• Stress Testing 04

    Friday, April 4, 2014

    4/4/2014— Eric Kolker

    Hey Tessellators, Eric here.

    The pressure to ship is enormous. Every day that we take to verify or double check something related to the hardware means another day that you have to wait for your Tessels.

    On the last version, the power plant wasn’t perfect.

    Bye, bye black boxes

    In my post last month, version three introduced a new voltage regulator and related support circuitry, including a new power multiplexer IC. When we fired up the boards, it became clear very quickly that the specific power mux part was, quite literally, throwing an error and shutting down during certain normal-operation conditions.

    At the time of my last post, we knew of another part in the same family that would theoretically allow us to sidestep the issue. Mr. Murphy and his law had other plans, however, so we did what we always do: overnighted parts for a new design, stripped down the latest board, and patched in the new design. Here’s what the patched-in version looks like (disconnected from the Tessel):

    The new design is as simple as possible and to eliminates the more specialized ICs I had been using before. I wanted to know exactly what was inside of the chips I was using, not rely on someone else’s fancy (and unpredictable) design. The result has a larger solution size (EE jargon for “it takes up more space on the board”), but is much more transparent. Fortunately, it also works like a charm. Our power input stage now looks like this:

    Stress tests

    Just as software must pass its unit tests, hardware has its own suite of tests that need to be run to make sure it’s ready for prime time. These include a traditional burn-in, as well as lots of different scenarios related to how the device is powered.

    Part of the initial power plant redesign gave Tessel the ability to run off of more than just USB power, giving you the freedom to use virtually any battery under the sun to power your Tessellations. However, with great power comes great responsibility, so I knew I had to be sure that, no matter what you do to Tessel, it won’t give up on you. This means that I spent all of Thursday abusing the input power path. It’s been terrifying but, honestly, a lot of fun. Here’s where we are right now:

    • Tessel can be powered off up to 15 V on the VIN pins by the USB port (~3.4 V is probably the lowest you’d want to go)
    • It can also withstand power being applied backwards to the same VIN pins and live to tessel push myCode.js another day
    • Tessel switches automatically between USB and external power (depending on what’s available and with a preference for USB) without rebooting or halting code in any way.
    • The voltage in to the DCDC converter tracks the input voltage beautifully (read: within ~0.3 V and better with for higher input voltages). This voltage is broken out at the GPIO bank, but should not be used as a source of significant current.
    • If you accidentally short the pins which provide power to the DCDC converter (the voltage regulator that takes in up to 15 V and gives us 3.3 V out), Tessel does not care, and will turn on again once the short is removed.

    As an aside, even though that’s a pretty good list, I’m going to ask that you please read the docs if you plan to power Tessel through the VIN pins, never power Tessel through the GPIO bank, and try to avoid shorting anything. At the end of the day, I can do my best to protect the Tessel from abuse, but there are a lot more of you than there are of us.

    Running the tests

    Testing hardware is, frankly, a lot more exciting than testing software. With software, the worst that’s likely to happen is a BSOD or a string of error messages, after which you track down bugs and try again as quickly as a minute later. With hardware, there’s a very real chance that something burns, melts, catches fire, or generally releases its magic smoke.

    Sometimes, the testing is deliberately destructive. This poor -03 was my guinea pig for many of the power plant hacks.

    Other times, the goal is to test things over and over again, like the self-input-switching Tessel Jon rigged up. Sometimes, though, repetition and boundary-pushing are combined, like in this video, where I repeatedly short out Tessel’s input power and the board keeps chugging along.

    What this means for you, patient reader

    Pending any fires at TMHQ (Greentown Labs), Jia is in the process of talking to our manufacturers about making 2500 of these boards (pre-sales are a little below 1500 right now, but we wouldn’t want to run out a month or two after launching, would we?). As we said in a recent post and backer email, we’d have about a month between signing off on the run and the first batch of boards hitting our desks.

    At this point, we’re ready if you are.


    #update #eric kolker #stress #testing #stress testing #power #tessel #technical machine #tessel 4 #test

  • Friday, April 4, 2014

    #update #eric kolker #testing #voltage #power #tessel #technical machine #electrical engineering #test

  • Final Hardware Testing

    Thursday, April 3, 2014

    4/3/2014— Jon McKay

    Tessel version nine arrived at our office yesterday. It came in yesterday straight out of Worthington Assembly’s ovens.

    Each new hardware revision means a whole slew of tests to make sure we fixed any known problems and haven’t created any new ones.

    Eric is testing out how robust the board is after merciless shortings on both USB input and external power lines. He had designed new power circuitry to try and prevent the board from being fried in the event of a short and preliminary results are looking promising.

    I have a test rig to put our power switching circuitry through the hoops. Tessel can be powered off of USB or external power (up to 15V). We want users to be able to program Tessel over USB, then detatch out the USB cable and have their program continue running off of external power (if it’s connected) without a hiccup.

    Yes, the header on the old relay modules were assembled backwards and yes we are embarrassed. This relay module is plugged in upside down, and if you do that with the production models they won’t work.

    My test rig (above) has both USB and an external LiPo battery connected to Tessel at the same time. The USB power is intercepted by a debugging circuit board (below) that allows us to splice off USB power into a relay connected to Tessel.

    That allows Tessel to tell the relay to either connect the USB circuit or disconnect it. That is, Tessel is testing its own power regulation circuitry by switching its input power between USB and the LiPo. If the switch fails, Tessel will stop blinking lights because the program is stored in RAM and will be erased on power failure. Tessel testing itself is a beautiful thing.

    It both terrifies me and excites me that this revision of the board seems to be working to spec (knock on wood). If all goes well, we can be set to start up production early next week.

    Jon McKay

    #Update #Jon McKay #Electrical Engineering #Tessel #Technical Machine #Revision #Hardware #Testing #Test #Power #USB

  • Update: Shipping Schedule

    Tuesday, March 25, 2014

    3/25/2014— Updates

    Where we’re at on the reset issue:

    We got the pre-production boards back and have confirmed that the reset issue is fixed. But one of the parts used in the updated power plant did not perform to spec when placed on the Tessel (off-board tests worked fine, even when wired directly into the Tessel). The issue is only apparent when Tessel is powered over external power (not USB), but we don’t feel comfortable shipping something that is not working perfectly.

    We did another redesign of the power plant to fix the issue, and have sent out Tessel to the manufacturers for another test batch.

    What this means for scheduling:

    • Test batch: We’ve pushed out a new design to fix the power plant. We expect to get it back in about 1 to 1.5 weeks.
    • Manufacturing: Once we’ve determined that the new design works, we tell our manufacturers to go ahead. They start making them and then send us the batch in about a month.
    • Fulfillment: We send everything over to our fulfillment house, and they start packing up and sending off orders right away.
    • Shipping: Our fulfillment house will send you tracking numbers when they put your package in the mail. After that, domestic orders (USA) should receive Tessels in 2-7 business days; international orders should arrive within 2-3 weeks.

    Then you’ll have your Tessel!

    We’re working on making an excellent installation/first run experience, and we are currently setting up a forum, in addition to improving and finalizing firmware.

    Other news:

    We’ve added a link to the top of the status page that will take you to the latest updates-related post on our blog, so you can check there to make sure your information is current.

    Back to work!
    Kelsey, Jia, Jon, Eric, Kevin, and Tim

    #update #updates #tessel #technical machine #manufacturing #electrical engineering #reset #power

  • Tuesday, March 25, 2014

    #hardware #jia huang #tessel #technical machine #manufacturing #presentation

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