to design and test a few models. The main requirements have been: - protection in case of high temperature; - protection in case of high SWR; - protection in case of wrong output filter selection; - simple design (i’m a fan of the whole K.I.S.S. rule of thought), able to work in strong electromagnetic fields, reliable, inexpensive. Because i will be using the same directional coupler i have used in the SWR meter (the one made on PCB) wich is directly influenced by the signal frequency, and because i want full HF coverage, i cannot just measure the reflected signal and make a circuit cut the amplifier when it goes over a limit; on 28Mhz the coupler generates roughly 4 times more voltage that let’s say in 7Mhz. So a system that compares direct and reflected signal and triggers when the latter is percentually too high was needed, therefore an operational a...
Post a Comment
Read more

Simple Automatic Street Light

There have been lot of problems in street lights. Major problem in some places is every evening a person has to come and switch ON the street light and it should be again switched off in morning. Yes, this may not be the situation in everywhere but exists in many places. So this problem can be overcome by using a simple circuit. Below shown circuit will be automatically switched ON and OFF during night and morning times respectively. Circuit diagram : Simple Automatic street light Circuit Diagram In above circuit R1 can be used to adjust the sensitivity. And the working of the circuit is very simple. The LDR will have very low resistance during day time so the transistor Q1 will be in OFF condition. And during night time the resistance will be very high so automatically the transistor Q1 will be ON. The Q1 is PNP transistor and the emitter of Q1 is given to base of Q2. So the Q2 transistor will be ON only if the transistor Q1 is ON. The TRIAC is used in the circuit to make is circ...
Post a Comment
Read more