PCB Layout standards for synth modules

[magman]

I'm planning to get into designing some PCB's for circuits in the near future and wondered if there were any preferred standards that can be adopted to make these PCB's more useful to the community.

I've had a scan of the forums and I've seen a few idea's that could be of use, but I thought it might be worth asking the question to see if there are any obvious ones I've missed. Also, it may be useful to have these design standards in one place.

So here goes.

Power Supply - a choice here between the .15" (4 or 6way) connectors used by MOTM and others or the .1" pitch 16 way used by Doepfer et al. Is it worth designing both sets of pads on a board if you have the space, or can adaptor cables be made. My personal preference is for the MOTM style, but I've got no investment in either camp at present.

Pot & Switch connections - these should be grouped on the periphery of the board and have pads and holes capable of accommodating .1" pitch connectors. Also, PCB mounting of Pots and switches should be avoided if the module is likely to be used in different module sizes (FRAC, Modcan, etc), unless on an optional additional board.

IC's - Space should be left around IC's so that sockets can be used if preferred (in other words, don't squeeze components too close to IC's unless space is at a premium).

Resistors - should be spaced to accept a minimum of 1/4W Carbon Film, unless a larger power handling capacity is required.

Capacitors - Electrolytic capacitors should be Axial rather than radial, unless vertical space is at a premium (a particularly slim design is required to stack boards for example).

That's all I can think of for now, with perhaps the PSU and Pots questions being the most critical.

Any thoughts of issues that I may have missed? I'd also appreciate comments on your preferences for things like the PSU connections.

Regards

Magman

[Luka]

after building a xoxbox i realised how much you can pack resistors into pcbs
no point having them all flat on the pcb, may as well have the half standing.
it makes it pretty easy to use aligator clips to test different points of the circuit too

[Tim Servo]

Looks like a reasonable set of rules, except for the restriction on radial capacitors. I generally use radial caps in my designs (especially for larger values) as they take up a lot less PCB space. Unless you've got a huge cap, having them stand up in an axial configuration should still allow you to stack boards with a reasonable amount of space between them.

Don't forget that the MOTM style DC input connector is actually on a .156" spacing, not .15"

I like putting the connections for panel components around the periphery of the board, and (generally) agree with not using PCB mount jacks and pots. It can be very convenient to do a board with panel mount pots and such, but it also limits you to specific components in a specific layout. This might be more acceptable for standalone products, but you might want to rethink this for a module PCB.

I've also attached a pic that shows how I do the connector wiring and pin assignments. Note that Pin 1 gets a square pad on the PCB, and that the polarizing tabs on the PCB connectors (if you use them) should be oriented towards the inside of the board, rather than against the outer edge. These aren't hard and fast rules, especially the pin assignments, but it's just a setup that I find works well. This is, for the most part, copied from the Synthesizers.com specs (although I think I do my pots backwards from theirs). I think the most important thing is to document how your board is supposed to be set up, and then be consistent for your other boards.

Tim (consistent... most of the time) Servo

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Connector Wiring.jpg
Description:	How I do my connector pin orientation and pin assignments
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