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Archive for February 23rd, 2012

MOSFET rDS PCB

This one came out surprisingly well, apart from the total faceplant with that resistor. With any luck, it’ll measure MOSFET on-state drain resistance over temperature for an upcoming Circuit Cellar column; it’s a honkin’ big Arduino shield, of course.

Drilled holes on the Sherline using the relocated tool height switch:

rDS Tester - drilled PCB

rDS Tester - drilled PCB

Front copper, after etching & silver plating:

rDS Tester - etched front

rDS Tester - etched front

Back copper, ditto:

rDS Tester - etched rear

rDS Tester - etched rear

I think I can epoxy the resistor kinda-sorta in the right spot without having to drill through the PCB into the traces. Maybe nobody will notice?

The traces came out fairly well, although I had to do both the top and bottom toner transfer step twice to get good adhesion. Sometimes it works, sometimes it doesn’t, and I can’t pin down any meaningful differences in the process.

And it really does have four distinct ground planes. The upper right carries 8 A PWM Peltier current, the lower right has 3 A drain current, the rectangle in the middle is the analog op-amp circuitry tied to the Analog common, and surrounding that is the usual Arduino bouncy digital ground stuff. The fact that Analog common merges with digital ground on the Arduino PCB is just the way it is…

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