Gas station without pumps

2013 September 3

My son’s first PC board

In Towards automatic measurement of conductivity of saline solution, I complained about not being able to use the KL25Z board, because my son was using it.  What he was doing with was building his first prototype for the light gloves project:

Here is his first PC board design, populated and mounted on the Freedom KL25Z board.  The 5cmx5cm board is a bit smaller than the KL25Z board is wide, so it only plugs in on one side (there is a screw acting as a spacer to keep it from being a cantilever).    He has not yet mounted the Bluetooth module.

Here is his first PC board design, populated and mounted on the Freedom KL25Z board. The 5cm×5cm board (the cheap size from Iteadstudio) is a bit smaller than the KL25Z board is wide, so it only plugs in on one side (there is a screw acting as a spacer to keep it from being a cantilever). He has not yet mounted the Bluetooth module.

The prototype board has many differences from the final design: no battery, no battery charger, no buck/boost regulator, no flash memory, no processor, screw terminals instead of jacks—even the LED driver chip is different, since the chip he plans to use is only available as a surface-mount device. But there is enough of the design here to start demoing and writing code.  They are hoping to keep the final board below 5cm×5cm, so as to get low PC board prices even in very small production runs.  That will mean all surface-mount parts, so I think I’ll have to get a hot-air rework tool so that they can assemble a prototype—I’ve been thinking that I might want one for myself to play with surface mount designs, so this isn’t really a hardship.

My son still owes me some money for buying him the PC board run, the screw terminals, the Bluetooth module and some heat-shrink tubing. It is a bit annoying that he isn’t old enough to get his own Visa card, so that he can do his shopping without me as an intermediary. (We’re not talking big bucks here—we’ve spent more on pizza for him when they work through dinner than they’ve spent on all parts combined.)

I’m pleased that he got his first PC board working on the first attempt—he did the design entirely on his own, though he did ask my advice about things like via sizes and how fat to make the wires. Since there can be moderately high currents for the LED driver, I recommended that he make the ground and power lines as fat as he could, and he decided to do a flood for each. The board looks quite nice:

The top view of the board with the screw terminal to be mounted on the top and sides, the header on the lower left, and the Bluetooth module on lower right.  The hole near the top right is for the screw that acts as a spacer.

The top view of the board with the screw terminal to be mounted on the top and sides, the header on the lower left, and the Bluetooth module on lower right. The hole near the top right is for the screw that acts as a spacer.

stationary-glove

This is what the glove looks like with the five RGB LEDs lit up (I understand that the final design will have more LEDs—but the through-hole driver chip has limited pinout). They don’t have the user interface written yet, so the lights were set up by a quick-and-dirty Python script talking to the KL25Z board over a USB cable (which is also supplying power).

waterfall-glove

They have not implemented programmable flashing yet, but the pulse-width modulation (PWM) frequency is set very low here (much lower than what they intend to use in the final design), so that one gets a stroboscopic effect even with steady light settings, just from the PWM. That’s not my son in the picture, but the high-school student who started the project—my son has done most of the electronics and programming, but did not originate the idea.

The two teens spent a big chunk of the day wiring up the LEDs and writing a small test program, as they want to demo the glove tomorrow for the back-to-school event. It may also be an enticement for teens to join an Arduino/microcontroller club—look at the cool stuff you can learn to make!

arc-glove

Another view of the prototype light glove in action.

Once they got the demo working, they invited over a third member of the team to do some brainstorming about what else needs to be done (and how they’ll do it). It looks like they’ll be talking half the night.

Since it is clear that my son will be spending a lot of time on this engineering project this year, we decided to make it part of his official school work.  In addition to the engineering design work, he’ll also do some a paper for his econ course (on pricing the components and manufacturing, and setting a retail price for the gloves), and papers for a tech writing course.

His first tech writing assignment is to write up a description of the color space he decided to use for representation of colors in the program, and why he chose that color space out of the dozens available.  He spent a week thinking about color spaces anyway, before settling on a commonly chosen one—so writing up that reasoning for the other members of his team will be a good writing exercise.

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6 Comments »

  1. See if he can get a Visa or MasterCard debit card on his bank account. My daughter’s ATM card for her account is a Visa card, so she’s been able to use it for online purchases….

    Comment by Jo in OKC — 2013 September 4 @ 09:09 | Reply

  2. Cool! My daughter has a Paypal account and debit card that she uses for shopping online and in stores. I wasn’t the one who set it up, so I’m not sure on the details, but she’s had it since she was 14 or so. I think her account is linked with my husband’s. She also has a debit card for her credit union account but tends to save that one for emergencies.

    Comment by kcab — 2013 September 4 @ 16:50 | Reply

    • I just checked with our credit union (where my son has an account already). By our co-signing, he could have had a debit card as young as 13 years old. I’ll be getting him his own card as soon as we get back from our college tours this week and next.

      Comment by gasstationwithoutpumps — 2013 September 4 @ 17:15 | Reply

  3. Reblogged this on Archival Detritus and commented:
    What you can do with your time if you are teenager and do not have to go to school….

    Comment by tashadepp — 2013 September 13 @ 10:07 | Reply

    • I don’t think that all teenagers are capable of or interested in PC board design. Homeschooling has allowed my son to explore his interests more deeply than if he had all the busywork of traditional high school, but I’ve met several home schoolers who just use it as a way to do less, not more, learning.

      Comment by gasstationwithoutpumps — 2013 September 14 @ 11:27 | Reply

  4. […] set of prototype boards for the Infinity Gloves.  (I blogged about the first set last September in My son’s first PC Board). This second set was all surface-mount components, so they had the prototype boards professionally […]

    Pingback by Infinity Gloves prototype board | Gas station without pumps — 2014 May 2 @ 18:51 | Reply


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