Learning

So my next book, The Wild Half is out, as an ebook both at Amazon and Barnes and Noble.  It’s a Western, set in 1876 in Colorado.  This was the first historical that I completed, started as a teenager and finished when I was in my early 30′s.  I’ve finished it a lot more times since […]

[This post is originally from my blog. I'm bringing this spectrum analyzer to Darren Kitchen's Hak5 event at OMSI this Saturday (2013/05/25).] Here's some details of my radio spectrum analyzer hack at Maker Faire. But first, a quick video of the hack in action: src="http://www.youtube.com/embed/rmVu_mw3aJU" width="640"> Technical Details This project is built around the HackRF, a software-defined radio transciever. I programmed it to sample 20MHz of radio spectrum from an antenna, do a frequency analysis on the data, and display the results on a Noritake vacuum fluorescent display. I added the tuning wheel mid-afternoon on Sunday, and it really improved the interactivity of the display. It felt really cool to spin the wheel around and watch the spectrum scroll back and forth. Too bad I didn't capture that in the video... href="http://www.sharebrained.com/wp-content/2013/05/radio-spectrum-analyzer1-e1369184474197.jpg"> alt="" class="aligncenter size-medium wp-image-1009" height="560" src="http://www.sharebrained.com/wp-content/2013/05/radio-spectrum-analyzer1-e1369184474197-420x560.jpg" title="Radio Spectrum Analyzer at Maker Faire 2013" width="420"> The HackRF's microcontroller is an ARM Cortex-M4F + Cortex-M0 "dual core" chip. Both are running at 204MHz. The M4F has hardware floating point, which drastically simplifies the signal processing code. The ARM grabs 512 complex samples at a time from the radio analog-to-digital converter (ADC). It applies a href="http://en.wikipedia.org/wiki/Window_function">window function that reduces artifacts from sampling arbitrary chunks of a radio signal. The windowed samples are converted to href="http://en.wikipedia.org/wiki/Frequency_domain">frequency domain data through a 512-point href="http://en.wikipedia.org/wiki/Fft">fast-Fourier transform (FFT). The frequency data that comes out of the FFT (frequency vs. a complex vector) is converted to real magnitudes. I take the logarithm of each magnitude to get values vs. frequency that resemble href="http://en.wikipedia.org/wiki/Decibel">decibels. Then, I scale the log-magnitude data to fit nicely on the vacuum fluorescent display, which is 384 x 32 pixels. For each frequency in the scaled data, I render a bar into a frame buffer I maintain in RAM, using cute bit-shifting tricks. Then, I render marks at 1MHz intervals to provide a tick-mark scale on the display. In the left corner of the display, I render minimum and maximum sample buffer values for each of the two sampling channels -- this is so I can tell if I need to turn up or down the gain on the receiver. I draw the current tuning frequency in MHz at the center of the display. Lastly, I scan out each of the pixels, one byte at a time, into the VFD's parallel 8-bit interface, using the display's "Graphic DMA" mode. The optical href="http://en.wikipedia.org/wiki/Rotary_encoder#Single-track_Gray_encoding">quadrature encoder runs purely on interrupts. Whenever a positive- or negative-going edge is detected on either of the two optical sensors, an interrupt is generated. Based on the current and previous values of the optical sensors, the software (borrowed from PJRC's Encoder Library) decides if the wheel has moved, and if so, which way it has moved. Based on that decision, the tuning frequency is incremented or decremented. There was a hairy bit of wiring between the HackRF and the VFD. I needed to interface the HackRF, which is a 3.3 Volt device, to the VFD, which communicates at 5 Volts. So I needed to translate several signals between those two voltages. I had an old circuit board from my Robotron-FPGA project that did exactly that, for a completely different purpose. But with enough wires and headers and disgusting rewiring, I made it work. But it wasn't pretty. I had to keep poking it and twisting it, as some signals were intermittent and sometimes needed my help. The Faire Experience The HackRF can tune from below 10MHz (where it

Google's new music service offers a lot of eye candy to go with the tunes. The song selection of around 18 million tracks is comparable to popular services such as Spotify and Rhapsody, and a myriad of playlists curated along different genres provides a big playground for music lovers.

A billon-frames-per-second film has captured the vibrations of gold nanocrystals in stunning detail for the first time.

Physicists understand perfectly well why a fridge magnet sticks to certain metallic surfaces. But there are more exotic forms of magnetism whose properties remain unclear, despite decades of intense research. An important step towards filling these gaps comes now from Tilman Esslinger and his group at the Department of Physics.

(Phys.org) —Sometimes astronomy is like real estate—what's important is location, location, and location. Astronomers have resolved a major problem in their understanding of a class of stars that undergo regular outbursts by accurately measuring the distance to a famous example of the type.

Sugar isn't always sweet to German cockroaches, especially to the ones that avoid roach baits. In a study published May 24 in the journal Science, North Carolina State University entomologists show the neural mechanism behind the aversion to glucose, the simple sugar that is a popular ingredient in roach-bait poison. Glucose sets off bitter receptors in roach taste buds, causing roaches to avoid foods that bring on this taste-bud reaction. This aversion has a genetic basis and it eventually spreads to offspring, resulting in increasingly large groups of cockroaches that reject glucose and any baits made with it.

Here is my MRU video on precisely that topic. By the way, Brandon Dupont has done for us this excellent video on John Law.

Alton T. Young, known as “Al,” served as Erie County Sheriff for four terms, from 1948 to 1964. During Sheriff Young’s tenure, he was connected with several interesting ways to enforce the law. He formed the Erie County Sheriff’s Posse in 1962. Volunteers on horseback assisted in conducing manhunts and missing people searches. He also employed a canine “snooper,” which had been a gift from the Lorain County Sheriff. During the years that Sheriff Young was in office, his family lived in the Erie County Jail.Featured in the book Elected to Serve by Patty Pascoe, are several recollections of the children of Sheriff Young. His daughter recalled that the cooks who prepared meals for the prisoners also prepared meals for the Young family. When the stairs of the Sandusky Library were iced over, the Sheriff’s children would slide down the stairs on a sled. The Young children got to know the employees and the residents of the Erie County jail. They never felt they were in danger, even though they resided at the same place as those who had been incarcerated. In 1964, Al Young ran for a fifth term as Erie County Sheriff, but was defeated by Albert H. Hess. Mr. Young moved to Arizona, where he died at the age of 80. To read more about elected officials in Erie County, Ohio from 1838 to 2003, see Elected to Serve at the Sandusky Library.

Philosophy professor and author Simon Critchley recently held a suicide note writing workshop as part of a pop-up series dubbed the School of Death. ‘They are a last, desperate attempt at communication,” he said of suicide notes. “They are failed communication, in a sense’. Class included a spritely discussion about suicide and included a hands-on bit where participants penned their own suicide notes in 15 minutes and shared these aloud with their peers. Hmm, does seems more life-affirming than the subject matter would suggest. The post Believe it or not, there really is a suicide note writing class appeared first on Lost At E Minor: For creative people.