Sinus Signal Generator from 18Hz to 250kHz

[HelWeb]

From this excellent work as base
https://github.com/krzychb/dac-cosine
I build a signal generator to produce sinus signals from 18Hz to 250kHz.
From 50Hz to 100kHz the difference to the wished frequency is about 1%
And it works without CPU after initialisation.

Code: [Select all] [Expand/Collapse]

1. // Function generator Sin
2. // (C) Helmut Weber
3. //
4. // Provided as is as example
5. // Free for everyone
6. //
7. // 50 Hz - 200000Hz:     frequency error ~ 1%
8. // from 17 Hz - 250000   possible
9.  
10.  
11. // based on:
12. // https://github.com/krzychb/dac-cosine
13.  
14. // clk_8m_div and frequency_step are computed to give the best result for the wished frequency
15.  
16.  
17.  
18. /* DAC Cosine Generator Example
19.    This example code is in the Public Domain (or CC0 licensed, at your option.)
20.    Unless required by applicable law or agreed to in writing, this
21.    software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
22.    CONDITIONS OF ANY KIND, either express or implied.
23. */
24. #include <stdio.h>
25. #include <string.h>
26. #include <stdlib.h>
27. #include "freertos/FreeRTOS.h"
28. #include "freertos/task.h"
29. #include "freertos/queue.h"
30.  
31. #include "soc/rtc_io_reg.h"
32. #include "soc/rtc_cntl_reg.h"
33. #include "soc/sens_reg.h"
34. #include "soc/rtc.h"
35.  
36.  
37. #include "driver/dac.h"
38.  
39. /* Declare global sine waveform parameters
40.  * so they may be then accessed and changed from debugger
41.  * over an JTAG interface
42.  */
43.  
44. // Esp32 @ 240 MHz:
45.  
46. // f=125.6*step/(div+1)            [div=0..7] [calc: (div+1)]
47.  
48. // step0:
49. // 0=15.61Hz 1=--
50.  
51. // step 1:
52. // 0 = 125.6 Hz 1 = 62.50 Hz 2 = 41.67Hz 3=31.35Hz 4=25.00Hz 5=20.92Hz 6=17.86Hz 7=15.63Hz
53.  
54. // step 2:125,6
55.  
56. // 0= 250.0 Hz 1=125Hz 2=83.68 Hz 3=62.5 Hz 4=50.1 Hz 5=41.74Hz  6=35.74 Hz  7=31.35Hz
57.  
58.  // step 10
59.  // 0 = 1.248 kHz 1 = 625.4 Hz 2 = 417.4 Hz (noisy) 3 = 31.33 Hz 4 = 250.6  5 = 208.3 Hz  6=178.9 7=156.3
60.  
61.  // step 100:
62.  // 0: 12.53 kHz  1 = 6.266 kHz 2=4.173kHz 3= 3.127 kHz 4=2.505 kHz 6=1.789 kHz 7=1.565KHz
63.  
64.  
65. // step 500:
66. // 0: 62.54 kHz (noisy) 1 = 31.33 kHz 2 = 20.86 kHz  5 = 10.5 kHz   6 =20.88 KhZ  7=
67.  
68. // step 1000:
69. // 0 = 125 kHz, 1 = 62.11 kHz, 5 = 20.73 kHz    ==>>> 10 = 42.02 kHz 100
70.  
71. // step 2000
72. // 0: 249.4 kHz(unten verzerrt)  1 = 125.8 kHz (noisy)  5 = 41.5 kHz (noisy)
73.  
74. int clk_8m_div = 1;      // RTC 8M clock divider (division is by clk_8m_div+1, i.e. 0 means 8MHz frequency)
75. int frequency_step = 7;  // Frequency step for CW generator
76. int scale = 1;           // 50% of the full scale // scale 0 == fill scale = bad signal (no longer a sine wave)
77. int offset;              // leave it default / 0 = no any offset
78. int invert = 2;          // invert MSB to get sine waveform  // 3: invert 180°
79.  
80.  
81. /*
82.  * Enable cosine waveform generator on a DAC channel
83.  */
84. void dac_cosine_enable(dac_channel_t channel)
85. {
86.     // Enable tone generator common to both channels
87.     SET_PERI_REG_MASK(SENS_SAR_DAC_CTRL1_REG, SENS_SW_TONE_EN);
88.     switch(channel) {
89.         case DAC_CHANNEL_1:
90.             // Enable / connect tone tone generator on / to this channel
91.             SET_PERI_REG_MASK(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_CW_EN1_M);
92.             // Invert MSB, otherwise part of waveform will have inverted
93.             SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV1, 2, SENS_DAC_INV1_S);
94.             break;
95.         case DAC_CHANNEL_2:
96.             SET_PERI_REG_MASK(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_CW_EN2_M);
97.             SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV2, 2, SENS_DAC_INV2_S);
98.             break;
99.         default :
100.            printf("Channel %d\n", channel);
101.     }
102. }
103.  
104.  
105. /*
106.  * Set frequency of internal CW generator common to both DAC channels
107.  *
108.  * clk_8m_div: 0b000 - 0b111
109.  * frequency_step: range 0x0001 - 0xFFFF
110.  *
111.  */
112. void dac_frequency_set(int clk_8m_div, int frequency_step)
113. {
114.     REG_SET_FIELD(RTC_CNTL_CLK_CONF_REG, RTC_CNTL_CK8M_DIV_SEL, clk_8m_div);
115.     SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL1_REG, SENS_SW_FSTEP, frequency_step, SENS_SW_FSTEP_S);
116. }
117.  
118.  
119. /*
120.  * Scale output of a DAC channel using two bit pattern:
121.  *
122.  * - 00: no scale
123.  * - 01: scale to 1/2
124.  * - 10: scale to 1/4
125.  * - 11: scale to 1/8
126.  *
127.  */
128. void dac_scale_set(dac_channel_t channel, int scale)
129. {
130.     switch(channel) {
131.         case DAC_CHANNEL_1:
132.             SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_SCALE1, scale, SENS_DAC_SCALE1_S);
133.             break;
134.         case DAC_CHANNEL_2:
135.             SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_SCALE2, scale, SENS_DAC_SCALE2_S);
136.             break;
137.         default :
138.            printf("Channel %d\n", channel);
139.     }
140. }
141.  
142.  
143. /*
144.  * Offset output of a DAC channel
145.  *
146.  * Range 0x00 - 0xFF
147.  *
148.  */
149. void dac_offset_set(dac_channel_t channel, int offset)
150. {
151.     switch(channel) {
152.         case DAC_CHANNEL_1:
153.             SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_DC1, offset, SENS_DAC_DC1_S);
154.             break;
155.         case DAC_CHANNEL_2:
156.             SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_DC2, offset, SENS_DAC_DC2_S);
157.             break;
158.         default :
159.            printf("Channel %d\n", channel);
160.     }
161. }
162.  
163.  
164. /*
165.  * Invert output pattern of a DAC channel
166.  *
167.  * - 00: does not invert any bits,
168.  * - 01: inverts all bits,
169.  * - 10: inverts MSB,
170.  * - 11: inverts all bits except for MSB
171.  *
172.  */
173. void dac_invert_set(dac_channel_t channel, int invert)
174. {
175.     switch(channel) {
176.         case DAC_CHANNEL_1:
177.             SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV1, invert, SENS_DAC_INV1_S);
178.             break;
179.         case DAC_CHANNEL_2:
180.             SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV2, invert, SENS_DAC_INV2_S);
181.             break;
182.         default :
183.            printf("Channel %d\n", channel);
184.     }
185. }
186.  
187. /*
188.  * Main task that let you test CW parameters in action
189.  *
190. */
191. void dactask(void* arg)
192. {
193. double f, f_target, delta, delta_min=9999999.0;
194. int step_target=0, divi_target=0;
195.  
196.   //From experiments:  f=125.6*step/(div+1)
197.  
198.     // this frequency is wanted:
199.     f_target=127000.0;                             // <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
200.      
201.  
202.     // check all combinations of step iand divi to get the best guess:
203.     for (int step=1;step<2000; step++) {
204.       for (int divi=0; divi<8; divi++) {
205.         f=125.6*(double)step/(double)(divi+1);
206.         delta= abs((f_target-f));
207.         if (delta  < delta_min) {delta_min=delta; step_target=step; divi_target=divi; }
208.       }
209.     }
210.    
211.     clk_8m_div=divi_target;
212.     frequency_step=step_target;
213.    
214.     printf("divi=%d step=%d\n",divi_target, step_target);
215.     while(1){
216.  
217.         // frequency setting is common to both channels
218.         dac_frequency_set(clk_8m_div, frequency_step);
219.  
220.         /* Tune parameters of channel 2 only
221.          * to see and compare changes against channel 1
222.          */
223.         dac_scale_set(DAC_CHANNEL_2, scale);
224.         dac_offset_set(DAC_CHANNEL_2, offset);
225.         dac_invert_set(DAC_CHANNEL_2, invert);
226.  
227.         float frequency = RTC_FAST_CLK_FREQ_APPROX / (1 + clk_8m_div) * (float) frequency_step / 65536;
228.         printf("THEORIE:   clk_8m_div: %d, frequency step: %d, frequency: %.0f Hz\n", clk_8m_div, frequency_step, frequency);
229.         printf("PRACTICAL: frequency: %.0f Hz\n", 125.6*(float)frequency_step /(1 + (float)clk_8m_div) );
230.        
231.         printf("DAC2 scale: %d, offset %d, invert: %d\n", scale, offset, invert);
232.         vTaskDelay(2000/portTICK_PERIOD_MS);
233.     }
234. }
235.  
236.  
237. /*
238.  * Generate a sine waveform on both DAC channels:
239.  *
240.  * DAC_CHANNEL_1 - GPIO25
241.  * DAC_CHANNEL_2 - GPIO26
242.  *
243.  * Connect scope to both GPIO25 and GPIO26
244.  * to observe the waveform changes
245.  * in response to the parameter change
246. */
247. void app_main()
248. {
249.     dac_cosine_enable(DAC_CHANNEL_1);
250.     dac_cosine_enable(DAC_CHANNEL_2);
251.  
252.     dac_output_enable(DAC_CHANNEL_1);
253.     dac_output_enable(DAC_CHANNEL_2);
254.  
255.     xTaskCreate(dactask, "dactask", 1024*3, NULL, 10, NULL);
256. }
257.  

GeSHi © Codebox Plus Extension

[TinkerBearNZ]

I'm looking at the esp32 Technical Reference Manual, section 28.5.4, and it says:

A phase-shift of 0 / 90 / 180 / 270 degrees can be added by setting register SENS_SAR_DAC_INVn[1:0].

Do you think this is just a documentation error? My experimentation with the invert values has discovered useful output with values of 2 (what's used in the demo code) and 3 (inverted), but 0 and 1 generate... odd waveforms. They look like a sign error of some sort.

SDS00001.png (13.66 KiB) Viewed 71226 times

[TinkerBearNZ]

Some interesting trade-offs using this as a waveform generator.

If you use an RTC clock divider of 1, you get lovely smooth waveforms, but you can only generate multiples of ~131.6Hz (at least on my board). Waveforms up to the 500kHz range look pretty decent.

If you use an RTC clock divider of 8, you can generate multiples of ~16.6Hz, but with 8x fewer samples, so you start seeing stepping at 100kHz.

I'm wondering if they had a use case for this, and what it was?

[joydipdns]

I am new to esp32 and am using Arduino IDE. Can anyone suggest how this code can be written in Arduino IDE?

[heinzv]

I'm using a very similar code already in Arduino Studio. It should more or less work 1:1. Main function code needs to go to setup().

I have another very important question to the experts here:
I need a sine wave which shall sweep from 400Hz to 10kHz with 1Hz steps. The cosine works almost nicely BUT I could not find a way to have smaller steps thant 15.61Hz. I have tried to use the prescaler and the frequency_step but I guess there is no smooth way to get a 1Hz stepping with the combinations right?
What a pitty that the prescaler does not support a linar way to divide it to a single Hz step-width.

[Gerdchen03]

I tried this code using copy past, but complier complains. I had to add:

void setup() {

}

void loop() {

}

Now I can compile and upload code, but I didn't get any sin wave.

[joydipdns]

Code: [Select all] [Expand/Collapse]

1. I tried this code and it worked in arduino IDE for ESP32. Note: I used it to generate 200kHz and had steps in the output wave. Do change as per your need.

GeSHi © Codebox Plus Extension

Code: Select all

// Function generator Sin
// (C) Helmut Weber
//
// Provided as is as example
// Free for everyone
//
// 50 Hz - 200000Hz:     frequency error ~ 1%
// from 17 Hz - 250000   possible
 
 
// based on:
// https://github.com/krzychb/dac-cosine
 
// clk_8m_div and frequency_step are computed to give the best result for the wished frequency
 
 
 
/* DAC Cosine Generator Example
   This example code is in the Public Domain (or CC0 licensed, at your option.)
   Unless required by applicable law or agreed to in writing, this
   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
   CONDITIONS OF ANY KIND, either express or implied.
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/queue.h"
 
#include "soc/rtc_io_reg.h"
#include "soc/rtc_cntl_reg.h"
#include "soc/sens_reg.h"
#include "soc/rtc.h"
 
 
#include "driver/dac.h"
 
/* Declare global sine waveform parameters
 * so they may be then accessed and changed from debugger
 * over an JTAG interface
 */
 
// Esp32 @ 240 MHz:
 
// f=125.6*step/(div+1)            [div=0..7] [calc: (div+1)]
 
// step0:
// 0=15.61Hz 1=--
 
// step 1:
// 0 = 125.6 Hz 1 = 62.50 Hz 2 = 41.67Hz 3=31.35Hz 4=25.00Hz 5=20.92Hz 6=17.86Hz 7=15.63Hz
 
// step 2:125,6
 
// 0= 250.0 Hz 1=125Hz 2=83.68 Hz 3=62.5 Hz 4=50.1 Hz 5=41.74Hz  6=35.74 Hz  7=31.35Hz
 
 // step 10
 // 0 = 1.248 kHz 1 = 625.4 Hz 2 = 417.4 Hz (noisy) 3 = 31.33 Hz 4 = 250.6  5 = 208.3 Hz  6=178.9 7=156.3
 
 // step 100:
 // 0: 12.53 kHz  1 = 6.266 kHz 2=4.173kHz 3= 3.127 kHz 4=2.505 kHz 6=1.789 kHz 7=1.565KHz
 
 
// step 500:
// 0: 62.54 kHz (noisy) 1 = 31.33 kHz 2 = 20.86 kHz  5 = 10.5 kHz   6 =20.88 KhZ  7=
 
// step 1000:
// 0 = 125 kHz, 1 = 62.11 kHz, 5 = 20.73 kHz    ==>>> 10 = 42.02 kHz 100
 
// step 2000
// 0: 249.4 kHz(unten verzerrt)  1 = 125.8 kHz (noisy)  5 = 41.5 kHz (noisy)
 
int clk_8m_div = 1;      // RTC 8M clock divider (division is by clk_8m_div+1, i.e. 0 means 8MHz frequency)
int frequency_step = 7;  // Frequency step for CW generator
int scale = 1;           // 50% of the full scale // scale 0 == fill scale = bad signal (no longer a sine wave)
int offset;              // leave it default / 0 = no any offset
int invert = 2;          // invert MSB to get sine waveform  // 3: invert 180°
 
 
/*
 * Enable cosine waveform generator on a DAC channel
 */
void dac_cosine_enable(dac_channel_t channel)
{
    // Enable tone generator common to both channels
    SET_PERI_REG_MASK(SENS_SAR_DAC_CTRL1_REG, SENS_SW_TONE_EN);
    switch(channel) {
        case DAC_CHANNEL_1:
            // Enable / connect tone tone generator on / to this channel
            SET_PERI_REG_MASK(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_CW_EN1_M);
            // Invert MSB, otherwise part of waveform will have inverted
            SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV1, 2, SENS_DAC_INV1_S);
            break;
        case DAC_CHANNEL_2:
            SET_PERI_REG_MASK(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_CW_EN2_M);
            SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV2, 2, SENS_DAC_INV2_S);
            break;
        default :
           printf("Channel %d\n", channel);
    }
}
 
 
/*
 * Set frequency of internal CW generator common to both DAC channels
 *
 * clk_8m_div: 0b000 - 0b111
 * frequency_step: range 0x0001 - 0xFFFF
 *
 */
void dac_frequency_set(int clk_8m_div, int frequency_step)
{
    REG_SET_FIELD(RTC_CNTL_CLK_CONF_REG, RTC_CNTL_CK8M_DIV_SEL, clk_8m_div);
    SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL1_REG, SENS_SW_FSTEP, frequency_step, SENS_SW_FSTEP_S);
}
 
 
/*
 * Scale output of a DAC channel using two bit pattern:
 *
 * - 00: no scale
 * - 01: scale to 1/2
 * - 10: scale to 1/4
 * - 11: scale to 1/8
 *
 */
void dac_scale_set(dac_channel_t channel, int scale)
{
    switch(channel) {
        case DAC_CHANNEL_1:
            SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_SCALE1, scale, SENS_DAC_SCALE1_S);
            break;
        case DAC_CHANNEL_2:
            SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_SCALE2, scale, SENS_DAC_SCALE2_S);
            break;
        default :
           printf("Channel %d\n", channel);
    }
}
 
 
/*
 * Offset output of a DAC channel
 *
 * Range 0x00 - 0xFF
 *
 */
void dac_offset_set(dac_channel_t channel, int offset)
{
    switch(channel) {
        case DAC_CHANNEL_1:
            SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_DC1, offset, SENS_DAC_DC1_S);
            break;
        case DAC_CHANNEL_2:
            SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_DC2, offset, SENS_DAC_DC2_S);
            break;
        default :
           printf("Channel %d\n", channel);
    }
}
 
 
/*
 * Invert output pattern of a DAC channel
 *
 * - 00: does not invert any bits,
 * - 01: inverts all bits,
 * - 10: inverts MSB,
 * - 11: inverts all bits except for MSB
 *
 */
void dac_invert_set(dac_channel_t channel, int invert)
{
    switch(channel) {
        case DAC_CHANNEL_1:
            SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV1, invert, SENS_DAC_INV1_S);
            break;
        case DAC_CHANNEL_2:
            SET_PERI_REG_BITS(SENS_SAR_DAC_CTRL2_REG, SENS_DAC_INV2, invert, SENS_DAC_INV2_S);
            break;
        default :
           printf("Channel %d\n", channel);
    }
}
 
/*
 * Main task that let you test CW parameters in action
 *
*/
void dactask(void* arg)
{
double f, f_target, delta, delta_min=9999999.0;
int step_target=0, divi_target=0;
 
  //From experiments:  f=125.6*step/(div+1)
 
    // this frequency is wanted:
    f_target=200000.0;                             // <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
     
 
    // check all combinations of step iand divi to get the best guess:
    for (int step=1;step<2000; step++) {
      for (int divi=0; divi<8; divi++) {
        f=125.6*(double)step/(double)(divi+1);
        delta= abs((f_target-f));
        if (delta  < delta_min) {delta_min=delta; step_target=step; divi_target=divi; }
      }
    }
   
    clk_8m_div=divi_target;
    frequency_step=step_target;
   
    printf("divi=%d step=%d\n",divi_target, step_target);
    while(1){
 
        // frequency setting is common to both channels
        dac_frequency_set(clk_8m_div, frequency_step);
 
        /* Tune parameters of channel 2 only
         * to see and compare changes against channel 1
         */
        dac_scale_set(DAC_CHANNEL_2, scale);
        dac_offset_set(DAC_CHANNEL_2, offset);
        dac_invert_set(DAC_CHANNEL_2, invert);
 
        float frequency = RTC_FAST_CLK_FREQ_APPROX / (1 + clk_8m_div) * (float) frequency_step / 65536;
        printf("THEORIE:   clk_8m_div: %d, frequency step: %d, frequency: %.0f Hz\n", clk_8m_div, frequency_step, frequency);
        printf("PRACTICAL: frequency: %.0f Hz\n", 125.6*(float)frequency_step /(1 + (float)clk_8m_div) );
       
        printf("DAC2 scale: %d, offset %d, invert: %d\n", scale, offset, invert);
        vTaskDelay(2000/portTICK_PERIOD_MS);
    }
}

void setup()
{
    dac_cosine_enable(DAC_CHANNEL_1);
    dac_cosine_enable(DAC_CHANNEL_2);
 
    dac_output_enable(DAC_CHANNEL_1);
    dac_output_enable(DAC_CHANNEL_2);
 
    xTaskCreate(dactask, "dactask", 1024*3, NULL, 10, NULL);
}

void loop()
{}

[rin67630]

You want to get a blazing fast sinus & cosinus generation without a lot of code?

Try that:
void setup() {
int X=0;
int Y=1000;
}

void loop() {
y1 = y1 - x1 / 16;
x1 = x1 + y1 / 16;
}

Unbelievable, but it generates a very nice and blazing fast sinus and cosinus on x and y!

Enjoy!

[Gerdchen03]

Thanks joydipdns, it works!!
I have to generate a broken sound that is beeping. Is there any possibility to set the wave for 300ms and have a delay of 100ms?

[MickPF]

Hello,

Although I have been programming with ESP-IDF as a hobby for years, I have not yet dealt with the ESP32 registers at all.
In the context of this code, I don't understand why it is not possible to set the amplitude by calling "dac_output_voltage".

I modified this code for my purposes, but I can't change the signal amplitude.

Can someone please give me an explanation?

Thanks in advance,
Michael