First Board Prototype

Archive BatchPCB
1

Hello everyone,

This is my first time creating a board, and I am not sure if I did everything right.

If you guys wouldnt mind, I would appreciate it if someone would look over it and see if there are any obvious mistakes. Like I said, I have never done this before and I know nothing about different parameters of a pcb, so I just want to make one sure I’m not making any stupid mistakes.

The basic premise of the board is to take a signal from a RS232 GPS and display the output on the LCD. It also takes in an analog signal to display on the screen, as well as some other digital outputs for led’s and buzzers. Everything is based around the ATMEGA644p.

Thanks,

Greg

2

Schematic:

  • Aref on processor should connect to a 100nf cap to ground

  • I would add another 100nf bypass cap on the processor and one on the LCD. Rule of thumb is one bypass cap per power pin on an IC

  • I would redraw the schematic to eliminate the 4-way connection at L1/C4 - 2 three-way connections make it clearer, since then all 4-way intersections are non-connected

  • It’s not clear if you intend this circuit to be powered from USB; if so, add a note that the “+5V” connector in the upper right is an output. If not, then you have two sources of Vcc tied together (the +5V connector and the USB connector)

  • Add a ground to the spare_dig_io and RX/TX_header connectors.

  • You are missing a connection dot between ground and the Contrast_pot and gain_pot connectors

  • The MAX3232 wants 100nF ceramic capacitors, not lytics

PCB

  • I would grow the ground traces to reduce their inductance

  • You have some silkscreen/via collisions

  • The processor’s bypass caps should be right next to their power/gnd pins

  • The crystal should be closer to the processor, and the crystal’s capacitors should have their grounds go directly to the processor (though I have been known to tie them directly to a ground plane…)

  • Traces should connect at right angles; otherwise, you can create acid traps

  • Some board houses don’t like silkscreen on pads.

/mike

3

Mike thank you very much for your recommendations. I will be making some changes.

4

n1ist:

  • Traces should connect at right angles; otherwise, you can create acid traps

Do you mean “should” or “shouldn’t”? I thought the usual advice was to avoid 90 degree connections?

–Philip;

5

If they must, traces should connect at right angles (T junctions); connecting at an acute angle is what makes the worst acid trap. Traces should not have right angle (L) bends, to avoid acid traps and underetching.

There are issues for avoiding both T junctions and L bends, including reflections (for higher frequency), stubs, and corona (for high voltages).

/mike

6

n1ist:
If they must, traces should connect at right angles (T junctions); connecting at an acute angle is what makes the worst acid trap. Traces should not have right angle (L) bends, to avoid acid traps and underetching.

Ah, right, thanks for clarifying that–I misread your original statement. :slight_smile:

–Philip;