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False triggering interrupts in Arduino Mega2560

shwetankv007

Hello everyone,

Greetings of the day, i have been working with embedded systems for quite a while now, currently i am working on a project that dispenses water depending upon the balance from rfid card, however the system has start stop and recharge buttons connected to interrupts of microcontroller Atmega2560 with internal pull-ups driven from falling edge. The system works fine mostly however in some cases false interrupts are detected that causes functions to be activated for respective buttons i.e. start stop or recharge. I tried adding a coupling capacitor and a schmitt trigger circuit to stabilize the input but it still detects the false signals of noise.

 

Moreover a small touch on the interrupt terminals(buttons not connected ) also causes the interrupt to be triggered, any suggestions are appreciated.

 

I am using arduino for declaring and defining the interrupt pins and their respective routines. The function just hosts a flag which is then checked in the main loop.

 

Thank you in advance.

 

EDIT:-

As suggested I tried:-

1. Adding an external pullup of values ranging from 1.5k-10k but the issue persists

2. Adding the decoupling capacitor

3. Power supply is fixed and using a bench supply of 24volt stepped down by a MORNSUN buck converter.

4. Not tried the debouncing test since the problem is not related to button press. Even if the button is not pressed, if I touch the open end of wire connecting the interrupt terminal then also it triggers the interrupt.

5. the pin is not routed near a power rail or a high frequency coil/trace.

 

interrupt problem  interrupt arduino avr product design

 

Message was edited by: shwetank vishnu

  • in reply to shwetankv007

    If you are getting interrupt triggers then you have noise in your power system.

    Either switch to batteries or put some big capacitors on your power input.

    If you have access to an oscilloscope look at the power and then look on the switch input lines.

    If the power is clean, but you have noise on the input lines, put in pull down resistor to ground and use the switch to pull the inputs up to vcc.

    If you still have problems, then you must have an issue on the board itself.

     

    DAB

  • I have once used the button at ~30m with dspic33 and I always had problem in measuring signals when power supply (I mean 24V) was not properly grounded (earthed). And always use twisted pair with shielding.

    Another possible solution is add a simple low pass filter at mcu input (Best, low cost and easy solution) because in long wires you can easily get few V p2p noise which can be sufficient to trigger false interrupt.

  • As the comments suggest, there are lots of ways that noise can be introduced and trigger an interrupt.

    It can be tough to track down exactly what is happening when the issue is intermittent, but while you are working through all the possibilities, you can also try various fixes, as you have been doing with pullups and capacitors. Another fix is glitch removal. In the interrupt handler, poll the interrupt pin for 20 ms to ensure it is a valid interrupt before accepting it. If it is not valid after 20 ms, simply return without taking any action. This also works as a debounce technique.

  • So, if your system is set up within an Interrupt on a falling edge you need to then think about what is causing a voltage drop that fits the following criteria:

    the Arduino (ATmega) will report LOW if, (a) a voltage less than 1.5V is present at the pin (5V boards) or (b) a voltage less than 1.0V (Approx) is present at the pin (3.3V boards).

     

    Sounds like something is floating and sometimes if you are seeing voltage drop somewhere that is unexplained then it might mean you have a strong current draw somewhere from some peripheral (e.g. does this happen when dispensing water) and your 5V power system is too underrated to supply the current and hence you get a voltage drop.

  • in reply to dougw

    Hi Douglas

     

    I'm fairly new to arduino and I'm having the same issue. I'm getting phantom button presses due to noise on my inputs, I'm using internal pull up so cant switch to an external pull down as mentioned earlier in this post. I have around 100 buttons at various cable lengths, they all work but some are getting noise and running functions without me pressing them. I have ensured its not my power supply by running the system from a usb battery pack for a while, the issue still occurs.

     

    I'd like to use your idea of polling the interrupt for 20ms, but I'm not sure where to start. I had a look online and haven't seen other people talking about it. Everyone discusses debounce, but thats not going to help me with noise.

     

    How would I go about adding this into my sketch?

     

    Thanks

  • in reply to slocombem

    Hi Matthew

     

    There is a very clever way of doing it illustrated in this code although it is not Arduino (but could be implemented with Arduino):  AIS Alarm - Debouncing Momentary Button Switches.  Look for the links provided to Hackaday and Jack Ganssle for a complete description of how it works.

     

    If you want to simplify it further then set  a flag inside the interrupt when it occurs and then outside check if the button continues to be pushed for 20 ms or so.  Bouncing and power glitches seldom last this long.

  • in reply to fmilburn

    Stronger pull-ups than the internal ones could help too for noise (not for bounce though).

  • in reply to Jan Cumps

    I have added I/O headers to the end of the cables and they are connected directly to the arduinos. I have 6 arduino's each with between 20-30 buttons plus other sensors. When I said 100 in my past comment I was just suggesting "alot".

     

    Is there anyway of using 1 external pull up resister for the 30 inputs per board. When I looked at this I thought  each switch would need its own resistor, given the number of switches I have I decided against it. I'd rather do it with software.

     

    I am thinking about trying a 20ms delay on a IF after a button press, then checking if the button is still pressed.

  • in reply to slocombem

    Resistor network/array are very good alternate of attaching individual resistor with each button. Installing 2 or 3 resistor network is way easier than writing and debugging the code for each individual button. And these are available in both smd and pth packages. Another useful alternate of individual capacitors is capacitor array.

     

    https://www.newark.com/w/c/passive-components/resistors-fixed-value/fixed-network-resistors

    https://www.newark.com/c/passive-components/capacitors/capacitor-arrays