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16*2 LCD getting weird characters

jrcs

Hi all.

 

This is my first post so I hope it is at the right place.

 

I'm working on a project whose objective is to control two ac loads (one ac fan, controlled by phase angle control and one ac motor controlled by a 5V relay) and output to an LCD the room temperature and the % of fan speed.

 

 

The code I wrote seem to work fine without the AC loads connected. I tested it for long periods of time (+12 hours) and everything is ok.

 

The problem is when I connect both (or just one) AC loads, I always end up with my LCD info corrupted like this:

 

image

 

https://1drv.ms/i/s!Ah12lhUG5VG8g9FOhR9Y0ccFTsq2Rg

 

Sometimes past 2 minutes, sometimes past 10 minutes... It's random but it always end up like this.

 

 

I'm guessing it's noise problems due to the loads switching TRIAC/Relay. The TRIAC its connected trough a optocoupler but the relay it's directly connected to the arduino.

 

 

First, I put the lcd.clear() function in my code to "rebuild" the info from time to time but it doesen't work 100% and it's not a "clean" solution for the pourpose.

 

 

The AC loads are connected to the grid but the arduino is powered from my computer's usb port. Already put an EMI filter into AC main input of my loads but no solution.

 

Is there a solution to this problem? Any help?

Sorry for my poor english but I'm a little bit rusty.

 

Regards

Parents

  • Hi

     

    I don't have any lamp available so I didn't test it with a lamp.

     

    I've been reading around and I found that adding a capacitor in the relay's output connections would help. The thing is when the relay latches and delatches creates an electric arch strong enough to mess up with the coil and the 5V supplying it!

     

    I add a 0.33uF capacitor and I get better. I didn't have any LCD problem for 20 minutes (way more time than before!) and this is what I've got on the scope with the capacitor plugged in:

     

    image

    Now, I don't know if this is an "acceptable" spike. I don't think so but I'm not and expert. It obviously isn't a perfect solution though.

     

    Another thing, when I turn on/off the system's 230V connection, I get some noise too. (Just by turn the 230V switch on). Is there any easy way to get rid of this "switch on noise"?

     

    Thanks in advance

    Regards

Reply

  • Hi

     

    I don't have any lamp available so I didn't test it with a lamp.

     

    I've been reading around and I found that adding a capacitor in the relay's output connections would help. The thing is when the relay latches and delatches creates an electric arch strong enough to mess up with the coil and the 5V supplying it!

     

    I add a 0.33uF capacitor and I get better. I didn't have any LCD problem for 20 minutes (way more time than before!) and this is what I've got on the scope with the capacitor plugged in:

     

    image

    Now, I don't know if this is an "acceptable" spike. I don't think so but I'm not and expert. It obviously isn't a perfect solution though.

     

    Another thing, when I turn on/off the system's 230V connection, I get some noise too. (Just by turn the 230V switch on). Is there any easy way to get rid of this "switch on noise"?

     

    Thanks in advance

    Regards

Children
  • in reply to jrcs

    Some fancy systems use a triac to turn on AC - where the triac circuit is designed to only turn on when the voltage is crossing zero - this minimizes turn-on noise.

    Can you use a solid state relay? It should have less spark noise.

  • in reply to dougw

    I have another system running with a MOC3041 with zero-cross detector and it runs like a charm.

     

    I haven't had LCD problems since the capacitor instalation but I get those spikes I posted in the image above. Are they dangerous to the Arduino or they are considered safe?

    I can't use a solid state relay on this project.

     

     

    Thanks for your help

    Regards.

  • in reply to jrcs

    I've seen lots of chips survive that type of spike, but it may stress them.

    Maybe a zener diode would be fast enough to clamp the spike....

  • in reply to jrcs

    Joao

    when the relay latches and delatches creates an electric arch

    You're quite correct ... this will happen and does so with capacitive and inductive loads much more than resistive loads.

    This is why relays are de-rated for inductive loads.

     

    If the 0.33 gets you past the problem, then its acceptable.

    Did you have LCD problems 20 mins later or was that how long you ran it for.?

     

    I think is right about using the MOC3041 and triac to drive it.

    This will remove all problems, and if you require a much higher current then use the triac to turn on a 230v relay coil which switches the fan.

    It will switch at zero so the noise should not be present.

     

    Mark