Analog to digital converter arduino
Here we choose the UP_RC mode(automatic trigger on RC compare), which resets CV to zero when the value of RC is reached. The CV register can be compared with the values stored in these registers to trigger different events, according to the threshold trigger principle. There are also 3 32-bit registers named RA, RB and RC. For our choice of clock, there is a clock tick every 1/42 microsecond. The actual counter of a channel consists of a 32-bit register called CV (Counter Value), which is incremented by one at each clock tick. This last mode is used to generate a signal to trigger the ADC ( capture mode is used to make time or frequency measurements). The stopwatch can run in catpure mode or in waveform mode.
Knowing that the number of clock ticks for a sampling period is coded on 32 bits, a clock frequency of 42 MHz will make it possible to go down to one hundredth of a Hertz. The other possible choices are TC_CMR_TCCLKS_TIMER_CLOCK2 (division by 8), TC_CMR_TCCLKS_TIMER_CLOCK3 (division by 32) and TC_CMR_TCCLKS_TIMER_CLOCK4 (division by 128). Uint8_t clock = TC_CMR_TCCLKS_TIMER_CLOCK1 // clock 84MHz / 2 = 42 MHzįor this choice, the frequency is half that of the main clock, ie 84/2 = 42 MHz. To configure the ADC, we start by activating the clock for this device, by calling the following function, defined in hardware / arduino / sam / system / libsam / source / pmc.c (Power management controler): On the other hand, the maximum sampling frequency will be lower. This method will allow you to perform operations on the samples (such as filtering). We will use another method, consisting in triggering the conversions with a stopwatch (Timer), and in calling an interrupt function which will be responsible for storing the result of the conversion in a buffer. To obtain the maximum sample rate (1 MHz), the ADC must be operated with direct memory access (DMA). We will therefore use the Atmel API, and direct access to the registers for certain operations. The analogRead function is much too slow to perform digitizations sampled at several kHz.
#ANALOG TO DIGITAL CONVERTER ARDUINO CODE#
The functions of the API Atmel, whose source code is in hardware / Arduino / Sat / system / libsam / source / adc.c.The analogRead function of the Arduino API.To program the ADC, three programming levels can be used: If exceeded, the amplifier saturates at 0 or 3.3 V, which provides protection for inputs A0 and A1 (which are directly connected to the microcontroller). The voltages applied to the inputs must be between -1.65 V and 1.65 V , which is roughly the maximum amplitude of a signal from the audio output of a computer. It must be able to operate in rail to rail (full scale output) we have chosen the TL2372 dual amplifier for this. The amplifier is supplied directly from the 3.3 V terminal of the arduino.
The potentiometer is used to adjust the offset so that a zero voltage becomes 1.65 V on inputs A0 and A1 of the arduino (which will give the median value 2048 after conversion). Inputs IN0 and IN1 are connected to a unity gain inverting amplifier. Here is an analog circuit allowing to make the conversion, which we will call shifter circuit : In practice, we often have to digitize alternating signals (for example an audio signal). More precisely, the converter operates with a reference voltage VREF (very close to 3.3 V ) and a voltage equal to VREF gives the number 4096. When the gain of the input amplifier is equal to 1, this voltage range gives numbers between. The voltages applied to these inputs must be between 0 and 3.3 V. A multiplexer allows the use of up to 12 analog inputs (terminals A0 to A11). The sampling frequency can in principle reach 1 MHz. The SAM3X8E microcontroller features a 12-bit analog-to-digital converter (ADC). The arduino code presented can be used as a basis for an on-board application dealing with audio signals. The samples will be transmitted in a continuous stream to the computer, in order to be plotted in a graphics window or to undergo various treatments. The sampling will be done by interrupts triggered by a stopwatch.
#ANALOG TO DIGITAL CONVERTER ARDUINO HOW TO#
This page shows how to operate the analog-to-digital converter of the Arduino Due, in order to perform sampled acquisitions. Analog-to-digital conversion and acquisition (Arduino DUE + Python)Ĭopied and translated from original published by Frédéric Legrand ( archived copy).