Radio Band Position Display

This circuit is an add-on unit for radio receivers that lack band-position show. The circuit offered right here can express up to nine bands. It additionally contains a novel characteristic to make the show dance (blink) with the audio level from the receiver. The power-supply for the circuit will additionally be derived from the radio-set. The conversion of selected channel to BCD format is achieved the usage of diodes D1 via D15 in con-junction with resistors R4 to R7. The voltages developed across these resistors (R4 via R7) function good judgment in-puts to BCD inputs of BCD to 7-segment de-coder IC1 (CD4511).

Circuit diagram :

Radio Band Position Display Circuit Diagram

When all switches are in  ‘off’ state, the volt-age throughout resistors R4 via R7 is good judgment zero, however when any of the switches S1 via S9 is slided to  ‘on’ position, the output throughout these resistors modifications to output correct BCD code to symbolize the selected channel. This BCD code is transformed to 7-segment display by IC1. By this association of diodes, the need for another decimal-to-BCD converter IC and associated phases is obviated. Switches S1 via S9 are in fact sections of existing band-switch of the radio. 

Usually, one or two changeover contacts could be discovered further in the modular pushbutton-type band-switches of the radios. IC1’s show blanking pin 4 is hooked up to a display-blinker-control circuit wired around transistors T1 and T2. A small part of the audio sign from the speaker terminals is utilized to rectifier diode D16 and filter capacitor C1 to pro-duce a pulsating DC throughout preset VR1. The sliding contact of preset VR1 is attached to the base of emitter-follower stage comprising transistor T2. The out-put of transistor T2, as amplified with the support of transistor T1, is attached to pin four of IC1.Thus turning  ‘on’/‘off’ of show is con-trolled with the aid of the pulsating voltage developed from audio output of radio.

The power-supply regulator stage is required best when radio power-supply is greater than 6V DC.

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