Running OLinuXino-MAXI on Battery

Finally I've had some time to play with my new Olimex iMX233-OLinuXino-MAXI board, the board is similar to the Raspberry pi, almost the same size and cost, however, this one has an ARM iMX233 running at 454Mhz, less RAM and no GPU.

I played with the board for a while then I decided to test it using batteries, I found out that the USB/Ethernet physical is disabled when running on batteries ! After some digging around in the datasheet, there seems to be a way around this, by swapping two jumpers (3.3V_E and 3.3VIO_E) located near the reset button that control which DC-DC converter is used, the two possible configurations for those jumpers are:

1.  External DC-DC: 3.3V_E closed (soldered), 3.3VIO_E open (unsoldered/cut)
2.  On-chip DC-DC: 3.3V_E open (unsoldered/cut), 3.3VIO_E closed (soldered)

Note that the datasheet mentions that the maximum current that can safely be drawn from the on-chip convertor is 200ma and you need to make sure that you don't draw more than that, I'm not sure how exactly, but you should probably use one USB device at a time and either the USB or LAN.

It also mentions that the internal DC-DC makes the chip heat a little bit, so you may want to place a small heat sink on the processor.

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Portable SDR with Olinuxino for Tracking Wildlife

I was working on a project for a biologist friend of mine, that involved tracking RF tag implants on wildlife, using an SDR DVB-T dongle. He wanted a portable solution to be placed near the sprainting places of Otters(Lutra lutra), the main subject of the study, where they regularly come to deposit scent marks.

An RF tag is implanted on the animal which sends pulses on a frequency unique for each tag, this way we're able to tell them apart, this is what a cheap RF tag looks like,  this one has a frequency of 148.354Mhz

Software defined radio (SDR) became a bit more accessible recently, when a kernel hacker discovered that DVB-T dongles based on the RTL2832U chip can be used as a cheap SDR, since the chip allows transferring the raw samples to the host. Since the project was on a tight budget that seemed like a perfect solution...

The osmocom project provides a user space driver for the dongle, I started with pyrtlsdr, a Python binding for librtlsdr, and pylab for signal processing of the samples collected by the SDR, to compute and plot the PSD, that last spike corresponds to the signal of the RF tag above:

Finally, I ported everything to an olinuxino ARM-based board running Linux, a script runs on boot and logs the detected frequencies to file on SD card for later processing, the board still hasn't been tested in the field yet, I'm still working out some issues with the power management.

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