Passive Filters, Data Transmission and Equalization Oh My!

[Shahriar] is back with a new “The Signal Path” video. It has been a few months but it is okay because his videos are always packed full of good information. Some new equipment has been added to his lab and as an added bonus a quick tour of the equipment is included at the start, which is great if you like drooling over sweet machines.

The real focus of the video is high speed data communications, getting up into the GHz per second range. [Shahriar] covers filtering techniques from simple RC low pass filters to pretty complex microwave filters. Explaining frequency and time domain measurements of a 1.5Gbps signal through a low bandwidth channel. He also shows how equalization can be used to overcome low bandwidth limitations.

It is an hour long video jam packed with information, so you might want to set aside some time and have a pencil on hand before going in. It is well worth it though, so join us after the break.

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Kitchen Hacks: Microwave plays YouTube videos matched to your cooking time

Behold the uWave, a microwave oven that plays YouTube videos while it cooks. [Kevin] and three classmates at the University of Pennsylvania developed the project for the 2011 PennApps hackathon. It uses a tablet computer to replace the boring old spinning food display microwaves are known for. Now, an Arduino reads the cook time and sends that information to a server via its Ethernet shield. The server then searches YouTube for a video that approximately matches the cooking time, then pushed that video to the tablet to start playing. The video demonstration embedded after the break shows this, as well as the tweet that the machine sends at the beginning of the process.

It’s an interesting concept, and we think the code used to push a video to the tablet has a lot of other applications (we’re keeping this one bookmarked). On the other hand, we wonder how long it will take for public microwaves to become ad-supported? We’re thinking it’s hard for companies selling antacids, acid reflux medicine, Cup ‘o Soup, and Hot Pockets to resist this opportunity.

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Repaired microwave keypad looks as good as new

microwave_keypad_repair

Instructables user [Rohit] had an out-of-warranty microwave with a broken membrane keypad. Much like our friend [Alexandre] from Brazil, he found the cost of replacement parts beyond reasonable, so he had to find a way to repair it instead.

He disassembled the front cover of his microwave to get at the main controller board. Once it was detached, he removed the keypad’s cover to get a closer look at the matrix underneath. While taking notes on how the matrix was wired, he found that some keypad traces connected to other traces rather than buttons. He says that they are likely used by the microwave to detect that the keypad is present, so he made sure to short those traces out on the controller board when he wired everything back together.

He replaced the aging keypad with microswitches, but rather than mount them on the front panel of the microwave, he drilled holes for each switch so that he could mount them inside the face plate. Once everything was wired and glued in place, he re-mounted the keypad’s cover. Now the microwave looks stock but has firm, reliable, user-serviceable buttons that are sure to last quite a while.

Repairing a broken microwave keypad

microwave_keypad_fix

[Alexandre Souza] needed a microwave pretty badly, but he didn’t have a lot of cash on hand. He located one for a great price, but once he got home he found that things weren’t working quite like they should be (Google translation).

After some investigation, he narrowed the problem down to a bad keypad membrane. Unfortunately for him, this model of microwave was never sold in Brazil (who knows how it got there) and the only membrane he could track down had to be shipped in from the US at a cost of $80.

Rather than pay such a high price for a simple membrane, he opted to fix the microwave himself. He dismantled the control panel and thoroughly traced the keypad matrix to get an understanding of which pins toggled which functions. With a piece of protoboard and almost two dozen push buttons in hand, he built his own keypad and wired it directly into the microwave’s control board.

With labels written in marker it might not be the nicest looking thing you have ever seen, but it works a treat and is a great money-saving hack.

HERF gun zaps more than your dinner

herf_gun

Instructables user [Jimmy Neutron] had an old microwave sitting around and figured he might as well gut it to build a high-energy radio frequency (HERF) gun.

The concept of a HERF gun is not incredibly complex. Much like your microwave at home functions, a high voltage power source is used to drive a magnetron, which produces micro wave radiation at 2.45GHz. These waves are then guided away from the magnetron using a waveguide, towards whatever the target might be. These waves then energize the target in a similar fashion as the water molecules in your food are energized during cooking.

[Jimmy] has not quite finished his HERF gun as he still needs to build a waveguide for it and then safely mount it for use. In the meantime, check out the pair of HERF guns we found in the videos below.

As a parting note, we must stress that building a similar device is dangerous, very dangerous – especially if you do not know what you are doing. Microwaves contain high voltage components, and exposure to microwave radiation can be deadly under certain circumstances. Stay safe!

Looking for more microwave fun? Check these out!

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Building linear amplifier prototypes

We know way too little about this subject but hopefully [Bob4analog] helped us learn a little bit more this time around. He’s building his own linear amplifiers on what looks like sheets of MDF. This is an evolving design and the two videos after the break show two different iterations. He’s salvaged several components, like transformers from microwaves, as well as built his own components like the plate choke to the right of the tubes in the image above. In standby, the amp sits at 2800 volts, warming the filament before the unit is switched on.

So what’s he got planned for this? Good question, but it appears that there’s more than enough power to drive a long-range transmitter.

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Halloween props: flying crank ghost

flying-crank-ghost

[Jake's] projects have become regular features here on Hack a Day. He keeps the Halloween hack-fest rolling with his Flying Crank Ghost. For the ghost he used a store-bought skull but sculpted some hands himself out of Styrofoam. The body is fashioned from coat hangers with a bit of creepy fabric draped over the hole thing to complete the look.

He added some very convincing motion to the ghoul using a salvaged microwave turntable motor. The motor is mounted in the center of a two crossed boards, and has an armature attached to it. Three strands of monofilament attach to the end of the armature, run through eyelets on the ends of the crossed boards, then attach to the head, and each arm. When the motor is turned on, the armature turns, moving the head and hands up and down at different rates. Take a look at the embedded video after the break to see the final product.

[Jake] does mention that the motor he used is a bit underpowered. We figure this only needs to hold up for one night, so dig through your junk bin and see if you can throw one of these together in a few hours.

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