Arcam AV8 Refer to circuit diagram L898 sheet Introduction, Power Supply, LEDs, Remote receiver

AV8 Display Board

Refer to circuit diagram L898 sheet 1

Introduction

The AV8 display board contains the front panel graphical VFD display module, buttons, LEDs, remote IR receiver and encoder.

The graphical VFD display receives data directly from the micro on the digital board (via SK100).

Power Supply

The supply rails are supplied to the Display PCB Via SK100 from the digital board.

Please note that the supply rail marked P36VF1 has been reset to a voltage of +21volts, this is because the display was found to be to bright when supplied with +36volts.

LEDs

These are driven using two 74HCT595 (IC101 and IC102) output latches controlled via SK100 by the micro on the digital board.

!LED 100 is a bi-colour LED and is used for standby.

!LED 101 to LED 110 are function and source indicators.

Remote receiver

The remote receiver (RX101) output is buffered via a 74HC14D (IC104) this is then connected to the digital board via SK100 pin15.

Volume/encoder

The encoder (SW124) output A and B is buffered via a 74HC14D (IC104) as PHASE A and PHASE B to the digital board via SK100 pins 12,13.

Keyboard

The keyboard is polled using a 74HCT595 (IC100), this is controlled by the micro on the digital board which scans the keyboard output.

Scanning sequence:

!The outputs of IC100 Q0 to Q7 are set low in sequence

!The keyboard lines KB0, KB1 and KB2 are read

When a key is pressed it will result in a low on KB0, KB1 or KB2.

The micro knows which output has been polled low (IC100 Q0 to Q7) and which line is low KB0, KB1 or KB2 and therefore the intersecting point will represent the key which has been pressed e.g. Q2 is polled low and KB1 is read as low means that the “CD” button has been pressed.