I’m working on a board which has a arduino pro mini piggybacked onto it (it’s for semi-permanent installation in a prop). The system is powered by a 12v SLA battery (I need the 12v because of a separate audio amp).
I found out the hard way that Eagle’s 8mil default traces aren’t going to cut it for the 12v input to the board (the traces burned right off the board ). I’m going to spin the board, with a wider trace (32 mils – is that enough?) on the power and ground inputs (connected to “GND” and “RAW” on the Pro-Mini).
However, looking at the Pro-Mini PCB, those tracks are 8mil also – am I going to just burn up the tracks on the Pro-Mini instead? Should I just hang a 7805 on the board and not rely on the Pro-Mini’s vreg?
it’s possible that there was a short, but I don’t think so … I’ve been running the board with the Arduino’s programming connector (no, they weren’t both connected at the same time), and I’ve never had the host system complain about high-current draw. This was the first time that I ran the system free from it’s umbillicus. The board just reads some switches and MUXes a bunch of LEDs (max of 7 at a time @ 20ma – so 140ma + arduino?
I haven’t repaired the trace yet, because I’m a little leery of smoking the Arduino … I guess that’s a risk I’m going to have to take
I’d Ohm out that load side of that burned trace before replace it just to be sure there isn’t a short.
Another trick is first use a resistor (50-1000 Ohm) to limit current in case there is something shorted or drawing too much current. Monitor the voltage drop across the resistor to know how much current is being drawn. Is it reasonable?
Do use a resistor with a large enough power rating so it doesn’t burn your finger if there is a short (don’t ask how I learned that).
If you’re burning out an 8 mil trace; you’re doing something wrong. Likely; you’re exceeding the max input voltage of the onboard voltage regulator. The arduino guys don’t spec exactly which part is on there as the voltage regulator, but they do say 12V max as input.
12V SLA’s commonly float at 13V+. All in all, add a 7805.
). I’m going to spin the board, with a wider trace (32 mils – is that enough?) on the power and ground inputs (connected to “GND” and “RAW” on the Pro-Mini).