EE Times Under the Hood - June 23, 2008 - (Page U6)

UTH0623pg4-10.qxd 6/13/08 5:45 PM Page 6 under the hood: FEATURE Maximum power solar converter www.eetimes.com • www.techonline.com that it be easy to assemble on the space station and that it work with simple, inexpensive ground receive equipment, so that teachers and hobbySolar panel Current sense Boost supply Output ists could readily track the signals. All they should have to do would be to download free software that let them track the audio and deciOvervoltage pher the audio-encoded images. Voltage sense Oscillator protection SuitSat-1 comprised a controller box with a control printed-circuit board, dc/dc converter PIC16F690 and EMI filter. This connected to a separate radio Max. power Programmable box that used an off-the-shelf Kenwood TH-K2 algorithm voltage reference amateur handheld two-way VHF radio with an external quarter-wave, ground-plane antenna. Source: Microchip Technology The controller also connected to a switch box with one power and two timer switches that were used to start the system upon deployment. The whole worldwide to pursue careers in science, technology, engisystem was powered by the suit’s own three, very expenneering and math through amateur-radio communications sive but high-power-density 28-volt silver-oxide batteries. opportunities with the space station on-orbit crew. The controller board was where the messages were McFadin was calling in the wake of an AMSAT Symstored and where temperature and voltage monitoring posium/ARISS International Partner meeting at which it was decided to convert an old Russian Orlan space suit into took place. At its heart was the PIC18F8722, a 64/80-pin microcontroller with 1 Mbit of enhanced flash, on-board a satellite by outfitting it with telemetry equipment and 10-bit analog-to-digital converter and the company’s antenna—and to toss the suit out of the space station. nanoWatt technology. Another reason that processor got The plan, code-named SuitSat, called for the novel picked was its ability to handle voice signals encoded using “satellite” to transmit spoken greetings from children in adaptive pulse-code modulation (ADPCM). Those signals multiple languages, as well as slow-scan TV images encodwere stored on an 8-Mbit SPI serial flash chip from SST ed in audio signals and some spoken telemetry, such as (the SST25LF080A), programmed via an RS-232 interface, elapsed time, temperature and battery voltage. McFadin and a MAX3232 RS-232 level shifter from either Maxim or was calling Microchip Technology Inc. to see if a PIC Texas Instruments (dual sources). microcontroller could handle the job. The ADPCM signal was output from the microconIt seemed simple enough, and so a small team from troller to an MCP6022 op-amp-based, 4-kHz low-pass filMicrochip volunteered to help out. “We got into it thinking ter, and from there passed on to the radio, which transit’s easy,” said Steven Bible, technical staff engineer at the mitted at 145.99 MHz. Also on the board were an Chandler, Ariz., company. “Kind of like a high-level science MCP9800 SPI temperature sensor and three MC14541 fair project.” They were mistaken. programmable timers. What the Microchip engineers didn’t fully appreciate at the time was that extreme environmental and safety issues Safety first would challenge them at every step of the design. With a The inclusion of timers on the control board underscored vacuum to deal with, they learned about the implications the biggest problem the designers faced: safety. “We had to of outgassing and about handling thermal hot spots with deal with NASA safety people,” said Bible. “It was mindno airflow. They also learned how to avoid the Fermi boggling.” Each aspect of the design had its own documenregion to prevent arcing, how to handle thermal extremes, and what do about ionizing radiation. They studied power- tation: snag hazard, outgassing hazard, electric shock and RF hazard. To handle the latter, the timers were used to optimization techniques for system longevity, and with no gravity for stability, they found out the hard way what a tumbling antenna does to radio reception. The experience proved so interesting that the engineers SuitSat-2 software-defined transponder (SDX) enthusiastically signed up for SuitSat-2. Leveraging their acquired knowledge, the team has already developed a IF IN QSD new solar-conversion technique for the follow-on satellite that will extend system life to months instead of weeks. 10.7-MHz IF Codec dsPIC33F SPI to They have also crafted a software-defined, full-duplex IHU radio with a better antenna for two-way communication IF OUT QSE and more-refined control. Electronics the easy part From a schematic-diagram point of view, the original SuitSat-1 system and its electronics were fairly straightforward. According to Bible, the main design parameters were I 42.8-MHz LO LO Source: Microchip Technology 6 Electronic Engineering Times, TechOnline | June 23, 2008 http://www.eetimes.com http://www.techonline.com

Table of Contents Feed for the Digital Edition of Under the Hood - June 23, 2008

Under the Hood - June 23, 2008 Extreme Design: SuitSat Pushes Desigers' Limits Evolution of the Smart Phone Mature Devices get Rolly Rocking GPS: Garmin Nuvi 750 vs. HP iPaq 310 Inside the Sony OLED TV Multizone Dgital Audio Flip Ultra Camcorder - An Ode to Clean Design Robot Guitar Tunes Itself E-book is a Sight for Sore Eyes Scientific Calculator Boils Down to Two ICs $100 BOM Eludes First OLPC Laptop 45 nm: What Intel Didn't Tell You Next Step in NAND Flash Evolution Surveillance on a Shoestring Hot 3G Phone Owes Debt to Analog SecurID Fob: Single-Chip Safety Net

Under the Hood - June 23, 2008

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