Video is brought into the interface card by connecting a standard 15 way high density (HD) monitor cable between the PC  and 15 way HD PCB socket (SK1).

The video signals are taken out on the JAMMA loom PCB edge connector, pins 12 (red), 13 (blue), 14 (gnd), N (green) and P (composite).

The monitor switching is controlled by connecting a standard PC 25 way printer lead between your PC's printer port and connector SK4 on the interface card PCB.

The +5v power for this circuit comes from the JAMMA loom.

Composite Out

An Arcade monitor requires composite sync to operate and a PC graphics card normally supplies separate horizontal and vertical sync.  The circuit which consists of R3, R4, C2, C9 and IC1 combines the horizontal and vertical sync to produce the require composite sync.  This circuit was taken directly from the Hut web site.  Go there to check out how it works.

Signal Switching

This circuit is based on Brian Lewis' original design with a few of my own tweaks.  It relies on ArcadeOS sending bit 7 high on your PC's printer port to turn the Arcade monitor on.  

The method used here is to switch the RGB & sync lines on, not the mains power to the arcade monitor.  This means that there is no messing around with dangerous voltages inside your Cabinet.  The 4066 bi-lateral switches (IC2) provide the switching.  The track routing around these devices is quite critical so there is plenty of ground plane (0V) on the top and bottom of the PCB to reduce noise and crosstalk.

Enabling the switches (IC2) is done by a simple and cheap 7474 dual flip-flop (IC4) which has its initial state preset by the power-on-reset circuit consisting of IC7, C22 & R11.  The time constant produced by C22 and R11 is about 200 - 300 milli-seconds and is plenty to ensure correct operation.

R5 and LED1 are used to indicate the Arcade monitor status (on/off).

Important!

The video circuit in this project relies on bit 7 going high on the printer port of the PC which is normally done by the ArcadeOS software.  However, some PC motherboards send a hardware reset to the printer port on boot up which has the same effect.  If this happens then your Arcade monitor could possible be turned on before the correct screen refresh rate and resolution have been set and damage to the monitor could result!

In order to protect against this, LK6 enables you to choose between switching the monitor on the first or second time the printer port goes high.  If your PC sends a hardware reset on boot up, or if you are not sure, then set the jumper LK6 to pins 1 & 2.  If your PC does not send the hardware reset then just set LK6 to pins 2 & 3.  If you weren't sure and your Arcade monitor did not come on then try pins 2 & 3 (make sure you power down first).

Copyright 2000/2001.
You can email me at: ZangTumbTumb@freeUK.com.
Last updated: August 23, 2001.