Retrotechtacular: Ma Bell’s Advanced Mobile Phone Service (AMPS)

This gem from the AT&T Archive does a good job of explaining the first-generation cellular technology that AT&T called Advanced Mobile Phone Service (AMPS). The hexagon-cellular network design was first conceived at Bell Labs in 1947. After a couple of decades spent pestering the FCC, AT&T was awarded the 850MHz band in the late 1970s. It was this decision coupled with the decades worth of Bell System technical improvements that gave cellular technology the bandwidth and power to really come into its own.

AT&T’s primary goals for the AMPS network were threefold: to provide more service to more people, to improve service quality, and to lower the cost to subscribers. Early mobile network design gave us the Mobile Service Area, or MSA. Each high-elevation transmitter could serve a 20-mile radius of subscribers, a range which constituted one MSA. In the mid-1940s, only 21 channels could be used in the 35MHz and 150MHz band allocations. The 450MHz band was introduced in 1952, provided another 12 channels.

repeated channelsThe FCC’s allocation opened a whopping 666 channels in the neighborhood of 850MHz. Bell Labs’ hexagonal innovation sub-divided the MSAs into cells, each with a radius of up to ten miles.

The film explains quite well that in this arrangement, each cell set of seven can utilize all 666 channels. Cells adjacent to each other in the set must use different channels, but any cell at least 100 miles away can use the same channels. Furthermore, cells can be subdivided or split. Duplicate frequencies are dealt with through the FM capture effect in which the weaker signal is suppressed.

Those Bell System technical improvements facilitated the electronic switching that takes place between the Mobile Telephone Switching Office (MTSO) and the POTS landline network. They also realized the automatic control features required of the AMPS project, such as vehicle location and automatic channel assignment. The film concludes its lecture with step-by-step explanations of inbound and outbound call setup where a mobile device is concerned.

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Frappé Coffee Robot Offers Automated PIC-Me-Up

Although [Giorgos Lazaridis] has graced Hackaday several times, we’ve never covered the build of his frappé machine which reader [Jim] encountered after searching for information about the PIC16F1937. His site shows the build as in-progress, but he definitely has a working prototype here, and it’s definitely awesome.

Frappé coffee is made by mixing spray-dried instant coffee, a small amount of cold water, and sugar to taste in a manual shaker or a milkshake machine that uses a single beater. More water and/or milk is added as desired to top off the glass. The method was invented by accident in Thessaloniki, Greece, and has become quite popular.

In addition to sixteen pages of detailed build logs, [Giorgos] shot videos that demonstrate each of the modules that make up the machine. The operator puts a glass in a holder attached to a turntable. It moves first to the coffee and sugar dispenser, which fall through the same easily removable funnel. The next stop combines the add-water-and-beat steps beautifully. A length of hose strapped to the beater’s housing dispenses the initial cold water base. Then, the beater lowers automatically to beat the mixture. After mixing, the beater is drawn back up an inch or so, and more water is dispensed to rinse it off. Then the beater is fully withdrawn and the glass is filled the rest of the way. The final stop for the frappé is essential to the process: a bendy straw must be added. This is vitally important, and [Giorgos] handles it admirably with a stinger that shoots a straw into the glass.

[Giorgos]’s coffee robot is built around a PIC16F1937. He rolled his own PCB for the motherboard and each of the machine’s modules. There is a lot of logistical ingenuity going on in this project, and [Giorgos]’ build logs convey it all very well. Be sure to check out [Giorgos]’ machine in action after the break. The full set of eight videos that shows each module and culminates in the one below is well worth your time.

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Retrotechtacular: The Construction of Wooden Propellers

During World War I, the United States felt they were lagging behind Europe in terms of airplane technology. Not to be outdone, Congress created the National Advisory Committee for Aeronautics [NACA]. They needed to have some very large propellers built for wind tunnel testing. Well, they had no bids, so they set up shop and trained men to build the propellers themselves in a fantastic display of coordination and teamwork. This week’s film is a silent journey into [NACA]’s all-human assembly line process for creating these propellers.

Each blade starts with edge-grained Sitka spruce boards that are carefully planed to some top-secret exact thickness. Several boards are glued together on their long edges and dried to about 7% moisture content in the span of five or so days. Once dry, the propeller contours are penciled on from a template and cut out with a band saw.

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Serial Surgery Saves Wacom Tablet from Landfill

Years ago, [Greg] got a Wacom Artpad II graphics tablet through Freecycle. What’s the catch, you ask? The stylus was long gone. When he found out how expensive a direct replacement would be, the tablet was laid to rest in his spare parts box. Fast forward a few years to the era of the phone-tablet hybrid and [Greg]’s subsequent realization that some of them use Wacom stylii. Eight bucks later, he’s in business, except that the tablet is serial. Wacom no longer supports serial tablets, so he had to convert it to USB.

With the help of the WaxBee project and a Teensy 2.0, he would be able to emulate an Intuous2 tablet by sniffing and re-encoding the packets.  Things got a little hairy when he went under the hood to remove the ADM202 TTL-to-RS232 chip with a Dremel—he accidentally gouged some of the pads it sat on as well as a few of the traces. Feeling frustrated, [Greg] took some high-res pictures of the board and posted them to a message board. As it turns out, those pictures helped him recreate the traces and get the tablet running. A little big of glue and tape later, he was in business. [Greg] even gave himself access to reprogram the Teensy.

hack.summit(); // a virtual dev conference

If you’d like to spend four days learning from and picking the brains of a big group of well-known developers and open-source wizards for the low, low cost of absolutely free, keep reading.

The hack.summit() conference is a live, global event put on by the  fine folks behind real-time programming assistance service hack.hands(). From December 1 to December 4, a wide range of speakers will present and answer democratically popularized questions over Crowdcast via Google+ Hangouts. Speakers in attendance include wiki inventor and Design Patterns pioneer [Ward Cunningham], Codeacademy founder [Ryan Bubinski], Google Glass creator [Tom Chi], Python Software Foundation’s [Alex Gaynor], and even the inimitable [Jon Skeet].

The goals for this conference are simple and admirable: to educate developers of all stripes about best practices, to encourage mentorship in the programming community, and to spread the joy of coding by supporting coding non-profits.

You can register for free simply by spreading the word through social media, but making a donation to the coding non-profit of your choice is definitely encouraged. There are many to great organizations to choose from such as  CoderDojo (an easy choice for us). A tidy summary of the event is available at the hack.summit() FAQ(PDF).

Retrotechtacular: The (Long, Arduous) Birth of a Tank

Throughout the 1950s and early 1960s, the United States Army provided regular status reports to both its interior members and the American public through a half-hour documentary television show called The Big Picture. Since the program was produced by the government, every episode immediately entered the public domain. This particular report tells the story of the T-48 project that culminated in the 90mm M48 Patton tank.

The film opens by providing a brief history of tanks and the lessons learned about them between WWI and the Korean War. The Army sought a more robust vehicle that could handle a wide variety of climates and terrain, and so the process of information gathering began. After a series of meetings at the Pentagon in which all parties involved explored every facet, the project was approved, and a manila folder was officially designated to the project and labeled accordingly.

vesselsWe then tour the R&D facility where new tank materials and components are developed and tested. It is here that the drive gears are put through their paces on a torsion machine. Air cleaners are pitted against each other to decide which can filter out the finest dust and sand. After careful analysis, different tank shell materials are test welded together with various, well-documented electrodes, and these panels are taken outside so their welds can be directly fired upon.

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100% DIY Intervalometer is 100% Awesome

It’s easy to tell from this process documentary that [Nagyizee] is not one to settle for prefabricated anything. He could have just bought some off-the-shelf DSLR intervalometer, but that would mean interfacing with someone else’s design through cold, soulless plastic.

[Nagyizee] wanted a one-of-a-kind tool built from the ground up. In addition to a timer, he was in the market for a light sensor and sound detection. He chose an STM32F100 ARM Cortex M3 running at 8MHz in the name of power efficiency and started designing the UI and firmware. A custom graphic library for the OLED display streamlines it even further. Once the schematic was finalized, [Nagyizee] devised a stylish and ergonomic wooden case to be milled with a tiny Proxxon F70.

With the enclosure decisions out of the way, he etched and drilled the PCB and placed the components. The light sensor needed a lens and a prism, so he made one from a 10mm LED body. Not one to miss a detail, [Nagyizee] also turned some buttons, hand painted them, and made a scroll wheel. He ends the video with a demonstration that proves it is quite capable. In addition to standard cable release mode, it handles long exposure times, sequential shooting, and capture on light, shadow, or sound. But wait, there’s more: [Nagyizee]’s creation combines modes with ease and grace.

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