实时FFT绘图

Question

I have a bit of am odd question that I am hoping someone here can help me with.

BACKGROUND: I am trying to design a system that will take in continuous-time data from a VLF antenna/preamp system which will take that data, do an FFT analysis of on it (magnitude versus time) and plot the resulting FFT data as a real-time spectrogram. The project is what is known as a "hum sniffer" but specifically to see signal interference in the 15 - 35 kHz range. I have purchased a couple of "teach yourself java" books and am in the process of reading them. I am an engineering student with limited experience with programming in Ansi-C and Matlab.

QUESTION: There are several applications on the Android market that will perform a similar function using the microphone as the input source and I have purchased all of them just to see how they operate. I have also purchased an Arduino Uno with USB Host shield from Sparkfun as well as a IOIO board from Sparkfun. I am really REALLY hoping that I can use a combination of those boards I have purchased in conjunction with the aforementioned antenna/preamp system to plot those real-time spectrograms in an Android program I have yet to create.

I am not looking for anyone to hold my hand through this process but if anyone has any experience with anything similar I would appreciate any insight. My major concern at this point is whether I need to design the external system to do the A/D conversion before feeding that data into the phone or if I might be able to send the CT signal data into Android directly and have the phone do both the A/D conversion and the FFT plots. Oh, and whether or not I can use the USB port to send data into the phone.

I am using my Nexus S 4G for all testing/applications.

Thanks in advance for any input.

Answer 1

Have you tried connecting your audio on the phone's headset microphone connection and using a sound recording app? Then you should get a file that you can read into Matlab and play around with to get an idea of the capabilities of the audio input on the phone.

If the audio input good enough then writing an app to do real-time FFT and plotting shouldn't be too tricky. That way you avoid dealing with Arduino and the Android USB accessory support.

Answer 2

IOIO hardware is capable of 500ksps. This is currently being limited in firmware to 1ksps per channel in order to bound the USB bandwidth being used. However, it is super easy to change (a single number, and a firmware rebuild) in case you know what you're doing and won't overflow the USB channel. A single sample on a single channel will be a 3B message. At 40KHz, this would be 120KB/s, which is within the effective bandwidth that has been reached over ADB (the maximum is about 300KB/s). If you need help rebuilding the firmware, the ioio-users list is your friend.