Hackaday Links: July 20, 2012

Hey, it’s the 43rd anniversary of men first walking on the moon. Here’s some stuff we found to celebrate that. Fun trivia: for Apollo 11, [Neil] and [Buzz] didn’t go more than 200 feet from the LEM.

This is so incredibly sad

Remember Heathkit? A lot of cool kit-based electronics came from them. They’re out of business, but you can get all the Heathkit swag you can imagine from the repo man. A ton of stuff from the old Heathkit headquarters is being auctioned off in Byron Center, Michigan this Tuesday, July 24. Notable lots include a HE-Robot and a nice pair of o’scopes. If someone wants to pick up one of the catalog lots for us, we’d be thankful.

Troll Physics: ‘What is with this guy’ edition

We’ve seen [Fredzislaw]’s LED trickery before. The first time was a crazy 3 LED circuit, the reveal of which showed two AC power supplies in a battery connector. This time, [Fred] has two switches and an LED. Turn one switch on, the LED lights up. Turn that switch off and flip the other one, the LED still lights up. Turn both switches on, the LED goes off. Your guess is as good as ours.

Prototyping with a key fob remote

[Gary] wrote in to tell us about the dev board he’s been working on. It has either a PIC or AVR on the back side, broken out into 0.1 inch headers on the front. There’s a small solderless breadboard and an on-board RF link that uses a five-button key fob remote. Seems very useful, no matter what side of the PIC/AVR holy war you’re on.

Consumer Alerts: Software defined radio

Over on the RTLSDR subreddit, [photoscotty] bought this TV tuner dongle from Deal Extreme and received the inferior EZTV645 tuner. Unsurprisingly, Chinese manufacturers will just grab whatever is available, put it in an envelope, and ship it off on a slow boat from China. [photoscotty] is trying to return his dongle to DX, but until Sparkfun or Adafruit start selling these things (yes, there’s a market now get on it) you’ll have to be careful out there.

Wouldn’t this feel terrible against your skin all day?

[Colin] printed a watch band on his Makerbot. Apparently Shenzhen humidity didn’t play nicely with his nylon strap, so [Colin] made his own out of plastic. It’s flexible and has a neat looking clasp, as well as an awesome demo for what a 3D printer can actually do. Thingiverse files here.

13 thoughts on “Hackaday Links: July 20, 2012

  1. The LED trick is less complicated this time and seems pretty simple.

    First the LED is actually two LEDs – http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/MV5094A,5491A.pdf.

    The battery or battery lead is an AC generator.

    Each switch is actually and switch and diode in parallel and then a reverse diode in series. With the two switches having opposite diodes.

    So when switch A is on the current is passing through first the resistor, then the closed switch, the hidden series diode, one of the LEDs, and finally bypassing the last switch through the hidden parallel LED.

    When both switches are off the hidden parallel diodes are the only path and since they are opposite they won’t let current flow.

    When both switches are on the hidden series diodes are the only path and again opposites.

    1. That last part isn’t quite right, with both switches on it would allow both phases through not neither.
      My AC circuits knowledge isn’t quite there, but what if there is an inductor in line (perhaps the fake looking resistor). When only one phase is passing through, the inductor charges up a little bit and allows the signal. When both phases are on the inductor would act as a filter, I think, and not allow any of the signal.

      Ghetto Schematic – https://dl.dropbox.com/u/6704988/website/Media/GhettoSchmatic.png

    2. Troll Physics – I haven’t seen the video, but the description sounds like just a pair of regular “three way” switches, but using some extra diodes in the switches to avoid having to have an extra wire.

      Inside each switch you have a couple of diodes (one connecting the switch “on” terminal to the output, going one direction, and one in the opposite direction connecting the switch “off” terminal to the output).

      As noted above the input is AC, the LED is 2 leds in opposite directions.

      So when switches are in opposing configuration (one “on” other “off”) no current flows because of the opposing diodes in the switches. When in matched configuration (both “on” or “off”) then the diodes in switches are in same direction, and one or the other of LEDs lights.

  2. Alas, the Heathkit auction is as-is-where-is, and the “where” is not in proximity to my “where”. : (

    (I’m one of those old farts still using the Heathkit whose build taught me to solder.)

    1. I had the same thing. I got a 645 too. it still works with RTLSDR but if you want a proper 668 there is a seller on eBay in the states called “nooelec” (http://myworld.ebay.co.uk/nooelec/?_trksid=p4340.l2559) who sells the one with the EC4000. He claims to have a LOT of the 668’s, I can also vouch for him as I got my second one from him after DE sent me a 645. He also mentioned that the company that makes the EC4k chip is up for sale or something and that chip is becoming hard to get hold of, hence I suspect why deal extreme is sending out different sticks.

  3. Ugh. I have had nothing but bad experiences with Deal Extreme. One does figuratively get what one pays for in this case. . . I am so over cut rate direct from Asia electronics.

    – Robot

  4. I recently purchased a Newsky SDR dongle off Amazon for $30. Probably paid too much, but it was still a better deal than what these things are going for on eBay right now. It works great, now I just need to make a decent antenna.

  5. lol yeah nice try HaD. Only adafruit and sparkfun make electronics that sell and ship reliably… I feel like we are returning to the Arduino marketing clone wars. Finish the RasPi campaign and then start back on this once the chip co goes under completely.

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