OveRGBkill is an expandable analog RGB video switcher using common components.
This is all hobbyist hardware and software, and could potentially damage your precious retro gaming equipment. It is provided "as is", without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose, and noninfringement.
Be sure to scroll down for important notes integrating this into a real world AV system.
- 5, 10, or 15 RGB inputs
- Standard Megadrive (MD2) style Mini-DIN 9 connectors
- Sense and automatically switch to active input
- Uses composite for sync
- Routes R, G, B, composite/sync, stereo audio L, R, ground, and +5V. Other pins are not connected.
Pairs well with a RGB-Component transcoder if you have a TV with component input.
Some notes on how to wire your consoles for RGB output, from my experience. A good starting point is RetroRGB.
For systems that are already RGB capable but don't have an MD2 connector, such as Saturn, SNES, N64, Playstation 1/2, etc., I'll make an MD2 connector out of a SCART connector:
- Purchase an RGB-capable SCART connector
- Splice off the SCART head
- Disassemble the SCART head and use a SCART pinout to note which colour wire has which purpose. Many I've bought from AliExpress have this pinout but you must verify for yourself
- Yellow — Composite
- Orange — Red
- Green — Green
- Blue — Blue
- Brown — +5V
- Purple — GND
- Black — Audio GND
- White — Audio Left
- Red — Audio Right
- Use a Mini DIN-9 breakout PCB with a female Mini DIN-9 socket
- For simple applications, something like MobiusStripTech's breakout is great
- To include AC coupling capacitors, voltage dividers and/or mono expansion, use the breakout PCB in this repository!
- A 3d printable shell finishes the cable. On one end you have a console-specific connector, on the other end you have a female MD2 connector, and use a straight Mini DIN-9 cable to wire this to your switcher.
- For the MobiusStripTech breakout, this case works well
- If using our breakout PCB, an accompanying shell is here, based on sensorslot's project box template
Needs 220μF coupling capacitors on RGBC, use the breakout PCB in this repository
Needs 220μF coupling capacitors on RGBC, use the breakout PCB in this repository
Seems to use a much higher voltage, incorporate a voltage divider of around 1:2 on RGBC (for example R1=33Ω, R2=75Ω), using the breakout PCB or the customizable daughterboard.
Many of these use 5V TTL CSYNC, incorporate a voltage divider of around 1:4 on C using the breakout PCB or the customizable daughterboard.
In general, if you have RGB modded your system, well designed mods will already use the correct voltages, AC coupling, and impedances, and I found that my RGB-modded PC Engine (doujindance) and NESRGB needed no further modification.
Note In fact it probably never hurts to add 220μF coupling capacitors on all inputs. This could be incorporated into future revisions of the daughterboard.
Use the simple daughterboard if your inputs are standardized: if they're all AC-coupled (0 DC bias), with 75Ω impedance, and 0.7V peak-peak at 100 IRE.
You may use the customizable daughterboard to adjust voltages with voltage dividers built into the board. Or it may be more convenient to build these into your cables. It's your choice.
Of course you can also mix and match.
The TI 74HC4067 muxer has On-On resistance of around 230Ω. If you use this with an impedance-matched source designed for 75Ω termination, this means that there will be 75+230=305Ω resistance inline, and 75Ω termination. This forms a voltage divider that will make the image much more dim (normally the 75Ω inline and 75Ω terminating resistors form a 1:2 divider).
If you have control over the termination, for example by using any buffered video device between the switcher and your TV, you can design around this. For example, if using a RGB-Component transcoder, replace the 75Ω terminating resistors with ~300Ω resistors.
If you don't need to use a transcoder, you could instead use a simple THS7374 circuit with 300Ω termination.
Note there are multiplexers with much less resistance that could be used instead, to easily alleviate the issue. Since I had control over the circuit after the switcher, I chose to use this low-cost multiplexer and solve for the additional resistance.
Note alternatively, a video buffer could be integrated into a future revision of the hardware so that the switcher has typical 75Ω impedance.
In the MD2 pinout, ground is carried over the shielding of a cable. Therefore, all mini-DIN 9 cables used with this must be shielded. Some cheap cables you may find on AliExpress skimp out on this, and it's not called out, so beware. Use a multimeter to check continuity between the metal outer ring of each end of the cable to verify you have shielded cables.
I can verify that (at the time I purchased them) these cables from "wg cable store" are shielded: AliExpress