Guide connect pc to tv
Guide to connect PC to TV via Scart socket.
connect pc to tv
connect pc to tv circuit
connect pc to tv circuit
connect pc to tv circuit
In particular, for use with the arcade game emulator Advance Mame
There is not much difference between TV and the arcade monitor. TV can be considered as an arcade monitor + TV tuner + audio amplifier in a plastic box. To use the TV as a monitor TV arcade should provide inputs for RGB video out of the arcade board, computer, etc. This is where input Scart come, not only accepts RGB video (0.7Vp-p @ 75ohms, but also has some useful control lines.
In order for the TV to accept video from a PC you must first:
1. Run the software and reduce the horizontal scan rate of ~ ~ 31khz to 15khz
2. Combining the horizontal and vertical synchronization signals to create a ‘composite video sync’ (0.3v/75 ohms).
3. Take high CVBS status line (10-12v) to enable input from pin 20 (composite video)
4. Take the high RGB status line (1-3v) to enable input from the pin 7, 11 and 15 (RGB)
Some of the TV can automatically switch the status line when the signal present themselves but most do not. Also, several TV will switch the CVBS only at 5v on CVBS status line but the majority require a full 12 volts.
Horizontal and vertical sync signals should be negative for the circuit to function (this is the default for AdvanceMame).
This series of ANDs two sync signals together using diode logic. H and V sync signals from the video card should be able to source / sink enough current for this circuit to operate properly. This is not a problem for any modern video card I have ever met, but maybe for older (ISA) cards. 11 of the pin VGA connector is connected to the ground to tell the computer that the color ‘monitor’ is connected (sometimes this pin is transferred to the ground in the connector).
During Boot protects TV
During boot of the PC video signal will be at a high frequency for the TV to handle. Feeding the TV signal will cause loss of sync and produce an unstable / rolling / duplicated images. Apart from that it can be annoying, in some cases, cause damage to the TV. To prevent the wrong signal reaches the TV, an Enable input has been added to both VGA> Scart circuit. This allows synchronization to be disabled during boot (or any other time H. frequency too high). There is also an RGB Scart input status to the socket that will empty screen when off. This is usually turned off the Enable line sync not stop the video appeared on the screen.
This circuit works like ‘Auto Enable me’ in detecting when the sync runs on a specific frequency (18.5kHz ± 10%). The circuit consists of two one-shots retriggerable. At each horizontal sync pulse is triggered and produces IC1A pulse 54μS. If H-sync is ~ 15kHz then 54μS will trigger IC1B every 64μS pulse. As set IC1B to 84μS, pulse comes in every continuous 64μS it retriggers, keeping output (Q) at the high logic. If H-sync rises above ~ 18.5kHz time between each sync pulse 54μS and falls below IC1A is constantly retriggered. The output of logic IC1A is high and because there was no pulse to trigger IC1B output is logic low.
Manufacturing Bastard! There does not seem 74xx123 standards out there, many of them use slightly different ‘K’ value of their time formula. The formula is TW = R * C * K (TW in seconds, R in ohms, C in farads). Check the table below for different K values along with the suggested value for R1/R2 parts differently. If the value of resistor is non-standard and series / parallel some resistors to get close, within 5% fine.
Utilizing the (usually) stereo amplifier on TV. To control the volume to work with both the volume on the TV and sound card should come up to them (or the loudest volume you want to go).
Construction
The first thing to do is find a cable with a VGA (HD15) connector is mounted, to cut the cable from an old monitor or VGA cable (cut off one end) is perfect. Sometimes there is enough space in the connector to the circuit, ie simple circuit can be transferred point to point on the Scart socket and Enable Parallel Port circuit will easily fit into a shell D25.
If more space is needed and then build a circuit on a board or prototype veroboard and mount into a small project box. Mount women Scart connector on the side and drill a hole for the wire to poke through. Something like …
I have designed a PCB for Improved VGA -> Scart + Switch PIC-based circuits small enough to go into space in a Scart plug. Most use surface mount components to achieve the small size. C1 and C2 is a tantalum type capacitor and an additional decoupling capacitor installed between the power and ground pins of the PIC.
In the old TV overscan can be reduced by adjusting the Horizontal / Vertical height is located in the control set. To make this new adjustment on the TV, enter the service mode and make the necessary adjustments with the remote control on the screen through the screen. Info on how to make this adjustment can be found in the TV service manual (you may need to rent / buy one).
