![]() To avoid this issue, the ATmega328P's timers can be set to trigger interrupts on several different triggers. But there is an issue: delay() is blocking, and to make it non-blocking, you have to check the millis()'s value in each loop. Arduino's millis(), delay(), and micros() all rely on these timers to operate. So a timer that has a prescale value of 4 will see a system clock of 8Mhz as 2MHz instead. In case you are curious, the job of the prescaler is to divide incoming clock pulses by a certain value, which slows down the counter by that factor. For example, if an MCU's clock is set to 125KHz, one of its timer is set to use that clock, and its prescaler is set to 1/1024, then each increment of its counter register is equal to about 1/122 seconds, which is derived from: The source code is located on the GitHub server.By getting the value of this counter, you can determine how much time has elapsed. | ((adcPin - 14) & 0x07) // Arduino Uno to ADC pinīitSet(ADCSRA, ADSC) // Start a conversion | bit(ADPS0) | bit(ADPS1) | bit(ADPS2) // Prescaler of 128 ![]() const byte adcPin = A0 // = 14 (pins_arduino.h) The rest of the time the microcontroller can do other tasks. Only when the condition is met, we perform an action at the end of measurement. We will write the measured value to the serial port and wait for 500 ms. ![]() We then periodically check the bit ADSC and at the moment it is not set, the analog measurement is finished. If the measurement is not active, we run the analogue measurement. In it we have set whether we are doing analogue measurement. We use the variable adc_conversion_working in the function loop. Then we set the voltage reference to AVCC and pin A0. In the function setup, we enable the analog measurement and set the clock signal prescaler to 128 (as Arduino does). The example is for pin A0 and Arduino Uno. This is a modified code for measuring the voltage. as ADCL and ADCH would be locked when it completed. cause the results of each conversion to be discarded, we have to read ADCL first doing so locks both ADCL ![]() ADSC is cleared when the conversion finishes without a delay, we seem to read from the wrong channel this also sets ADLAR (left-adjust result) set the analog reference (high two bits of ADMUX) and select the the MUX5 bit of ADCSRB selects whether we're reading from channels If (pin >= 14) pin -= 14 // allow for channel or pin numbers If (pin >= 24) pin -= 24 // allow for channel or pin numbers If (pin >= 54) pin -= 54 // allow for channel or pin numbers If (pin >= 18) pin -= 18 // allow for channel or pin numbers Therefore, it is clear that we will concentrate in our source code especially on improving this line. Until the condition is met, the program will wait. while (bit_is_set(ADCSRA, ADSC)) - This is the critical line that blocks the entire program.This is another reason to use non-blocking measurements. So, in worst conditions, the program will wait for 128 instructions until the conversion really starts. Analog measurement uses its own clock signal that is slowed down and conversion starts when the logic level changes. For measurement, the prescaler setting is used against the main frequency of the microcontroller and is normally set to 128. The start itself does not begin immediately. sbi(ADCSRA, ADSC) - Start A/D converter conversion.This calculation assures that the symbols move to index values of 0 and are then easily used in the function to select the specific pin on which the analogue measurement will be made. The definitions are in the file pins_arduino.h. if (pin >= 14) pin -= 14 - On the board, Arduino has analog pins marked with A0-A6.I will only describe essential parts of the code. This is how analogRead looks like the current version of Arduino. In this example, we will write such a program. If you need to make better use of the microcontroller's time to process other tasks, it is advisable to modify the analog measurement so that it does not block the running of the program. During that time you can not do anything else. The function analogRead is programmed to block the microcontroller during measurement.
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