Jun 5, 2021

Bondwell 8 RGBi to Scart

Bondwell 8 is a nice little portable 8088 computer. It has a LCD screen with grayscale that isn't great for gaming. Since it has Composite and RGB ports I was curious to see if i could connect it to a TV. The composite port did only carry black and white signal so to get colour the RGB port was the only option.
 
I manage to find a pin out of the RGB port online. It turned out to be a standard RGBI port used for CGA/EGA graphics.

Since the signals are TTL level (5V) it has to be reduced to 700mV. Thes signals are digital and to produce more colors it has an intensity signal that needs to be combined with the RGB data. I made the circuit below to ha this. It is inspired by a design on H2Obsesion. I was a bit lazy so instead of combining hsync and vsync to composite sync I simply used the composite video output. Turns out that it works great!

I cut of a standard Scart cable that i zip tied to a prototype board with the circuit.
 

I started Pinball Magic in CGA mode and hey we got color!


Feb 10, 2021

Pong game RGB Mod

This console was made in Hong Kong and sold under many names like Grandstand, Soundic, Hanimex or as in my case MARK (Prelude Modell 64562).

My first attempt was to make a Composite video mod. This resulted in a horribly noisy video output. After some investigation I realized that it is easy to make an RGB mod for this console since it has separate signals for sync and the graphical elements. The signals are provide by the "AY-3-8610" chip in the cartridge. This is a single-chip-game that is called Supersportic or PC-501. It has 8 Pong style games and 2 that requires a rifle. I mapped the colors as close as possible to the original except for the background that I made black mostly because it was easier. But I think black is kind of cool. I may go back and add an option to make it green later. That would require a 3 input NOR gate...

Image captured from the console.

Below are some notes that may help if you are going to do a similar mod. I also removed the RF-modulator board and replace most of the capacitors. I accidentally blow up a 1N4148 diode before I realized that positive voltage from the external 9V PSU is ground for the circuits on the board! 

This is the result!

This Scart cable fit in the old RF output hole.
 
These are the connection point on the main PCB.

 
This is the schematic for my connections. The reason for using a 40106 schmitttrigger inverter was that it was what I had at hand. A regular inverter should do just fine. I had no OR gate chip so I used two schottky diodes.


Output amplifier and audio scaling.
 

Logic for color mapping.

 

 

Feb 6, 2021

Spectravideo 318/328 Burken Soft Index

Burken Soft Game Pac was a series of cassette releases of cracked games for the Spectravideo computers. Many of them are conversions of MSX games. Back in 2019 I made an index of the games in the collection that I posted on my Facebook page. I did this by taking screenshots of the menu found on the tape files. To make it more convenient to find them I re-post it here. I don't provide the cas files but you can easily find the by using a popular search engine... 

Intressting fact

"Burken" is slang for "the computer" in Swedish. The formal translation would be "the can" as in "the can of beans". 

1-12

13-24

25-29

Jan 30, 2021

RetroPie RGB Scart output with HDMI2VGA adapter

Running RetroPie  👍

Running RetroPie on CRT 😃

Running RetroPie on CRT with RGB 😍


VGA to RGB Scart cable

The RGB signals in VGA are compatible with the Scart RGB signals so they can be connect directly but the HSYNC and VSYNC must be converted to CSYNC. I used the circuit below for the conversion. The idea is taken from nexusuk.org that is no longer available but it can be accessed from archive.org.


To make the TV switch to RGB mode 5 volt should be feed via a 100 ohm resistor to pin 16 in the Scart connector. Normaly there is 5 volt output from a VGA port but this adapter don't provide that. Instead I came up with a solution to tap it from HSYNC. It's a bit ugly but it works fine for my setup. Another solution would be to connect a USB cable to the Raspberry Pi to get 5 Volts.


Change video mode for the HDMI port

To make it work we also need to edit the file config.txt in the boot partition.

1. Add these line to make text in dialogs and the console a suitable size.

framebuffer_width=1280
framebuffer_height=720


2. Add these line to output the correct signal for Scart RGB. Make sure that you don't have other video config line enabled!

hdmi_group=2
hdmi_mode=87

#60Hz
#hdmi_cvt=336 249 60 1 0 0 0

#50Hz
hdmi_cvt=320 312 50 1 0 0 0

You may want to adjust the numbers a bit for best result. For more details check this forum post


Enable audio from the 3.5mm Jack.

The VGA adapter did not have any audio output so I used the 3.5mm jack on the Raspberry Pi to feed audio in to the Scart connector. Run this command in a terminal to enable it:

sudo raspi-config

Select: Advanced Options-> Audio -> Force 3.5mm

Then reboot:

sudo reboot 


I managed to fit all parts inside the Scart connector!



Jan 3, 2021

Composite Video on Atari 2600 with an Amplifier

After some tinkering and simulation in LTSpice I ended up with the version of composite mod below. This is similar to the most common found online. This works fairly well on my CRT TV. It has a bit of noise but it is playable.

SIDE NOTE: I later realized that some of the electrolytic capacitors in the Atari 2600 had to be replaced. If you do this mod make sure to fix this also!

I also wanted to be able to connected it to my RetroTINK 2X Pro HDMI converter. I had problems with getting any image at all and when it worked the image was very dark.

I measured the amplitude from the signal and it was about 1/4 of the ideal level with a 75 ohm load. This is expected since this composite mod is an emitter follower and provides no amplification of the signal. The purpose is instead to be able to drive the 75 ohm impedance.

I came to the conclusion that the signal needs to be amplified. I took inspiration of some designs that I found online and made a spice model of my idea. After some iterations of testing and simulation I ended up with this design.


There are two potentiometers one for the DC/Sync pulse gain and one for AC Gain. I keep the composite mod in the console and conned this outside since it needs to be adjusted. Below is the final build. It is power with a USB adapter.

 
The images below are captured with a HDMI grabber from the RetroTINK 2X Pro.

 

The only issues is that the colors are slightly wrong when capturing the HDMI signal. But that can be adjusted with the capture software. The amplifier also removes a lot of the noise on the CRT. For the interested... here are some LTSpice simulation results that I saved.


Dec 15, 2020

Gamepad/Joystick in Wine (Ubuntu 20.04)

Configuring a Joystick or Joypad for Wine in Ubuntu 20.04 is pretty simple.

Start by installing the joystick tools:

    sudo apt-get install joystick 

If you have an analog controller it may need calibration:

    jscal -c /dev/input/js0 

Save calibration to file:

    jscal -p /dev/input/js0 > joystick1.cal

To load calibration later just source the file:

    source joystick1.cal

Start by checking that you controller works as expected in Wine by running:

    wine control

This will bring up the Wine Control Panel.



Lauch your game

    wine mygame.exe 

and locate the settings to map the controller.



Dec 14, 2020

Running Windows 3.1/95/98/XP Games in Linux

Most old Windows games that can't be run under Windows 10 will run well in modern Linux distributions like Ubuntu 20.04. You don't even need to bother with virtual machines like VirtualBox. All you need is Wine. Wine is an excellent Windows emulator that lets you run Windows application in Linux. Sounds complicated? Good new it is not! First you need to install Wine:

    sudo apt-get install wine

A nice feature is that you can run a game that was designed to run in full screen only in windowed mode. This is great if you want to record in OBS studio. To do this you need to run the Wine configuration tool. Start it by running:

    winecfg

Check Emulate a virtual desktop and press OK. This will make all Wine applications to run inside a window rather than on your Ubuntu desktop.To start a game just run:

    wine yourgame.exe

This will start you game in a new window. Most games will lock the mouse and keyboard inside this Window. To release it press Alt+Tab. If the game needs to be installed just run the installer with wine. The game can then be found in the Ubuntu Applications launcher. Happy gaming!


Contra Reloaded from ~2012