First off, I just want to say that I'm still pretty new to PCB and schematics design, and electronics in general, so any suggestions on improvement are much appreciated!

I'm creating a basic circuit to control a string of addressable RGB LEDs. The circuit is powered by a 12v DC wallwart, and then the power is stepped down to 5v to run the heart of the circuit, an ATTiny45. There is also a switch to choose between 5v and 12v for the power output to the RGB string. The micro USB is used for serial communication so I can send commands to a sketch running on the ATTiny to tell it what to display on the RGB string.

As I'm still learning electronics, and as the main parts of the schematic is different schematics I've found from Google searches pieced together, I wanted to get you guys to look over my schematic before I get it printed.

enter image description here

The URLs below some parts of the schematic point to the sources where I found the schematic needed to put together that part.

Any suggestions on improvements, better ways to do things, or critique is appreciated!

EDIT: Changed the barrel jack component to a proper one

  • \$\begingroup\$ 3V6 Zener diode? Doesn't seem high enough to me, despite it being repeated through all the linked documentation. \$\endgroup\$ – CharlieHanson Jan 2 '16 at 22:06
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    \$\begingroup\$ @CharlieHanson USB D+/- signals are 3.3V level. If the MCU is run at 5V, the zeners will drop the voltage level of the signals from the MCU without having any noticeable effect on signals from the host. \$\endgroup\$ – Tom Carpenter Jan 2 '16 at 22:10
  • \$\begingroup\$ The symbol for the power jack looks a bit odd to me - are you sure it is the correct one and that you have wired it correctly? I'm pretty sure that it is drawn at 90 degrees from what you would expect, such that pin 1 is actually the pin of the barrel jack which is usually positive \$\endgroup\$ – Tom Carpenter Jan 2 '16 at 22:12
  • \$\begingroup\$ @TomCarpenter Ha, I appear to have given up using my brain as a New Year's resolution. \$\endgroup\$ – CharlieHanson Jan 2 '16 at 22:16
  • \$\begingroup\$ @TomCarpenter The DC jack is wired correctly for "centre positive" which is the more common of the two possibilities. However, pins 2 and 3 should either be swapped or joined. The two pins are short when there is no jack connected and open when it is. Soldering all three pins to the board is a real boost for phyiscal stability - less chance of pads being torn off the board by an abusive plugger. \$\endgroup\$ – CharlieHanson Jan 2 '16 at 22:23
  1. There should be a low ESR cap on both the input and output of the switching regulator. I didn't look up the datasheet, but didn't it say that? Even if not, it's still a good idea.
  2. You forgot the bypass cap across the microcontroller power and ground.
  • \$\begingroup\$ Aren't there already low ESR caps on the input and output of the regulator in the schematic I posted..? And yes, the datasheet does say it's needed. \$\endgroup\$ – Keith M Jan 2 '16 at 22:51
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    \$\begingroup\$ @Keith: At 100uF each, they are probably electrolytics, so no. Keep them, but add 20 uF or so ceramic caps across them. They will provide much lower impedance at high frequencies. \$\endgroup\$ – Olin Lathrop Jan 3 '16 at 0:06

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