Arduino Interrupts Revealed

[@IntegralMoon]

Just an addition, to my understanding; volatile also tells the c compiler that the value of a particular variable can be changed externally to the program (i.e: in an interrupt). Without declaring volatile, the value of a variable that changes only inside an interrupt will will "optimised" to a constant.

[@LewisLoflin]

What it means is the variable is stored in RAM not a register. Non-volatile will work but according to the literature it can be inaccurate.

[@Clip7heApex]

Such a mine of information in this video!

[@alleksandrs]

Thank you very much! I did not understand why a *delay()* command does not work in my timer interrupt subroutine, and spent many hours for troubleshooting until I luckily found your video and you explained it very clearly at 12:09.

[@LewisLoflin]

When you call an ISR it disables all other interrupts - delay() uses interrupts which is why I use my own delay routine.

[@martinkolar2008]

@@LewisLoflin Hi, thank you for your excellent videos! Just one note - your myDelay(int x) routine actually delays for one more millisecond than indended, since the variable i is going from zero. Should be for (int i=0; i

[@timstrack4573]

Great presentation

[@WistrelChianti]

I came here hoping to find out about interrupt registers... I came away having learnt what volatile actually does, and found out that Triacs and SCRs exist and what they are, and having learnt about phase controlled limiting of AC power output... I'm not complaining.

[@whitefields5595]

Minor slip, at 7:21 you press switch it goes from low to high (not high to low as you say). Great video, thanks

[@LewisLoflin]

The switch closure pulls the pin from high to low. This is because of the internal pullup as I remember. Wasn't clear on that thanks.

[@whitefields5595]

Lewis Loflin OK, I was wondering if you were pulling down. Useful to note that I think the 328 data sheet says pulling down is more reliable. Thanks again. (While I have your attention don’t forget to make the trailing edge phase control video ...Greatscott has done one recently, but the subject needs the LL treatment!

[@LewisLoflin]

@@whitefields5595 Thanks. One can only pull down if using internal pullups. Again this illustrated leading and trailing edge. I normally would use falling. Thanks.

[@TheOldmankk]

Thanks pal, always learnt something from your clips.

[@tubeamplifiermk2305]

How about interrupts in software. How to do an ISR when, for example, specific amount of hardware timer ticks happened? Have you tried that with atmega328p (uno/nano)?

[@evangelosbrouzoukis429]

I don't know if you read those things, but you are not just quoting the manual here, are you? Nice to meet you, Sir.

[@LewisLoflin]

I read the specs but built the circuits to see if they work. For example the manual never said NOT to use delay in the interrupt routines.

[@christheother9088]

I would probably want to try a hall effect tach setup using interrupts to count rotations.. Is there a way to detect or calculate the shortest usable duration between events? Presumably you need some minimum processing time between interrupt events and when that goes to zero you are swamped!

[@LewisLoflin]

***** The deal is while servicing an interrupt (ISR) other interrupts are ignored until a return is issued. If using say INTR0 and an interrupt comes in on INTR1 that will be serviced (if programed) afterward - but if multiple interrupts occurred on INTR1 they are lost.

[@txkflier]

My eyes glazed over at the 20 minute point..

[@takedowntheccp.5167]

hi ,can you add the chinese subtitle. I want study followed to you. thank you much.

[@adilmachrouki4173]

Hello Lewis Loflin i work for long time to understand pin change int but it doesn't work i want to have code wich use pin 7 (on arduino uno ) as pin change int to turn on and off led on pin 13

[@LewisLoflin]

+Adil Machrouki If pin 7 isn't a hardware interrupt pin it won't work unless you use what is called polling.

[@cyber2244]

#include #include #include #include include all this and use attachPCINT(digitalPinToPCINT(pin no.),function, CHANGE); only work with CHANGE.

[@makissavaidis9046]

how to read with interrupt a keyboard with network of resistors in a pin (or two? one for the int and one for the analogRead())

[@LewisLoflin]

makis savaidis Not sure what you are asking. Are you referring to a PC keyboard? There is a library for that.

[@jaakkooksa5374]

Can you debounce the buttons programmatically?

[@LewisLoflin]

+Jaakko Oksa Yes you can.

[@jaakkooksa5374]

+Lewis Loflin Thanks Lewis, I am just starting with Arduino. Ordered some Arduino cards, motors, micro switches etc. from China, waiting for them to arrive. I decided build an automated tea bag dipping machine for a first project :-)

[@LewisLoflin]

Great!

[@longdongsilver4719]

Normally your ISR should be as fast and as short as possible. So it is just absurd to put a delay in an ISR.

[@rolandberendonck3900]

As far as I know the compiler will even leave it out. But haven't tested it myself.

[@davidw7015]

OFF topic: Your UTube audio is weak and muddy on MAX volume! ........ Well it's back when I pull the headphone plug partly out. This has happened on two UTube videos tonight. Others are fine. It repeats on those same videos and makes absolutely NO SENSE! Anyone experienced this?

[@LewisLoflin]

This video has been out a while and I have better equipment than back then so I'll make an updated video on this subject.

[@davidw7015]

Lewis, don't make any updates because of my experience. When the audio came back (partly pulling the headphone jack) I could easily understand your voice. There is a bit of noise but not bad. The PC speaker works like it should! The reason I posted is this is a strange effect. It occurs at exactly the same places on those videos that display it. On one video the ad at the beginning is just fine but the following audio is bad. Although it is good on the PC speaker and a partly pulled headphone jack a fully inserted headphone has this inability to play some sections of the audio that otherwise is fine on the PC speaker. I am an engineer and want to know how this can be possible. Maybe the left and right channels are 180 deg out of phase on some audio and are cancelling each other? Just my first guess.

[@LewisLoflin]

Needs to be updated and additional material added. Thanks

[@tombudd1281]

Delaying for 5 seconds inside an ISR? Are you mad? I get this is a basic instructional video, but that would kill more sophisticated programs.

[@LewisLoflin]

This is a demo to learn what interrupts are.

[@cr6925]

You can do whatever you like in an interrupt, including a long delay IF that's how you've chosen to use your interrupt.