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CaptainKirk

Member Since: August 31, 2008

Country: United States

  • It’s a peak detector, along with the capacitors and the 100k resistor. The output will generally follow the amplitude envelop of the audio signal.

  • For anyone who’s interested, I made a laser cut acrylic case for mine and uploaded the design to Dropbox. Not waterproof or anything fancy, it just made it easier for me to mount on things (I use it for time-lapse videos mostly).

    It’s a stack-up of 5 layers. In the DXF file, the two mostly solid pieces on the right are the top and bottom, thickness can be whatever you want, I used 2 mm plexiglas. The pieces on the left are 3 mm plexiglas. Cut green first, red second and blue last. It should be fairly self-evident how to assemble, but a couple things are tricky.

    Start with the base, put three 2-56 5/16 inch screws in the holes that will line up with the holes on the HackHD board.

    Place three of the acrylic cut washers over the three HackHD mounting screws. (There’s a spare…)

    On top of the base, place the piece with the full HackHD outlined hole.

    Next position the HackHD camera. I found the holes to be pretty tight. Put nuts on the screws and gently tighten. I had to grind one side of the nut next to the connector to fit.

    Next place the piece with the two hexagonal holes. Place a couple of 3 mm nuts in the holes. (Sorry for mixing metric and English, it’s what I had on hand.)

    Next the similar piece that doesn’t have the hexagonal holes, and finally the top.

    Insert three 5/8 inch 2-56 screws in the other 2 mm diameter holes from the rear and gently tighten with nuts.

    The remaining piece can fit over the screw heads on the back, and with a couple of 3 mm screws of appropriate length the assemble can be mounted on a bracket or what have you. The spacing of these screws is 40 mm.

    https://www.dropbox.com/s/sfadoqzcwrcwtzq/HackHDcase.dxf

  • Tantalums can also explode with high dI/dt, even if the voltage rating is never approached. Battery power can be especially bad for that. Happened on a product I was working on, fortunately we had some prototypes go and redesigned it before it was released. Here’s a paper from AVX with plenty of information… http://www.avxtantalum.com/pdf/SURGTANT.PDF

  • I’ve done this with a different brand of the same stuff. I didn’t get super details like alginate or plaster of paris would give, but it was much easier, and it was definitely recognizable as a face.

    Heat it up, roll it out to about 1/8 inch thick and about 10 inches in diameter, lean back and gently mold it to your face like a big pancake. Let it cool. Cold water helps if you’re up to that.

    You might want to make a small hole over the mouth area, but I found the fit loose enough that wasn’t necessary. And of course in an emergency you can just peel it off and start over.

  • Point well taken. I mostly speaking tonguke in cheek, and thinking back to Polaroid’s PolaPulse batteries. They were 6 volt flat battery packs designed to be built into film packages. Having a large surface area, they could put out a lot of current, and stories circulated that two in series could start a car.
    For these batteries, they should be pretty rugged, but you’re right, don’t try this unless it’s the only way to start your truck while you’re fleeing the zombie hordes.

  • Yes it would. Hmm, two in series might be able to jump-start a car.

  • Without searching through all the other batteries, there are various reasons why the energy density varies. The batteries here can sustain a 30C discharge. Typical Lithium batteries are rated at far lower discharge rates, on the order of 1/2C to 2C. There is a compromise in order to do that safely, and energy density usually takes a hit.

  • The squishy circuits look fun, I’ll have to try this with my nephew.
    I envision extruding rods of this with a Playdough Fun Factory ® and laying out multi-layer boards…

  • (I assume you’re talking about a 5 volt signal driving the gate, referenced to the source.)
    Using i = C * dV/dt, rearrange so dt = C * dV/i, and using the input capacitance, your drive voltage minus the gate threshold voltage and gate leakage current you can get a rough idea.
    But if you notice, the gate leakage current can be either positive or negative. Bottom line: don’t depend on simply removing the gate drive to turn it off.

  • 100 Hertz is trivial for this part, it has a turn on time of 140 nanoseconds and turn off time of 100 nS, but you need to drive the gate properly. While the gate current is negligible, there’s a very large capacitance that needs to charge (look at the gate charge and input and output capacitance in the spec), and when it’s between all the way on and all the way off it will dissipate lots of power, so you usually want to make that transition quickly, though with a 100 Hertz rate that’s probably not going to too bad. Te transient thermal impedance spec will help you there.
    Also, if you’re driving an electromagnet, that’s a big inductor, and when you switch current there will be large voltage spikes which can easily damage the part, so you need to clamp that.
    If you’re new to this aspect of electronics, one great resource is the application notes manufacturers publish, they want to help you use (and buy) their parts. For example, if you go to http://www.fairchildsemi.com/apnotes/power_management.html#MOSFETs and download app note AN9010, there’s a good introduction to how MOSFETs work.
    Hope this helps, and good luck with your project.

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