The Kontraptionist

Member Since: July 1, 2010

Country: United States

  • Eh…. sort of, but the on-resistance will be very high compared to running it off a 5V system. I for one would not consider this a usable option for a 3.3v system. It’ll likely get hot. Look a the datasheet, “Figure 4”

    Those curves on the datasheet are there for a reason - The thermal de-rating stuff really doesn’t (always) pertain to the hobbyist, but gate voltage curves certainly do. Study them.

    You really want to drive the gate with a voltage somewhere around where that curve starts to flatten out. As you can see, at 3V, the chip only begins to conduct. At 3.3V, it’s still not that “turned on” and you can expect trouble if you’re running on a battery and the voltage starts to sag.

    I usually suggest either finding a true 3.3V logic level mosfet (Sparkfun, they do exist, you should probably put one on this board) or using a darlington like the Tip-120, which are far easier to deal with on lower voltages.

    The other option is to use a MOSFET driver, but these are only if you’re using big FETs and want to do things “right” - Face it, some of the bigger, meaner MOSFETS want a 10V gate voltage or more, and you just can’t get that out of an Arduino or whatever. You need a proper drive circuit.

    Just as an aside, and as parts that somebody might just have laying around, the MAX232 chip does a pretty great job of driving MOSFET gates, and it’s got a built in charge pump, so your 5V system can drive mosfets with big gate voltages. After all, it puts out 12V! Don’t expect to get exceptionally high frequency out of them, but for PWMing big fat lights, they’re awesome, and best of all, they drive the gate in to reverse voltage when “off” and that for absolutely sure shuts off the MOSFET. All good things.

  • Adafruit would have put a 26 cent regulator and an I2C level shifter on their version of this board… Just saying. Seriously guys, the purpose of a breakout board isn’t always just to solve the problem of people not being able to solder surface mount. How much does a PCA9306 cost in 250 count? 54 cents. To make the board a ‘whatever you throw at it’ voltage. The value of improvements like these are huge, and now you can plug it in to you Edison OR your Uno. With no extra crap!

  • Yeah a sure heart attack. How many hundred joules are we talking here? By your estimates, assuming a USB port, 5v, 500ma. Or are you assuming that the ground lead of the computer is connected to the hot side of the power outlet? I hear this does happen, though I’m not sure if I’ve heard of it going unnoticed for long. You bring up a good point. Spark fun should look in to this.

  • I’d be a little careful about calling the level shifting circuit “proper” - the resistors in the circuit are 1K - 1K to +5 and +3V3. That’s a pretty low impedance line, especially considering that the Arduino Pro has 1K resistors on the TX and RX lines (why is this by the way???) What bothers me is that the stand-alone level shifter (BOB-08745) has 10K resistors. I substituted 10K (Ask me how fun soldering was with only a regular iron and tweezers) and it at least works now with the Arduino Pro, but it barely pulls “LOW” to 1V

    I should say it works FINE with a Leonardo (and probably the Uno too) because they lack the resistors on RX and TX.

  • Anybody design a 3D printable case for these yet? Also, Sparkfun, suggestion to change the LEDs to side-shining? My two cents!

  • Just wondering if that ATMega328 is rad-hard? :-)

  • The emitter current limiting resistor on the analog versions that are shipping October 2012 are measuring to be 100 ohms. The sensors are actually running pretty warm. The emitters are drawing 34mA at 5V - but a perfect 20mA at 3V3. I know the datasheet has absolute maximum ratings of 50mA, but… I have four of them runing at 5V and they’re all running just over 100ºF. Are we sure this is OK?

  • You’ll never see open firmware. See licensing nightmare rant above. My experience is similar. Imaging technology is so locked down that it’s basically impossible to do anything outside of going to Best Buy and buying a camera. Plan works perfectly.

  • Love it how the Atmel on the shield completely smokes the shoes off the little chip on the Arduino. Why not leave the separate Arduino out of the picture completely? I guess it’s a different compiler? (for the 32 bit?)

  • The MP3 Player Shield has been tested as working with an Arduino Pro 3.3V on both LiPoly and USB programmer power and with an Arduino Uno with no modifications to hardware or code on either, save from the addition of the “9” in !card.init(SPI_FULL_SPEED,9)

    How it will perform on a partially charged battery is another issue that remains to be seen and will depend on the dropout of the voltage regulators, but for now 3.3V performance seems solid and there are no drops in audio at 8 MHz. FYI the Arduino Pro 3.3V doesn’t have 3.3V and 5V pins, just VCC and VCC.

No public wish lists :(