I have some experience with electronics, but no experience with AV. I would love to learn how to do something like the following:

I want to build a little circuit which will do the following:

        Input a SCART(RGB signal) and a Composite RCA connection.
        Output SCART(RGB signal - passthrough of whatever signal comes in 
        over the Input SCART - or Composite over scart from the composite RCA connection)
        Switch when flicked left outputs the SCART signal coming in, 
        when flicked right outputs the Composite signal.

My circuit would have a switch which when flicked to the left does a SCART passthrough, when flicked to the right, it flows the composite signal over the SCART output as per the following diagram:

enter image description here

I have a couple of questions to help me solve this problem:

  • I need to know the name of the SCART IN, Composite In breakout board type connector for my circuit
  • How might the switch circuitry be designed

Help in these areas would help give me a starting point of actually building my little circuit!

  • \$\begingroup\$ What kind of SCART signal are you handling? \$\endgroup\$
    – Majenko
    Sep 1 '16 at 15:11
  • \$\begingroup\$ RGB scart will be the input coming in....going out should just be a mirror of the signal coming in, or composite over SCART. \$\endgroup\$ Sep 1 '16 at 15:17

Small signal relays might be your simplest and cleanest choice here. Reed relays might be an ideal selection.

Selecting double-throw relays makes wiring the system easy - four relays in parallel powered by the same switch. When all are on three route the RGB signal to the output, and the fourth routes the composite nowhere. When all are off three route the RGB signal nowhere, and the fourth routes the composite signal to the output.


simulate this circuit – Schematic created using CircuitLab

Add more relays to switch more signals as you see fit. You may want to switch the grounds separately, or you may want to join them all together for simplicity. Replacing individual relays with DPDT (Dual Pole Double Throw) would also reduce part count, but these tend to be more available for larger power switching, not small signals.

As for connectors, you will find what you want by dismantling an old VCR.

  • \$\begingroup\$ This looks really good - love the look of it. Can you help me source these particular parts...im not sure what they are such as those relays....which would be a good choices. Additionally, what about the other 19 pins of SCART RGB, like CSYNC etc im assuming I would need to route them through also? \$\endgroup\$ Sep 1 '16 at 15:43
  • \$\begingroup\$ Anything you need to route for your setup you need to add a relay for. What relays you choose depends on your power supply voltage. They typically come in 5V, 12V and 24V varieties. For example: tinyurl.com/z6a7ldw \$\endgroup\$
    – Majenko
    Sep 1 '16 at 15:51
  • \$\begingroup\$ Power source would be a normal 110 / 220v connector, so whatever would be needed to receive this input, and step it down to 5v / 12v / 24v....? \$\endgroup\$ Sep 1 '16 at 15:59
  • \$\begingroup\$ Some kind of power supply is in order then. Maybe a phone charger (5V) would be ideal? \$\endgroup\$
    – Majenko
    Sep 1 '16 at 15:59
  • \$\begingroup\$ That sounds ideal! Good idea. So can you help expand out this circuit to include this bit. I am struggling to see how the relay switch is flowing appropriate signals to the relay - is there a way I can see the behaviour of flicking the switch on this CircuitLab circuit? \$\endgroup\$ Sep 1 '16 at 16:03

It would be CONN, SCART, Female, thru-hole PCB mount SCART 21 pin https://en.m.wikipedia.org/wiki/SCART

However the square posts may damage if using a plugin proto plug, so solder short resistor wires as pins using 1/4w and cut to length 3mm to have a round connection.

However, these connectors are not common and mostly IDC ribbon interface.


To MUX RGB, ground and Composite Video , I assume you already understand the interface pins.

  • \$\begingroup\$ can you give more of a circuit plan for the use case so I can learn the components, and their role in this application? This would aid my learning a huge amount. \$\endgroup\$ Sep 2 '16 at 2:09

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