This is more rambling about the USB charger project. I’m to the point where I’m doing the layout of the circuit boards. In this process I’m in the middle of evaluating a bunch of different pieces of software.

Today’s experiment was Eagle by CadSoft.

It seems to work well enough, but simple things seem to be tripping it up. Like, for instance I want to have a four-wire connection to a resistor — the low-rent version of a Kelvin connection. It’s not 100% perfect, but it’s plenty good enough for the level of precision I’m looking for. (Basically, I’m putting a 10mΩ resistor in series with the 5V line and reading the voltage across it like this from Analog devices)


Should be nice and easy. (Ignore the 1mΩ label, it’s wrong.)

Except it’s not. The different connections have different characteristics. The wire from the OUT pin of the switch through the resistor and continuing to 5V on the USB is a thick trace to handle 2.1A of current. The connection from the the resistor to the amplifier can be tiny since there’s no current there.

Setting things up like that in Eagle seemed to confuse the auto-router.

Meh.

If it worked I might’ve been convinced to throw some money at them.

Tomorrow I’m trying Altium. (I’ve already tried KiCad and that just seems like a hot mess)