At the top of the serial monitor is a line in which the commands can be entered. With a pulse duty factor of 20%, 0.2 * 128 = 26 steps are used for the rise and 102 steps for the falling edge. Depending on the pulse duty factor, the sampled values are divided per period. The duty cycle can be used to create a sawtooth instead of a triangle signal. See second figure with 16 steps per period. However, the shape of the curve becomes worse and worse as the number of samples decreases. With 64 samples you get 10kHz with 32 samples 20kHz and with 16 samples 40kHz. For higher frequencies, the number of samples per period must be reduced. If we use 128 samples for a period, this results in a frequency range of 5200/128 = 40.6 Hz to 5.1 kHz. If the entire FiFo buffer is filled with exactly one period of the triangular signal and no further writing takes place, the I2S interface outputs the contents of the FiFo buffer again and again at the set sampling rate.Įxperiments have shown that the sampling rate can be between 5.2 kHz and 650 kHz. Now the trick that we use to create a triangle generator with it. A FiFo (First in, First out) buffer is used for output. Other settings for 1-channel output and 8-bit are possible, but do not work. The more significant 16 bits contain the right and the less significant the left channel. ![]() The output takes place as a stereo signal, namely the right channel on GPIO25 and the left on GPO26. An operating mode of the I2S interface enables audio data, for example from a WAV file, to be output to the two analog outputs GPIO25 and GPIO26. The built-in I2S interface was used for the triangle generator. The connection GPIO26 is released again with ledcDetachPin (26). The variable ratio contains the duty cycle in percent. 127 is the maximum number of steps with 7 bits. The function ledcWrite (1,127.0 * ratio / 100) sets the duty cycle of Timer1. The function ledcSetup (1, frequency, 7) sets the frequency for Timer1 and the resolution for the duty cycle to 7 bits. With the function ledcAttachPin (26,1) GPIO26 is defined as a signal output for timer 1. These signals are primarily intended to generate pulse width modulation, but can also be used as a square wave generator with a variable duty cycle. The ESP32 has internal timers with which square-wave signals with an adjustable duty cycle can be generated at any GPIO pin. ![]() Anyone who is interested in how this works in detail will receive the necessary information fromĪnd to control the registers from the Arduino IDE Since there is no complete library for the sine wave generator, the corresponding bits must be set in the control registers of the ESP32. A sine wave is thus composed of 64 steps. In order to achieve a nice sinusoidal shape, the step size should not be larger than 1024. To set the frequency, we calculate the step size for each of the possible prescaler settings and use the one at which the smallest frequency deviation occurs. Since the increment 65536 possibilities, but the prescaler only has eight possibilities, it is obvious to try out the prescaler. You can see that in order to approximate a desired frequency as closely as possible, one has to try out one of the two variables, step size or prescaler. For small frequencies it looks like this. The entire frequency formula is therefore frequency = 127 / prescaler * increment. This means that the lowest frequency is 127/8 = 15.9 Hz. Since this is too imprecise for low frequencies, there is a second setting option. The frequency can thus be set in 127 Hz steps. ![]() That means the frequency = 127 * step size. To set the frequency, the step size per cycle can be set. Thus the internal clock is higher than 8MHz. Tests have shown, however, that the frequency with this setting is 127 Hz. This means that for one step per cycle the frequency would have to be 8,000,000 / 65536 = 122 Hz. The internal 8MHz clock is used as the clock. A period can be divided into up to 65536 steps. The ESP32 has a built-in sine wave generator that can output its signal at the two digital to analog converter outputs (GPIO25 and GPIO26). In the second part, the function generator receives a display and operation via joystick and, of course, a housing from the 3D printer. The signal can be taken from GPIO26 of the ESP32. The output voltage is only positive between 0 and 3.3 V. The pulse duty factor can be set between 0 and 100% for rectangles and triangles. The function generator supplies sine and square wave signals with a frequency of 20Hz to 200kHz, as well as triangular signals with a frequency of 40Hz to 20kHz. ![]() Since the waveforms are generated by the built-in hardware of the ESP32, there are no interference with the program flow. In this article we want to build a function generator with an ESP32 that uses 100 percent of the hardware of the ESP32. I ran the article through Google translate:
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |