Project files: Universal selectors (part 1)

This is the first in a series of posts for relay-based input (or output) selector boards made to be as universal as I could reasonably make them. This is part one, the selector boards themselves. Part 2 (which is coming shortly) includes the matching control boards (button-based and rotary switch) and an LED indicator board. There might eventually be a part 3 (and 4) as well to cover some additional variants and accessories.

What is it?
A relay-based selector boards with four single-ended inputs (or outputs). There are four board sizes, distinguished mainly (well, only…) by the spacing between the relays and input connectors:

• Size S: Input spacing 0.5” (12.7 mm). This is the minimum size I could reasonably make the board. The spacing is smaller than typical RCAs, but would be suitable if you are using different connectors e.g. mini-jacks or if you need to keep the selector board separated and run longer wires to the inputs. This is the same basic size as the ICE-int board.
• Size M: Input spacing 0.75″ (19mm). This is the spacing of many integrated and/or low-cost RCA sockets.
• Size L: Input spacing 0.95″ (24.1 mm). This is the standard size board size which gives a bit more space between connectors and thus allows using better-quality “premium” RCA sockets. It is also the biggest board that can be made to fit inside a 5×10 cm limit as imposed by many board manufacturers.
• Size XL: Input spacing 1.1″ (28mm). This is the standard spacing for Neutrik D-series RCAs/XLRs and so the one that is best suited if you want to stack two selector boards for balanced inputs.

Note: There is no functional difference between these boards. The only reason for using a specific version would be to make the wiring between the board and the connectors as neat as possible.

All boards share the following features:

• Standard “2-form-C” relays are used (Takamisawa RY-xxW series, Omron G5V-2 series or similar). Depending on how the boards are controlled, relay voltages between 3 and 48VDC are possible.
• Universal in/out connectors.
• Power connectors at both ends of the board.
• Stackable for balanced configurations (or if you need more than 4 inputs)
• Space for optional termination resistors on the bottom of the board (1206 SMD footprint), so that unused sources see a finite load instead of an open connection.

How big are the boards?
The board sizes are as follows:

• Size S: 2.6” x 2.0” (app. 66 x 51 mm.)
• Size M: 3.35” x 2.0” (app. 85 x 51 mm.)
• Size L: 3.95” x 2.0” (app. 100 x 51 mm.)
• Size XL: 4.4” x 2.0” (app. 112 x 51 mm.)

What is the status of the boards?
All the boards are labelled v2.5. I originally made a layout much like this back around 2006-2007 which I used as a starting point. Version 2.0 was the first attempt at cleaning up these and introducing more versions. Version 2.5 is because I’ve more recently cleaned up the silkscreen and standardised the control connector pinning to match the switch boards.
These boards were developed separately but should now be completely aligned and integrate without issues. I’ve prototyped v2.0 of all of them except the XL version where I have made the v2.5-version (as shown).

Does it use any special/expensive/hard-to-find parts?
None. The relays can be Takamisawa RY-xxWs or any one of the many similar parts. You should be able to buy these from ebay and any other source.

Anything else I need to know?
Some quick FAQs with answers:

• Q: Can I use the boards to switch outputs instead of inputs?
  A: Yes, however in order to have more than one relay active at a time you will have to do the switching in a different way than what I have done.
• Q: Can I use the boards to switch headphones?
  A: Probably. I haven’t tried it, but I expect it would work. Same caveat as above on multiple outputs though.
• Q: Can I use the boards to switch digital/coax sources?
  A: Well, it’s definitely not designed for that purpose but better dacs might be able to survive the signal degradation. By all means try it, but no guarantees 🙂
• Q: When do I need to use the termination resistors?
  A: Not sure actually. Some sources are reportedly not happy with a no-load condition and in the spirit of versatility I decided to cater for that eventuality as well. If you do fit the resistors they will also serve as a discharge path for any source that has a capacitor-coupled output which might help. Values between 10k and 100k should be fine here.

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.