ATtiny13 – disco lights using DFT

6 thoughts on “ATtiny13 – disco lights using DFT”

1. Hi, great little project!
   it’s working for me. I did the upload using Arduino IDE.
   I am using an arduino nano to program attiny with Arduino IDE software.

   Board: DiY ATtiny13 (in my case, does work only by choosing this board; otherwise, there is an DFP error)
   Programmer: Arduino as ISP

   If you have no 100k trim resistor, just use something below 100k. I am using 68k.

   thanks a lot!

2. Hi,

   please provide hex code and how should fuse settings be

3. Yes, should be fine. I’ve edited this page few days ago and I forgot to change function definition. Sorry for that. Now is up to date.

4. I use MkCLIPSE
   logs:
   main.c:45:13: warning: implicit declaration of function ‘dft’ [-Wimplicit-function-declaration]
   dft(); // do some DSP
   ^
   main.c: At top level:
   main.c:87:1: warning: conflicting types for ‘dft’
   dft(void)
   ^
   main.c:45:13: note: previous implicit declaration of ‘dft’ was here
   dft(); // do some DSP
   ^
   main.c:26:13: warning: ‘fft’ declared ‘static’ but never defined [-Wunused-function]
   static void fft(void);

   I fixed the code, but I’m not sure it’s okay (now I can compile)

   #include
   #include

   #define LED_LOW PB0
   #define LED_MID PB1
   #define LED_HIGH PB2

   #define LOW_THRESHOLD (48000UL)
   #define MID_THRESHOLD (128)
   #define HIGH_THRESHOLD (64)

   #define N (7) // N-points (FFT)
   #define B (3 * N / 4) // b-value (FFT)

   const int8_t W[N] = {10, 6, -2, -9, -9, -2, 6}; // twiddle factors (FFT)
   int8_t samples[N]; // raw samples (ADC)
   uint16_t power[N>>1]; // power spectrum (FFT)
   volatile uint8_t counter = 0;

   ISR(ADC_vect)
   {

   if (counter < N) {
   samples[counter++] = ADCH – 128; // read raw sample
   ADCSRA |= _BV(ADSC); // trigger next signal acquisition
   }
   }

   static void
   dft(void)
   {
   uint8_t a, b, i, j;
   int16_t re[N];
   int16_t im[N];

   for (i = 0; i < N; ++i) {
   re[i] = 0;
   im[i] = 0;
   }

   for (i = 0; i >1); ++i) {
   a = 0;
   b = B;
   for (j = 0; j > 4;
   }
   }

   int
   main(void)
   {

   /* setup */
   DDRB |= _BV(LED_LOW)|_BV(LED_MID)|_BV(LED_HIGH); // set LED pins as OUTPUT
   ADCSRA |= _BV(ADPS2)|_BV(ADPS0); // set ADC division factor to 256
   ADCSRA |= _BV(ADEN)|_BV(ADIE); // enable ADC interrupt
   ADMUX = _BV(MUX1); // set ADC4 (PB4) as audio input
   ADMUX |= _BV(ADLAR); // left adjust of ADC result
   sei(); // enable global interrupts

   ADCSRA |= _BV(ADSC); // start first signal acquisition

   /* loop */
   while (1) {
   if (counter == N) {
   dft(); // do some DSP

   /* LOW freqency band */
   if (power[0] > LOW_THRESHOLD) {
   PORTB |= _BV(LED_LOW);
   } else {
   PORTB &= ~_BV(LED_LOW);
   }

   /* MID freqency band */
   if (power[1] > MID_THRESHOLD) {
   PORTB |= _BV(LED_MID);
   } else {
   PORTB &= ~_BV(LED_MID);
   }

   /* HIGH frequency band */
   if (power[2] > HIGH_THRESHOLD) {
   PORTB |= _BV(LED_HIGH);
   } else {
   PORTB &= ~_BV(LED_HIGH);
   }

   counter = 0; // reset samples counter
   ADCSRA |= _BV(ADSC); // trigger next signal acqusistion
   }
   }
   }

5. Hi
   I have a code problem, my compiler shows a bug in “dft(); // do some DSP ”
   How can I solve this?

   • Hi Jacek,
     could provide some logs describing this error?

     Btw. in a december edition an EP (Elektronika Praktyczna) will publish my article about optimized DFT for microcontrollers. If it’s something you would like to dive deeper then I recommend to read it.
     /L