Member #394180

Member Since: December 31, 2012

Country: United States

  • Thank you for the suggestion, but if I don’t normally buy it it’s because I’ve read the data sheets and tutorials and watched the videos and decided that I don’t need/want it. My workshop (makerspace for the newbies) is filled with stuff from the 19th century up to last week (wanna see an Edison used as an iambic Morse code keyer for a 1-tube radio transmitter in a 3D-printed box?) so being stuck in a technological rut is not a major problem for me. Just saying that the current incarnation of Free Day has the potential for major frustrations, disappointment and can be a money waster because it’ll cost a lot more than the putative penny and that it makes more sense to just order what I want instead of living in bogus hope. If you enjoy it, I wish you the best of luck and I’ll be out of your way on Free Day.

    Love the snail/turtle metaphor, BTW.

  • So I line up $75+ worth of purchase to avoid shipping, race the herd through the gate, may not get anything at all, or if I do it may be something I don’t want, for a best possible case of savings of $39.94 (if I limit the calculation to things I actually want, best case is $19.94) before tax. If I don’t get what I want I’m pissed off at Sparkfun for another lame promotion. If I do get what I want, I’ve spent north of $75 to save less than $20. Logic says to just order the thing I want, eat paying full price and use the cheapest possible shipping. I’ll still come out many 10’s of dollars ahead.

    The old silent surprise Free Day was much better. It was a gratuitous treat handed out to customers who were ordering something they wanted anyway, a thank-you. This just adds in the worst and most frustrating aspect of the Dumpster Dive turning it into a cynical attempt to whip up a feeding frenzy and prey on people who’ve slept through math class.

  • +1 for 1.75 mm. Currently, I get mine from Adafruit but it’d be nice to have an alternate supplier when they go out of stock.

    I’d also like to see a filament sample pack, something like 2 meters of filament so that I could try out interesting ones to see if they work in my printer. A pack light enough to ship by USPS First Class would let me get it quickly and without postage overwhelming the economy of a cheap tryout.

  • Ooh! New question for the Mensa test!

    Given a website with a search function, determine its category for 3-D Printing.


    Lathe, screwdriver, 3-D printer, Donald Trump. Which does not belong in the “tool” category?


  • Why does everyone always contrast gun ownership with gayness? Aren’t there any LGBTQ gun owners out there?

  • Fume hoods are appropriate. Think of all the nasty carcinogenic solvents and cleaners used in electronic assembly that you don’t want to be inhaling.

    I’m more concerned with the utter lack of ESD equipment - no ESD mat, anti-static labcoat, grounding strap, she’s wearing makeup and a ring, and so on.

    Also doesn’t help that there’s a battery still in place on the circuit board and that nothing is keeping the board from sliding around the table.

    The lack of ear protection is also going to be a problem once that soldering iron heats up. Even if her scream doesn’t pop an eardrum, the profanity will.

    These pictures would probably make a great hiring interview item for board fab techs - what’s wrong with this picture?

  • Are you OK with a tutorial showing how to connect 2 devices that both have only USB A connectors?

  • This seems like a solution looking for a problem. It does look like a fun toy, but what’s the point?

    I just bought a brand x (starts with D, ends with ell) laptop that is lighter, has more RAM, has a more capable CPU and has 32GB of solid state hard drive for over $110 less. It’s also got wi-fi and Bluetooth and does not run off of a corruptible camera memory card.

    Throw on your favorite version of Ubuntu to get the full Linux experience. If you want to do Pi-like GPIO programming, buy a Pi, SSH or VNC in and you’re still $75 ahead.

  • Another possibility is to use jerk instead of acceleration. When the bag is punched, the momentum imparted by the fist generates an acceleration. Assuming that the rate of change of acceleration (jerk) is greater from a fist impact than from all the other sources of acceleration changes, it’s a simple matter to take the instantaneous derivative of the acceleration magnitude to get jerk and then apply a threshold. Anything greater than the threshold is a hit.

    Using this approach with a very quick and dirty threshold calculation, the 77 hit data set comes up with 82 hits.

    To calculate the instantaneous derivative, no calculus is needed. Simply remember that the derivative of a function is the limit of delta x / delta y as delta y goes to 0. Since our data is coming in at a more or less regular interval, we can approximate this by subtracting the current magnitude of the acceleration vector from the previous value and dividing the result by the time difference between the 2.

    You’ll end up with positive and negative values. One is the result of fist impacts, the other of the bag hitting its stops and bouncing back. I made the assumption that the fist impacts are going to be harder, so I took the side with the largest jerk, which in this case was the positive side.

    Again, I eyeballed the threshold from a plot, but you could do something more sophisticated like a statistical analysis of the jerk values and set the threshold at a certain number of standard deviations. Enjoy

  • OK, so that was gravitational acceleration. I had made it out to be about 500 just from visually examining my plot of the magnitudes. Of course, since I was looking at magnitudes and x & y never go to 0 (probably due to noise and thermal effects, as well as the bag not being level) 500 is a perfectly reasonable value when the vector math is done to find the magnitude of the acceleration vector.

    BTW, Nate, you could have also used a microphone near the bag, done an FFT of the incoming audio and looked for the components that indicated a hit. That way you wouldn’t have to have modified the bag.

No public wish lists :(