Monthly Archives: March 2013

Birth of the 32bit RS232 spectrum analyser

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It is time to revisit the RS232 spectrum analyser. Below is an image of some prototyping on a breadboard followed by a soldered working version including an SMA connection. The problem with the previous spectrum analyser was mainly in the computation of the frequency set registers which involved large 9 digit values, a hard feat for an 8-bit microcontroller. This time around a 32-bit microcontroller, the PIC32MX220B032 will be used. This will allow for a maximum clock frequency of 50MHz leaving the radios internal frequency settling time as the only limiting factor to the spectrum analyzer sweep time. The proposed specification for this spectrum analyzer is as follows:

  • Bandwidth 260MHz – 960MHz (Realistically about 150MHz according to the input filter of the RFM22B model used)
  • 2ms per sample
  • Sweep and Discrete measurement modes
  • Calibration mode (Calibrates the device with the help of a sweeping signal generator)
  • Wireless trace measurement (Two devices needed, one as a base station)
  • SD card for onboard storage and buffering
  • Connectivity – FTDI cable and rasberrypi GPIO connector header
  • Form factor: 1 square inch

    Breadboard prototyping of the 32bit spectrum analyser

    Breadboard prototyping of the 32bit spectrum analyser

Quadcopter First Successful Loiter…

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After the vibration issues were sorted out it was time to test the loiter and auto modes. A video of the first successful loiter test can be seen below. The APM 1.0 seems to hold its position reasonably well given that there was a slight breeze that day. The quad-copter was also instructed to land in loiter mode. The video was taken behind our engineering building at Stellenbosch University. We have also tested the auto mission, takeoff and landing successfully.

The new motor mounts were made by Johan Frank from Malmesbury on his own CNC machine with simple number-plate plastic. These new motor mounts are much less brittle and therefore much stronger than the original perspex parts.

Maiden Flight….

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After the quadcopter was fully assembled including ESC’s, accelerometers and radio calibrated it was ready for its maiden flight. This flight was carried out at the back of our Engineering building, Stellenbosch, on an insufficient piece of grass. A short video from the flight can be watched below.

After some time flying the altitude hold function was tested which seemed to work. However, when testing the second time and switching it off, the throttle was in a lower than hover position, causing the quad to come down hard. This caused three perspex motor mounts to be snapped off. Luckily this exposed some weaknesses in the frame. The motor mounts will now be manufactured from a slightly less brittle plastic. Ignoring human error (first ever flight) the quadcopter flew excellent the first time.