Member Since: April 7, 2012

Country: United States


I’ve been developing hardware and software since my youth - an early project was a matrix display (5x7) using flashlight-style incandescent bulbs wired via homemade 36 wire cable to an array of screw heads on which a metal template could be placed to light up corresponding bulbs. Since then I’ve designed weather stations, test equipment for aircraft electronics, energy management systems, and all sorts of other things. I’m currently doing some Arduino and Raspberry Pi based projects. I was the technical reviewer (editor) for Beginning C for Arduino, published by Apress, and am working on some additional books. You can find more at

  • I use DesignSpark PCB for layout. It isn’t open source, but it is free to use (including for commercial designs). It can produce gerber files, and has an autorouter. It can handle multi-layer boards, up to 1 meter x 1 meter in size. It doesn’t have some high-end features like buried vias or automatic differential pair routing, but I’ve found it more than adequate for typical boards. I’ve found it pretty easy to use. It is provided by a large worldwide electronics distributor (RS Components (unrelated to Radio Shack), which also owns/operates Allied Electronics here in the US), You can find it at RS Component’s DesignSpark Community website. They also offer a free mechanical CAD program.

  • I’d also like to know: Are the AC measurements RMS? and Is the USB electrically isolated? If not, you could run into problems quickly measuring circuits connected to an AC line.


  • I’m curious - a quick search shows the APDS-9960 chip for sale thru Asia-Pacific and UK region distributors, but not US distributors. Anybody know the reason behind that? Patent issues?

  • On the Connecting the Hardware page of the tutorial for this, it says: “The four pins you need are labeled GND, 3.3v, OUTPUT, LO-, and LO+”

    Um…, that be five pins, folks. :-)

  • I still have some calculators that use these. They also remind me of this passage from Isaac Asimov’s book, Foundation, written in the early 1950’s, long before these were available:

    Seldon removed his calculator pad from the pouch at his belt. Men said he kept one beneath his pillow for use in moments of wakefulness. Its gray, glossy finish was slightly worn by use. Seldon’s nimble fingers, spotted now with age, played along the hard plastic that rimmed it. Red symbols glowed out from the gray…

    By the way, some of the 4-digit displays of similar digit height that are current and available (made by Avago (spin-off from HP), Osram, and others) are, as others mention, much more expensive. But they are also full alphanumeric, with a 5x7 dot character, and have intelligence built in for driving them. So some aren’t that much more expensive than these bubble displays would be with a backpack controller board.

  • More from the data sheet:

    The accuracy is -2/+0 hPa typical, -6/+4.5 hPa over -20C .. +65C temperature range.

    The resolution is gets down to 0.02 hPa. But resolution is not the same as accuracy.

  • And another Schematic/PCB editor to consider is DesignSpark PCB. It isn’t open source, but it is free, without limits on board size or commercial use.

    I’ve also used a higher-end commercial package at a past employer, and free ExpressPCB in the past for prototypes.

    ExpressPCB is easy to use, but while it is free, it doesn’t output gerbers, so you are limited in who you could use for the fabrication unless you “buy” gerbers for your design from ExpressPCB. It is also more limited in other respects.

    I’ve found DesignSpark PCB to be roughly comparable to the commercial package I had used. It has its share of annoyances, but some really nice features, too. The biggest hindrance for a beginner is the schematic library symbols for many common parts tend to be rectangles, with properly numbered pins, but not the more common functional symbols like triangle for op amp, etc. You can add your own symbols to the library, though, and easily associate them with the components. (I plan to share a library of such symbols I’ve created, in order to make it easier for (I think) the majority of us who prefer the functional symbols.) The other downside is that its only native version is for Windows. The other up-side, though, is that it has footprints for a very large library of parts, and in many cases has multiple footprints available for the same package, following IPC standards for dense, normal, and loose (hand-solder) designs.

  • Static data is initialized to zero in the C and C++ standards, before any explicit initializers are applied. It would certainly not hurt to include ‘\0’ at the end of the card initializer constants, though. Also, it looks like there is an extraneous extra single quote before the first initializer in the code listing.

  • One case I can thing of for a copper pour other than power or ground is for heat sinking. On some power devices the tab is not electrically isolated within the package, and may not be fixed at ground potential in your circuit. But you may want a large area of copper tied to it to help convey away the heat.

    The other cases I can think of are where you might be using the a copper pad as part of an intentional capacitor, for capacitive touch sensing.

  • Thanks for mentioning the SN74LV8153. I’m familiar with many chips for driving LEDs, but hadn’t noticed that one. Nice that it supports output up to 12 V, handy for some of these larger digits that have two LEDs in series for the segments. And not pricey like the Maxim parts.

No public wish lists :(