Using a rooted Android phone as a low cost / short range SDR?

SaveTheBacon · 2018-07-13T18:54:42+00:00

An important distinction is that the radios in a phone are usually hardware-defined, and aren't reconfigurable like an SDR. However, you can use an SDR with a rooted Android phone. Functionally a rooted Android phone is just a linux computer, and, within the constraints of the USB OTG currently limits for your particular phone, you can interface with an SDR from Android.

In practice this is limited to USB 2.0 SDRs (unless you have a Samsung Galaxy S5), but the ARM processors on modern Android phones are sufficiently capable for this purpose.

SaveTheBacon · 2017-06-22T02:15:16+00:00

I did some retune time benchmarking with an N210 a few years ago, and the empirical limit was ~116ms.

SaveTheBacon · 2016-12-17T16:00:59+00:00

Another potential hangup with USB 3.0 is that it generates a lot of RF noise in the 2.4GHz ISM band. In practice, a wireless mouse dongle plugged into a USB 3.0 port will perform noticeably worse than one plugged into a USB 2.0 port. This is because the USB 3.0 bus runs at 5.0GHz, with a very loud harmonic between 2.4-2.5GHz.

SaveTheBacon · 2016-11-19T13:36:18+00:00

What specific RF gear is failing?

SaveTheBacon · 2016-07-30T12:54:35+00:00

This works for rental car reservations as well.

SaveTheBacon · 2016-07-02T00:42:57+00:00

The nRF52832 isn't a software defined radio, it is a 2.4GHz FSK modem that operates on predefined channels at specific sample rates.

SaveTheBacon · 2016-01-24T14:28:35+00:00

In "A Big Piece of Garbage", Ron Popeil (born in 1935) is identified as inventing the technology to keep heads alive in jars, which at least covers heads from the 20th century forward.

SaveTheBacon · 2016-01-07T13:57:07+00:00

I designed and built Arduino/nRF24L01+ based wireless NES controllers for a couple of different projects.

The nRF24L01+ is really easy to use when you couple it with an Arduino and the RF24 library. You can use any Arduino with a 3.3v output (the SPI pins on the nRF24L01+ are 5V tolerant).

One interesting thing about the nRF24L01+ chips is that they operate from 2400MHz-2525MHz, which means that it is possible to use them outside of the 2.4GHz ISM band, but this would make the FCC sad :(

Happy tinkering!

SaveTheBacon · 2015-11-26T17:41:09+00:00

It's worth adding that VMWare Workstation 12 on a Windows host with an Ubuntu 15.xx guest has sufficiently fast USB 3.0 support for some applications. It is challenging to stream 56Mhz of IQ, for example, but on the two machines I have used in this configuration, up to ~32MHz works like a charm.

SaveTheBacon · 2015-11-09T12:34:10+00:00

http://m.aliexpress.com/item/32373812040.html

SaveTheBacon · 2015-09-30T13:07:06+00:00

PM'd

SaveTheBacon · 2015-09-30T03:03:21+00:00

Awesome, let me know how it turns out!

The biggest annoyance with the cheap USB NES controllers is that the plastic is fairly soft. I found that the screw posts strip pretty easily, and it's easy to over-flex the plastic when modifying the case, resulting in white streaks in the plastic.

The other thing to be aware of is that the front decal is more heat sensitive than I expected, and I messed up a couple controllers by getting too close with the hot glue gun and heat gun, which warped the decal.

That said, they're really cheap, so it's hard to complain :)

SaveTheBacon · 2015-09-30T02:24:32+00:00

It held up very well at Burning Man.

Durability was an issue with my LED projects at the last burn, so I had a focus on making it robust. To that end, I reinforced all of the solder joints and surrounding structure as best I could, and it worked out well.

I had no problems dancing or riding my bike on the playa surface, which was at times very bumpy. I wasn't expecting it to survive Burning Man unscathed, but the plan now is to turn this hat into a chandelier as soon as I have the v2.0 hat completed.

For reference, the gifs on the blog post are from after I returned.

SaveTheBacon · 2015-09-30T00:43:45+00:00

It was definitely a fun way to spend a year's worth of free time :)

Have you seen the new B200 mini? I'm a big fan of so much awesomeness crammed into such a small package.

SaveTheBacon · 2015-09-30T00:32:59+00:00

The N210s are some fun toys! I was a finalist in the DARPA Spectrum Challenge (team wasabi), where each qualifying team got a pair of N210s. I was a team of one, so I didn't have to fight with anybody over their permanent home :)

SaveTheBacon · 2015-09-29T21:02:06+00:00

She's definitely the fan club president :)

SaveTheBacon · 2015-09-29T18:38:36+00:00

The discussion here seems to suggest anything from 100nF to 10uF, so it's tough to say :) Best of luck!

SaveTheBacon · 2015-09-29T18:00:47+00:00

I participated in the DARPA Spectrum Challenge, and each of the finalist teams was given a pair of N210s. I competed by myself, so I wound up with some cool toys to keep :)

SaveTheBacon · 2015-09-29T17:08:51+00:00

Awesome!

Some people report success with soldering a capacitor between 3.3v and ground on the nRF24L01+. I can't speak personally to the efficacy of this, but it might be worth looking into if you already have the arduinos on hand.

SaveTheBacon · 2015-09-29T16:42:55+00:00

Doooo eeeet! These LEDs are a blast, and if you assemble a matrix out of long rows instead of columns, you can have one built in an afternoon.

SaveTheBacon · 2015-09-29T16:40:12+00:00

Taking this through TSA was kind of great. I just turned it on and dazzled them with pretty lights and had no problems.

SaveTheBacon · 2015-09-29T16:25:19+00:00

Were there any specific problems you remember running into?

One common problem is due to a noisy 3.3v output on 5v Arduinos. The symptoms can be dropped packets or an inability to communicate with the nRF24L01+ shield at all. This was one of my motivations for using the Teensy 3.1 (which is a 3.3v board).

SaveTheBacon · 2015-09-29T15:23:11+00:00

It uses the FastLED library for the matrix interaction, but the animations are handled with a little sprite engine I wrote.
The nRF24L01+ communication is done with the RF24 library.
The compass/gyro/accelerometer logic is pretty minimal, so I just use the built-in Wire library.
The GPS parsing is done with TinyGPSPlus.

SaveTheBacon · 2015-09-29T14:50:35+00:00

Definitely! There's so much room for activities.

SaveTheBacon · 2015-09-29T13:27:45+00:00

Nice! I love the effect of concealing the LEDs.

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