The In-Circuit SD Card Switch

SDISP

For nearly every problem, it’s possible to engineer a solution, even if you’re dealing with an extraordinarily niche problem that might only apply to yourself. [Joel] wanted to be able to program the microSD card in his BeagleBone with a new bootloader or file system without removing the SD card from the target board. This is a peculiar requirement, and it’s highly doubtful a product or even a circuit exists for such a function. This meant [Joel] would need to roll his own board to accomplish the task.

The board is remarkably simple, housing a single microSD socket, two expansion headers for a microSD sniffer for a computer and an embedded board, an FTDI header, and a pair of 4-bit multiplexer/demultiplexers. The operation of the device is fairly straightforward: send a signal down the FTDI cable, and the board switches the onboard SD card from one device to another.

[Joel] has a video of his screen that shows him pulling off in-circuit SD card reading and writing. You can check that out below.

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DIY Pressure Plate Switch for your Haunted House

Pressure Plate

Yes, its Halloween time again and the hacks are going to be crawling out of the woodwork for the rest of the month. [Rich Osgood] is off to a good start promising one hack every week until Halloween. Judging from this first project, a DIY pressure plate switch, we think there’s going to be a common theme to follow. [Rich] constructs his pressure plate for almost no cost using cardboard, tinfoil and duct tape. It couldn’t be easier, so make lots of these if your haunting project requires pressure plate triggers to activate any spooks. Judging by the cardboard construction it’s likely they will fail after multiple uses, but you can switch one out quickly requiring only two hookup wires and a bit of tape.

Hopefully we aren’t stealing [Rich’s] thunder by recommending using Xbee wireless remote sensors to covertly monitor guests or trigger spooktacular scares.

We will be keeping an eye out for [Rich's] follow-up Halloween hacks. Join us after the break to watch the tutorial video on making homemade pressure plates.

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Rotary phone museum exhibit

dial-telephone-museum-exhibit[David Burroughs] wrote in to share this dial telephone museum exhibit he built and we’re glad he did because we love interactive museum hacks. He mentions that it’s not really tied to the theme of the Roads and Rails Museum in which it’s installed. But when we think of railroad history we also think of telegraph. And that’s just a hop, skip, and a jump from telephones.

The display allows museum goers to play with the rotary dial on the phone. The box next two it contains a 10-position relay increment switch. So each pulse from the dial increments the switch. There’s a satisfying click, a moving arm, and different colored LEDs which highlight the inner workings. An Arduino board monitors the phone, displaying the dialed number on a seven segment display then incrementing the relay.

We figure the interesting part is to see that telephony used to use mechanical switching like this. But the video below includes a story about the kid who asked how you carried this phone around. This brings to mind the phrase “hang up the phone”, which doesn’t have the same literal meaning it used to.

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Viscerally pleasing electromechanical doorbell

steam-punk-doorbell

Sure, we could just slap the steam-punk label on this doorbell hack, but we think that cheapens it. The rig uses a combination of mercury switch and creative mechanics to form a doorbell. And we think it goes beyond aesthetics to a statement of who you are starting with the front door of your house. No wonder [Nick Normal] has moved it along with him from home to home over the years.

The portion to the right is the ringer itself. Pulling on the lever moves the chain through an eyelet to affect the mercury switch mounted above. That switch completes the circuit which drives the motor on the “bell” unit. We use quotes because instead of ringing a bell it’s striking the large valve control wheel which looks like it came straight from the same industrial plant where The Joker took his unfortunate fall into a vat of acid.

This certainly gives you something to aspire to. And if you think you’ve already achieved a doorbell setup on similarly-geeky footing why haven’t you tipped us off about it?

Hacking a PAL SNES to output 50Hz or 60Hz with a single switch

snes-pal-ntsc-mod

[Derecho] grabbed a PAL format Super Nintendo but wanted to make it play nicely with a 60 Hertz NTSC screen. His hack added a single switch to choose between 50 Hz and 60 Hz.

Take a look at the image above to see his alterations to the mainboard. The jumpers soldered to the two chips at the top are by far the trickiest part of the project. Each of the pins he soldered to needed to first be lifted from the PCB pad so that they no longer make contact with the etched traces. The technique he used involves heating the pin with an iron, then gently lifting it with a pin or a razor knife/blade. If you’ve got some experience populating SMD boards with a handheld iron this shouldn’t prove too difficult. The rest of the hack involves adding a 3-position switch (along with a 2k2 resistor) to choose between output modes based on what format game is being played.

Simple to build programmable foot switches

programmable-footswitches

Your hands do a lot of work between the keyboard and the mouse, why the heck are you letting your feet be so lazy? [Dossier van D.] is putting an end to the podiatric sloth. He built this set of three foot pedals which have gone through two versions of functionality.

The buttons themselves are made from a base plate of plywood with a smaller piece on top for each ‘key’. The two parts are separated with some foam carpet pad, with a tactile push button in between to register a click. The only thing we’d change about this is adding a couple of wooden spacers next to the switch so that accidentally sanding on a button doesn’t break that electronic component.

Originally each button was soldered to a gaming controller. This worked just fine using button mapping, but recently [Dossier] made the switch to using an Arduino Leonardo. This is a perfect choice. Unlike input devices made with older Arduino versions the Leonardo board can natively register as a keyboard, making it a snap to programmatically map any key to the switches.

If you like this project you should check out [Dossier's] foot mouse as well.

Cracking open a 24-port switch so you don’t have to

hp-procurve-ethernet-switch-teardown

[Kenneth Finnegan's] post about this 24-Port HP ProCurve 2824 Ethernet Switch teardown was a delight to read. He’s taking an introduction to networking class at California Polytechnic State University. One of their labs included virtual machines shooting thousands of new MAC addresses at the thing all at once. Despite it’s ability to switch data at a blazing fast rate, it’s ability to deal with that many new hardware identifiers was less than impressive. He wanted to find out why and it just so happened he had one of these in his parts bin at home (which he refers to as if it’s a high-powered RPG character).

The mainboard is divided into three major blocks: the power supply, the switching hardware, and the processor that makes this a manged switch. Although he covers all of these pieces (and the switching stuff is very interesting to learn about) it is the processor section that was causing the aforementioned slowdown. It’s a 266MHz PowerPC chip with a measly 64 MB of RAM. Of course this doesn’t need to be any more powerful since all traffic from previously ‘learned’ MAC addresses gets handled by the switching block and never touches the processor portion.

Don’t miss the end of his post where he discusses how the filtering caps, and semi-isolated ground planes help to tame the beast created from all of this high-speed switching.

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