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Design of PCB Trace Routing

perigalacticon

Looking for advice for designing a PCB with several functions.  I am an amateur PCB designer and only designed one other small board but it worked.

 

This project currently has the following features:

 

1.  5V & 3.3V power regulators.

2.  SPI signals from an ATTINY841-SU SOIC-14 MCU to a Dataflash SPI flash soic-8 IC.

3.  1W audio amplifier to external 8R .5W speaker.

4.  5x WS2812B surface mount Leds.

5.  5X capacitive touch pads (externally connected).

6 2x 6V  2CR1/3N2CR1/3N batteries in parallel

7.  2.25" square PCB, 2-sided, standard options.

 

I am looking for advice as to how to route the traces for best performance, I'm working with Eagle 8.3.2.  This a project for some gifts I am making for Halloween in a quantity of ~50.

 

I am mainly concerned about signal integrity and noise, especially the capacitive touch connections.  Currently I routed these last but there are many vias on these traces and I'm concerned that nearby external objects may affect the capacitance readings.  I could route these first on top with no vias but then the other signal traces are more complicated.  Is SPI sensitive to routing with several vias?  How about WS2812B data signals or small voltage audio signals?  How sensitive should I expect this system to be to routing overall?

  • in reply to perigalacticon

    Is the SPI flash write protect coming from the processor that you're in the process of programming?

     

    Your flash is 3.3V signalling and your micro 5V? Is the flash part 5V tolerant?

     

    Personally, I don't think I would parallel the batteries, but that's just me being squemish about the effect of connecting two batteries with different amounts of charge in them. It's fine after the lower one has discharged the higher one, though.

     

    Peak current on the 5V is possibly something like 500mA (250mA, say, for the LEDs all on and maybe 250mA for 0.5W into 8 ohms). Is your regulator up to that? One way to lighten the load on it might be to run the amplifier directly from the battery voltage, if it will run on the 6V.

     

    Your ground layout on the board leaves a lot to be desired. Some of the paths aren't very direct (a few more vias scattered around would help, particularly next to the ground pins of the chips, the ground reference pin of the 3v3 regulator, and the GND pins of the LEDs).

  • in reply to jc2048

    I'm going ahead with manufacturing, but I realized I need to exclude the touch SMD pads from the tCream layer so they aren't included in the gtp file.  How do I exclude smd pads from the tCream layer?

     

    Thanks.