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c-scott

Member Since: January 28, 2010

Country: United States

Profile

Organizations

One Laptop per Child Foundation (OLPC), Wikimedia Foundation (WMF), litl LLC

Programming Languages

yes

Universities

Princeton, MIT

Websites

http://cscott.net

  • On the theory that at least some of the people visiting this page are looking for a diode with as little forward voltage drop as possible (for example, in a battery-powered project): there exist ICs which implement an “ideal diode” (that is, with extremely low voltage drop). For example: the LTC 4412 from Linear Technology, which has a nice digital output to tell you if its on battery power or not. It would be really nice if SparkFun would stock a breakout board for the LTC4412 or one of the other ideal diode ICs.

  • No datasheet with dimensions?

  • I’d double-check your wiring. Grounding the gate should turn off the LED strip. Raising the voltage above 2.5V should turn the LED strip on. Don’t let the gate go above 20V.

    The fact that the led strip is doing something in response to gate voltage changes would seem to indicate wiring error rather than a busted device. Usually letting the smoke out leads to solid-on or solid-off behavior in my experience.

  • Yes: use a pull-up/pull-down resistor to ensure that the gate is discharged. You should never let the gate of a FET-style device float. That stray capacitance picks up all sorts of things from the environment (RF, stray electric fields) and unpredictable things will happen in a circuit with a floating gate — including destruction of the device in the worse case (stray electric fields can cause latch up, although this is not common).

  • Sounds like the right hook-up to me. Double check your “pin 1” etc against the datasheet. I find it easy to mix up the sides of this device. It’s also possible there’s static damage; MOSFETs are traditionally very sensitive to static. Modern devices aren’t nearly as sensitive as in the “old days”, though, and I’ve routinely handled MOSFETs with no special precautions without doing any damange. (And static damage tends to show up as a degradation of, eg, current-handling capacity, rather than a complete “shorted on” failure.)

  • The label on the schematic for the connector is misleading. MIDI is a differential signal on a unidirectional cable. There’s no “in” and “out”, there’s just “plus” and “minus” of the differential current signal. Compare to http://www.midi.org/techspecs/electrispec.php . It looks right to me.

  • Hm, looks right to me. Maybe your Arduino is slightly off? (Then again, I’m using Sparkfun’s arduino breakout footprints on all my stuff, so it’s not surprising that it matches this board. But I find it hard to believe that all of Sparkfun’s products have the wrong spacing here…)

  • Did they say “pay”? They said “license”. That’s different…

  • So… if we’ve got a product we’re working on that we’d be interested in working w/ SparkFun on — do you prefer we send one 10-page email to Spark@SparkFun.com covering points 1-5 of “the pitch”, or make a more informal (say) 1-paragraph introduction first? Or hop on IRC and chat with folks there…

  • The other rule of thumb is that diodes are often placed to “clamp” or “limit” current. If you see a diode going from an input to ground and other input to +v, those are there to limit voltages to within the diode’s forward voltage drop of Vcc/Gnd. The designer doesn’t really want current to flow in those diodes, but they prevent worse things from happening.

    The final common use of diodes is back EMF protection around inductive loads – usually relays or motors in hobbyist circuits. These are a special case of the clamp diodes listed above, although explaining why they are necessary is nontrivial.