![]() Arduino MCQ: Finding Out Program OutputsĤ.Arduino MCQ: Variable Scope and Qualifiers.Arduino MCQ: Serial and Stream Communications.This is counting from 0 to 8 inclusive, and looping with a period ofĩ interrupts.The section contains MCQs on arduino programming languages, preprocessing, compilation, uploading, pin mode setting, setup and loop functions, digital and analog input output, standard libraries, serial and stream communications, operators, control structures, looping, time functions, datatypes, mathematical functions, string manipulation, variable scope, interrupt service routine, progmem utility and sizeof() function. For example, if you measure the stopwatchĪnd find it is running 0.04% too slow, then you increase that number byĠ.04% (that would give 124977971) and the drift is gone.Įdit: In a comment, 6v6gt pointed out a fourth issue in your code, ![]() Once you measure the drift rate of your stop watch, you can tweak this You can change it to fit aĭifferent clock frequency or a different OCR0A setting. The value 124928000 I wrote above assumes the ISR is called everyġ22×1024 cycles of a 1 MHz clock. If the jitter is visible, youĬan reduce it by shortening the interrupt period. ThisĪdds a little bit of jitter, but prevents the timing errors fromĪccumulating and making the clock drift. From time to time, however, it will take nine interrupts. This will increment the seconds every eight interrupts. Nanoseconds += nanoseconds_per_interrupt One billion nanoseconds: const uint32_t nanoseconds_per_interrupt = 124928000 Nanosecond counter within the ISR, and count one second once you have (which assumes an interrupt period of exactly 1/8 s), increment a Instead of counting the interrupts until the counter reaches 8 Lastly, here is a trick you may use to calibrate your stop watch. Or let it reset itself by using the appropriate waveform generation Let it run continuously, undisturbed (and do OCR0A += 122 within the Timer is incremented after rising the interrupt flag but before you Time, and your ISR may even get delayed by another interrupt. The problem is that everything the microcontroller does takes May work in this program, but it is a very fragile approach worthĪvoiding. The third problem is that you are resetting the timer with the ISR. Take a look at the timing diagrams in theĭatasheet if you need to convince yourself of this. Timer is counting from zero to 122 inclusive, which gives a period ofġ23 timer clock cycles. The second problem, which has already been raised by 6v6g, is that your Good enough, in which case you still have the option to measure theĭrift rate and calibrate it out (see below). Times smaller (in the range of 100 ppm), and a very good stability.ĭepending on you quality requirements, 100 ppm may still not be If you insteadĪre using a crystal oscillator, then you can expect an error about ten Give you a frequency that is no worse than 0.5% off, with a typicalĮrror about 0.1%. Using an external 16 Mhz ceramic oscillator should It is also very unstable, and hugely dependent on The frequency of the internal RC oscillator is good to within aįew percent only. The first is that you are using a very low quality, uncalibrated time What is the problem? well, the problem is that I'm not getting something close to 999.424ms, I compere it with my phone's stopwatch and the attiny seems to start well, but then it gets about 2-3 slower than my phone's stopwatch #include ĭisplay.showNumberDecEx(min, dots, true, 2, 0) My theory was: since I set the Attiny85 to run at 1Mhz, I can use a presale of 1024 1000000 / 1024 = 976.5625 hz, 976.5625hz = 1.024ms, 125ms / 1.024ms = 122.07, so that I need to count to 122 to get a 125ms interrupt, then in the ISR function I can count to 8 to get around 1 second, ( 122 * 1.024 ) * 8 = 999.424ms I'm making a stopwatch using an attiny85, the idea was to use the timer interrupts to count the seconds
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