frequency hopping

2 Articles

Ask Hackaday: Frequency Hopping On The NRF24l01+?

March 21, 2017 by 50 Comments

We’ve seen a lot of hacks with the nRF24l01+ 2.4 GHz radio modules. The tiny chips pack a lot of bang for the buck. Since the radios can switch frequencies relatively quickly, [Shubham Paul] decided to take advantage of this feature to make a rudimentary frequency-hopping communications channel.

The code is actually incredibly simple. Both the transmitter and receiver simply scan up and down over the defined channels. Because the clock speeds of any given pair of Arduinos are likely to be slightly different, it’s not a surprise that the radios eventually drift out of sync. Right now, as a quickie solution, [Shubham] is using a serial-port resynchronization: both are connected to the same computer, and he just tells them to get on the same channel. That’s not a horribly satisfying workaround. (But it’s a great start!)

Keeping two radios that are continually swapping channels in sync is no easy task, but it could possibly be made easier by taking advantage of the nRF’s acknowledge mode. If the delay between a sent acknowledge message and a received one were constant, these events (one on TX and one on RX) could be used to re-sync the two hopping cycles. All of this would probably require more temporal resolution than you’re going to get out of a microprocessor running Arduino code, but should be possible using hardware timers. But this is pure speculation. We briefly looked around and couldn’t find any working demos.

So Hackaday, how would you remotely sync two nRF24s on the cheap? Or is this a crazy idea? It might help to make transmissions more reliable in the face of 2.4 GHz band interference. Has anyone implemented their own frequency hopping scheme for the nRF24l01+?

Citizen Scientist: Hedy Lamarr

November 16, 2015 by 97 Comments

For all the destruction and human misery unleashed during World War II, it was also a time of incredible creativity and ingenuity. In America, it was a time when everyone wanted to pitch in. Young men and women enlisted and were shipped overseas, and those left behind kept the factories running full tilt. Even Hollywood went to war, with its steady output of films that gave people a little glamour and provided an escape from the horror and loss of the war. Hollywood stars lined up to entertain troops and raise money for the war effort, and many joined up and fought too.

But one Hollywood star made an unconventional contribution to the war effort, and in the process proved that beauty and brains are not always mutually exclusive. This is the story of Hedy Lamarr, movie star and inventor.

“The Most Beautiful Woman in the World”

By the time she was 23 in 1937, Hedwig Eva Maria Kiesler was a genuine film star in her native Austria. She was also trapped in an unhappy marriage to a rich and powerful Austrian munitions magnate, Fritz Mandl. Hedy was miserable as a trophy wife, adorning the dining room as her husband entertained rich and powerful guests – including Mussolini and Hitler – over long dinners in one of his mansions. They dismissed her; clearly a woman so beautiful could have nothing else to offer, an empty head perched on a graceful neck. But she was far from stupid, and while her husband discussed business with the men who were building the Axis arsenal, Hedy listened and learned.

Continue reading “Citizen Scientist: Hedy Lamarr” →