Replica 40x25 VDU (Teletext) Interface Board 

Based on the issue 4 schematic and the layout from my own issue 3 board.

Preset R3 is adjusted to get a 6MHz clock at IC3 pin 8.

Note: this board will only compatible with a 1MHz CPU (either 6502 or 6502A Board) because the 6MHz clock is derived from a 1MHz Ø2 (it may be possible to tweak the VCO for 2MHz but I haven't tried).

No links need to be fitted or changed.

I have fitted a 6-pin DIN socket for the RGB output wired as per the BBC computer RGB socket.

Connections to J1 are then wired as follows:

• pin 1 Light pen 0V

• Pin 2 Light pen signal

• Pin 3 Light pen +5V

• Pin 6 Composite Sync to DIN Pin 4

• Pin 8 0V to DIN Pin 5

• Pin 10 Blue to DIN Pin 3

• Pin 11 Green to DIN Pin 2

• Pin 12 Red to DIN Pin 1

• Pin 13 +5V to DIN Pin 6

• Pin 14 0V to BNC ground

• Pin 15 Composite Video to BNC signal

Schematic

• 40x25 VDU (Teletext) Interface Board Schematic

Bill Of Materials

• 40x25 VDU (Teletext) Interface Board BOM

Front Panel Drilling

• 40x25 VDU (Teletext) Interface Board Front Panel

Blank PCB

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