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Comment: Re:My comments (Score 1) 107

by Ronin441 (#49718145) Attached to: Turning an Arduino Project Into a Prototype

TXD/RXD aren't used as part of the 6-pin header: it's +, -, MISO, MOSI, SCK, RESET.

Once you've burned the bootloader using the 6-pin header, of course, you can switch to using USB or serial to program from the Arduino environment. And yes, if you're using serial to send down a new version of the code once every five minutes during development and you're also using that same serial port in your application, then moving jumpers around to redirect the serial could get old fast. I'm thinking you only need to do this on RXD -- if TXD goes out from your board to several places, I don't see that causing any problems.

Capacitor polarity: if I fear I've mounted one wrong, I flip the board: pin 1 (i.e. positive) is a square pad.

Mounting holes: good point!

Incidentally, the correct number of mounting points is three, because three points define a plane. If your enclosure flexes, and you have more than three screws holding your board down, then your board has to flex with it. If you have exactly three, then the board remains flat (though not necessarily level) when the enclosure flexes.

I agree with what you say about optoisolators. I'm using a 4N35, but you must bias the base of the optotransistor by tying it to ground with a 10kOhm resistor or so: without this the slew rate (and therefore the bit rate) is appalling.

Comment: Re:My comments (Score 1) 107

by Ronin441 (#49715821) Attached to: Turning an Arduino Project Into a Prototype

ExpressPCB comes with a schematic tool nowadays: ExpressSCH.

I agree that doing a schematic first is definitely a smart thing: the pin assignments on the CPU don't make any sort of sense that was evident to me, and the mapping between Arduino pins and CPU pins is similarly nonsensical. Doing a schematic gives you a much better chance of getting it all straight on your first try. (That's certainly the way I've done it.)

Comment: My comments (Score 3, Informative) 107

by Ronin441 (#49710313) Attached to: Turning an Arduino Project Into a Prototype

If your time is expensive and you will only be running a very small number of PCBs, consider using ExpressPCB's design tool, because it's easy to learn and it seamlessly connects to their board printing service. (Their service is expensive though, so this is only good if you're doing a few boards, and thus the labor you save will not be eaten up by the extra you pay per board.)

Your perception of size on screen is very different to real life. Print a paper dummy of your board. Try to avoid components with pins any denser than SOIC or 0805.

Consider putting a bridge rectifier just after your DC IN connector. Then the polarity of incoming power doesn't matter: the bridge rectifier sorts it out. (It costs you a small voltage drop, of course.) Or use a connector that's hard to get backwards, such as USB or USB micro.

Tie the RESET pin to Vcc via a resistor. A floating RESET pin may lead to random resets. (I made a PIC board that reset when you brought your hand near it.)

Make sure you put the crystal close to the CPU, and connect to it via short traces. Same with the two capacitors either side of the crystal.

Your first draft will contain errors. Expect to have to trouble-shoot these.

Tie any unused digital lines to places where you can populate LEDs for troubleshooting and diagnostic info.

You'll need to include the six-pin programmer header: your CPUs will arrive blank, without the Arduino bootloader.

When you receive your first blank board, first populate the bare minimum components needed to make the CPU run. Then connect to it from the Arduino software on your PC and burn the bootloader into it. (You'll need a programme.r) (If you've never burned a bootloader, re-burn the boot loader on your actual Arduino to make sure you have all the steps and setup correct.) Only once your CPU is running should you populate further components. This particularly applies if you're using the MOSI, MISO or SCK pins: once you connect these to other chips on your board (e.g. you're using them for SPI), you may be unable to burn the bootloader.

Comment: Re:Uh... anyone check electric grid capacity? (Score 2) 327

by Ronin441 (#45249871) Attached to: 8 US States Pushing For 3.3 Million Electric Cars
The best cars in the World Solar Challenge average about 100 km/h, for 9 hours a day, using the full days' sunlight. (They start charging at dawn, finish at dusk, but Challenge rules only allow them to drive for 9 hours a day.) So that's 900 km per day, every day, off 6 square metres of cells. A parking space is at least 12 square metres.

Comment: Self-reproducing (Score 1) 83

by Ronin441 (#43971103) Attached to: The Turbo Entabulator: A 3D-printed Mechanical Computer

The RepRap project is an initiative to develop a 3D printer that can print most of its own components.

Until now, RepRap have been stymied by an inability to print any of the systems that control the printer. But, no longer! Simply print a mechanical computer to drive your 3D printer, and the goal of a self-reproducing device will be fulfilled!

Might be large, though.

Comment: Re:I travel with 2 27" apple cinema displays... (Score 1) 141

by Ronin441 (#43887241) Attached to: Ask Slashdot: Portable High-Resolution External Displays?

relative light weight

In my experience, custom-made transit cases of this style (plywood panels with thin aluminium sheets over them and aluminium corner and edge pieces) are heavier and more expensive than a similarly sized Pelikan cases.

If you left out the plywood and used something like Ayres composite panels, you could save a lot of weight, though.

Comment: OKCupid does something like this (Score 1) 193

by Ronin441 (#43051959) Attached to: The Real Reason Journal Articles Should Be Free

Dating site OKCupid does something like the negative of this:

  • Anyone can become a user.
  • Any user can post a profile, photo, etc.
  • Any user can flag a profile, photo, etc. as inappropriate.
  • Flagged content goes to a subset of those who have volunteered as moderators. (Only experienced users may moderate.)
  • Moderators mark the content either for deletion or retention.
  • Items marked by enough moderators for deletion are given a second look by OKCupid employees, then deleted where appropriate.

This is not terribly different from the moderation system here at /. in that all content is initially visible and is only moderated after publishing. But it's similar to the academic case in that items go to anonymous peer review and then to a non-anonymous editor for final decision.

Comment: Re:Killing anonymity (Score 1) 88

by Ronin441 (#41728257) Attached to: Aussie Researchers Crack Transport Crypto, Get Free Rides

Perth SmartRider does indeed use MiFare Classic, and the cards are indeed insecure. But there's some server-side smarts which will (eventually) notice a cloned card, and deactivate it. I expect it also (eventually) notices if you top up your card yourself for free.

The idea is that although the system can be exploited at a small scale, it isn't worth the hassle. Provided their server-side stuff prevents exploits going commercial and becoming widespread, it's good enough.

The best laid plans of mice and men are held up in the legal department.

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