Subscribe to RSS
The device was constructed on single-side PCB that features 3 general purpose buttons and various extension connectors. Furthermore, it can export both the wave shape and its spectrum in a file on the SD card. This was first prototyped about one and a half years ago.
I was happy with the ADC sampling rate and resolution but I was using it in its original breadboard setup as I kept postponing a proper build of this rather inexpensive oscilloscope. Also on the front side, I placed three buttons and four other header connectors. On the flip side, the board hosts two voltage regulators, satisfying the 3. There are eight vias on the top layer that I could not avoid. They don't look too nice but serve the purpose. There's a reset button on the top-right corner for obvious reasons.
The blue-pill board is covered by the TFT and so the builtin reset button is inaccessible. Also, to avoid handling the boot jumpers directly, I have created an extension three-wire cable with a three pin header at one end and a switch at the other. For further details on PCB creation, do check-out my previous article. I moved from periodically probed button status to interrupt based button press detection. As a consequence I encountered what it's known as the button bounce phenomenon which manifests by apparent quick button press events before, after or before and after the actual button press.
That is caused by an imperfect contact in the switch during on-off transitions and by the quick-to-detect MCU - the 72MHz clock frequency speaks for itself. The electronic fix for the high pulled buttons is the placing of a nF capacitor between the button signal line and GND.
In effect this filters-out the switching noise and creates a smooth passage between high and low states.
STM32F4 FFT example
I decided to throw a polarity protection diode in the schematic. This is always a good idea when you know you'll be spending some time handling the board. The board does not include an input signal processing circuit. Instead there are a couple of female headers that break-out 2 analog inputs and one digital output.
That gives a certain flexibility to the circuit permitting the addition of extension boards on top. One such board may contain an instrumentation amplifier and a voltage divider network or a 2-axis joystick and an extra button. I knew this would be a problem but I was constrained by space and other traces and I thought that a reasonable distance between the two would suffice.
Apparently it doesn't. A fair amount of switching noise affects the input. To eliminate the problem I had to turn off the calibration signal. Anyway, in theory the analog and digital signals along with the corresponding areas below the MCU need to have dedicated power planes. Given my single-sided PCB design, I had to ignore this.I always wanted to use MCU for audio processing.What is a Fast Fourier Transform (FFT)? The Cooley-Tukey Algorithm
If you do not know what is this, read Wikipedia first: FFT has a huge number examples of usage, for my case I want to build wavetable synthesizer. We have an audio signal, which is just a set of amplitudes, which you will take from your ADC.
Samples are taken with some sampling frequency Fs. A sine wave has real values.
Subscribe to RSS
But FFT results are complex-valued. Real part stores the frequency of the sine wave. Imaginary stores info about phase. But to have spectra dependence of sine wave amplitude vs wavenumberwe need np. As we see, the first freq is zero.
The first frequency is about DC offset. Our sine wave is symmetrical from zero value. The second one is our main frequency. Also, you can notice, that the number of frequencies is only 17, but a number of samples is This is because our FFT is real-valued and the number of frequencies is limited by Nyquist frequency, which is twice less then number of samples that is how I understood this, correct me in comments if I am wrong!
Link to site Unzip it somewhere. RFFT result will be put in testOuptut array. Also, notice that you need to specify FFT size, in our case, this is All additional documentation you can find there. We use printf function.
I want to print to UART. By default, printf cannot print floats. Ok, what do we need to notice?
C has its own type for complex variables, but a lot of libraries still use own ways to represent complex results. Values are packed like this:. It happens that the first complex number real, imag is actually all real. The real FFT functions pack the frequency domain data in this fashion.
The forward transform outputs the data in this form and the inverse transform expects input data in this form. The function always performs the needed bitreversal so that the input and output data is always in normal order. The functions support lengths of [32, 64,…, ] samples. Similar results in python gives fftpack. I am not an expert in DSP and this article is based only on practical experience I got. If you have any comments or improvements to this information you are welcome.
Write to me directly on a. Also, grammar fixes are welcome also:. Part 1. Python warm-up for illustration I always wanted to use MCU for audio processing.
There is nothing to explain, we do not change anything. Now we need to modify our project directory tree structure.Does anyone help me on this? In simple words FFT is used to transform some signal from time domain to frequency domain, but with litle computation effort compared with other mathematical tools I recommend you to run simulations on your processing scheme before coding it on a MCU blindly.
I have doubt that FFT works for your purpose. FFT example is here. View all questions in Keil forum. Site Search User. Software Tools. Implementation FFT in C. Thanks details; I must get the sound and put on the LCD display and let the person enter new freqs as used.
Reply Cancel Cancel. Whathave you done so far? Up 0 Down Reply Accept answer Cancel. If you haven't already done it, spend some time studying the principles behind the FFT. More questions in this forum. All recent questions Unread questions Questions you've participated in Questions you've asked Unanswered questions Answered questions Questions with suggested answers Questions with no replies.
Not Answered. Started 16 hours ago by Anupam Mishra. CubeMXLauncher termiates with error code 3 0 stm32cubemx.Cookie Notice. Cookies and similar technologies enable us to provide you with an optimized user experience and functionality of our website.
They also help us to monitor its performance and to make our advertising and marketing relevant to you. By clicking "Accept Cookies", you give your consent to their usage. Your Privacy. Strictly Necessary Cookies. Performance Cookies. Functional Cookies. Targeting Cookies.
Cookie Settings. Privacy Preference Centre Active. Save Settings. Allow All. ST Community. Enter relevant keywords and click the Search button View This Post. Some additional work might be required to add the code to your project. Don't expect too much. A M4 might be an overkill. I only had evaluated M4 cores, using the FPU. A point FFT using float took about 2. That's quite enough for real-time audio And a M3 core would be a great improvement over the M0, since the latter misses an integer division instruction, amongst others.
You only need to avoid float on FPU-less cores.Cookie Notice. Cookies and similar technologies enable us to provide you with an optimized user experience and functionality of our website. They also help us to monitor its performance and to make our advertising and marketing relevant to you. By clicking "Accept Cookies", you give your consent to their usage. Your Privacy. Strictly Necessary Cookies.
Do you have any prior experience with the STM32? So in order to start, and to explain it as simply as i can, here are some functions that you'll need :. In one of my projects, that took about 2. Just turn up frequency resolution as much as necessary, and not as possible.
You should try to break the problem down to at least two separate parts. Fft: most fft routines are hardware independent and can be debugged easily on a PC. All is involved here is to organize the input as per the requirements of your fft routines.
Adc: this part is hardware dependent but can be easily structured so that the hardware dependence is minimized. The 2nd part is specific to your target and you can figure that out on your own. The first part is easy to solve as there are tons of code floating around, from arm, St, integer or floating, You just need to have some understanding of fft and it becomes quite easy after that.
I need to calculate FFT for specific points, and not for a whole table. Surely, a single point is just an impulse - so the FFT is known? Perhaps he is meaning something like the Goertzel algorithm, to calculate individual terms spectral 'points'? And as said, these algorithms are hardware-independant. Otherwise, any sinus generated data buffer can be used for testing? I used to calculate all frequencies, to evaluate one or more spectral components in relation to the others.
The ARM example comes with a reference input signal, however not a 'sinus' wave shaped.
RFFT in STM32 using CMSIS DSP. Part 1.
All rights reserved STMicroelectronics. Cookie Notice Cookies and similar technologies enable us to provide you with an optimized user experience and functionality of our website. Accept Cookies. Cookie Settings. Privacy Preference Centre Active.This allows you to make a FFT with a few simple steps. I recommend use my FFT library for future use.
And there are also FFT functions.
All other libraries are also included in project. Very fast about FFT. In other words, you are able to know from which sinus components is some signal created. Everything about FFT is described on Wikipedia. Example on the bottom is a simple FFT audio equlizer. It will show frequencies in your audio that you will connect to pin. Sound is sampled with To get proper frequency from signal, we need at least 2 samples from one period of highest frequency we want to detect. For our purpose, if we sample with One parameter in FFT result is resolution, how good you can detect different frequencies.
This depends on how many samples you take before you calculate FFT. In example below, I will take samples for FFT calculating, but only samples will be valid to display them. What does it say to us? I will make a table on how to interpret results from FFT output. This board has LCD on it, so it can be also a little bit graphical. Connect sound to STM32F4. Tags: cmsis cortex m4 DFT digital signal processing dsp fast fourier transform fft stm32 stm32f4 stm32fdiscovery stm32fdiscoverys tutorial.
Owner of this site. Application engineer, currently employed by STMicroelectronics. Exploring latest technologies and owner of different libraries posted on Github. View Results. SystemInit. Delay 21. Read before commenting! Before you make a new comment, make sure you agree with things listed below: - Read post to make sure if it is already posted what you are asking for, - Make sure you have the latest version of libraries used in your project, - Make a clean and grammatically correct written message, - Report as many details as possible, including what have you done so far, - Do NOT post any code here.
Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. My samples of input will ultimately be values from the internal bit ADC left aligned and converted to q15 by flipping the sign bit. I haven't touched anything except removing the useless code. Learn more. Asked 2 years, 7 months ago. Active 2 years, 7 months ago. Viewed 2k times. Florent Florent 2 2 silver badges 11 11 bronze badges. Active Oldest Votes.
Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name.
Email Required, but never shown. The Overflow Blog. Featured on Meta. Feedback on Q2 Community Roadmap. Technical site integration observational experiment live on Stack Overflow. Question Close Updates: Phase 1. Dark Mode Beta - help us root out low-contrast and un-converted bits. Related 1. Hot Network Questions.