Is 1/10000sec (100µS) so we get our result in just 100µS. We deduce the frequency by multiplying theĬounts between the leading edges by 62.5.Īn advantage of this method is the quick calculation. By using no prescaler the timer countsĮvery clock cycle (62.5nS at 16 MHz). Timer 3 is a high-precision 16-bit timer. * Frequency counter using Timer 3 to work out the interval (i.e wavelength)īy counting between two consecutive rising interrupts (leading edge) on pin D18 (int3).īased on Nick Gammon's similar program for Atmel 328P processor, here:Īdapted for MEGA2560 by Chris Jennings. If anyone is interested, here is the code: #define CJ_ID "Wavelength2560 version:C" So my listing of the numbering mismatch above seems to be correct. Since posting I adapted my code to use timer/counter 3, interrupt 3 and Attach/DetachInterrupt 5, and it works perfectly on my MEGA2560. I have yet to try using Attachinterrupt(5.) and timer/counter 3, but will do so if my understanding above proves correct Interestingly when I convert Nick Gammons example from interrupt 0 to interrupt 5 with the signal on D18 it does read the frequency correct, but only on the first reading. This suggests that if I use AttachInterrupt(5,isr,rising) with the signal coming into D18 I am actually using MEGA interrupt 3 and Timer/Counter 3 !Ĭhecking the MEGA2560 pin mapping further suggests the true mapping is: So I decided to use int.5 on pin D18 but then I noticed that maps to pin 46 on the MEGA2560 chip ("PD3/TXD1/INT3") But in trying to convert it to run on a MEGA 2560 I came across what appears to me to be an Interrupt numbering mismatch between those used in the Arduino AttachInterrupt / DetachInterrupt commands and the ATMEL numbering for the MEGA 2560.Īccording to the Arduino reference the Mega2560 mapping is: I tested on my UNO first and it worked just fine. This is the example that works by counting the interval between rising edges. I used the interrupt pins for reading changes in 8 rotary encoders, which is why I set them up as pairs.I am working with "Another Frequency Counter" program in Nick Gammon's excellent notes on Timers and Counters ( Gammon Forum : Electronics : Microprocessors : Timers and counters). PCINT-registriesĪtmega 1280 – the IC running on Arduino Mega – provides a way to run a total of 24 interrupt pins by using PCINT0-PCINT23 -pins. I need those 7 available I/O expanders for other purposes, namely for running 16 leds each.Īs usual, everything here is provided freely as is, with no warranties and in hopes it may be useful for someone. Hi all, I see into the Arduino Mega2560 specification that the Interrupts INT0, INT1, INT2 and INT3 have a line over the name (like a negative sign), the same indication is not present for the INT4 and INT5. ![]() It seemed needlessly complicated to use interrupts via the IO expander.const byte interruptPin 2 A push button is attached on the interrupt pin 2. ![]() const byte ledPin 13 Led is attach on the board of input pin 13. Use attachInterrupt() function to configure the Interrupt for rising edge, falling edge or level change on the pin. Interrupts Pins INT0, INT1, INT5, INT4, INT3 and INT2 respectively. Tutorial on Arduino Mega Pinout, Technical Specifications, Features, Layout. Below the example code of LED blinking in which the interrupt function is used to understand more clearly. A beginners guide to Arduino Mega 2560 Board. Previously I entertained the idea of using MCP23017 I/O expander for interrupt port expander, but I gave up on that avenue because: Example code of how to use Arduino interrupts. ![]() Along with the interrupts I also tackled the Serial communication issue, in order to use the end result circuit some day as a game controller for a desktop game, but that is a topic for another blog post. This weekend I finally completed my several months long venture into the Atmega interrupt registry, in attempts to get more than just Arduino Megas’ 3 interrupt pins available for my project (which calls for at least 16 interrupt pins).
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