Actions
Forum Thread Details
  • Replies 34 replies
  • Subscribers 401 subscribers
  • Views 9693 views
  • Users 0 members are here
Related

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

  • How are you driving the relay from the arduino? Direct off the micro or via a transistor? Does the relay have a snubber cap across the coil and a back emf diode? Does the arduino have a filter capacitor near the supply rails?

    All things to look for to prevent the back emf.

     

    Also you may be getting induced noise in your supply from the triac switching, again check for supply noise with a scope perhaps?

     

    HTH

    Warren.

  • in reply to WarrenW

    Hi sir,

     

    I don't have a scope (and that's a problem, I know).

     

    The relay is a module (SRD-05VDC) and yes, it's being driven directly from the arduino.

    No filter near the supply rails. You mean a cap through vcc and gnd supply right?

     

    I'll try to get my hands on a scope in the next few days.

     

     

    Regards.

  • Can you please provide a schematic of your setup and also a full picture (Cant see all your connections in the one provided. You can upload them right into this community post.

     

    I have done what your describing on several occasions and not run into mains based issues so this is why I am interested to se how everything is wired

     

    You should not need a scope to fix this and if the LCD is connected as I think it is, then the scope will not help a lot.

    Thanks

  • in reply to Robert Peter Oakes

    Also

    If the LCD gets corrupted it really needs a power reset.

    There is no reset pin on the controller in these displays.

     

    As Peter has suggested a schematic of how you've connected the relay and more importantly how you drive the relay (turn it on/off) will help with the answer.

     

    Thanks

    Mark

  • What is your setup? It appears maybe you have some inducted noise interfering with communications from the board. Maybe you have long LCD bus lines which are more prone to picking up interference from the AC mains, which you should re-route, shorten, or maybe even use shielded cable. Perhaps try isolating the relay power supply lines from the LCD lines by having separate ground wires (in the case you've commoned them up on a breadboard in a "bus" fashion). I would also suggest increasing the separation between a phase control device and the arduino, as many of those devices have high in-rush currents when "cutting in", and this can result in significant EMF generation. Another possibility is that you might have short voltage dips when switching your phase-control dimmer (information might be necessary), so perhaps try thicker Vcc/GND leads to the display and bypassing the supply with a sizeable ceramic/MKT polyester + electrolytic capacitor at the display itself could help.

     

    - Gough

  • It sounds like your arduino is not crashing, just the display is getting corrupted data.

    You can try checking the clocking signals to the display - make sure they are low impedance connections not running close to high voltage AC wires.

    Try disconnecting the clocking signals and grounding the display clocks at the display to confirm everything else is running properly and no random characters get clocked into the display. If random characters still show up, then the power supply to the display becomes the next most likely issue - put a large capacitor across the display power supply. Try moving the AC parts of your circuit further away from the digital parts.

  • I would go so far as having the breadboard for the LCD diferent from the one for the higher voltage.

    clem

  • Hi all,

     

    Thank you all for your time.

     

    I took a picture today of the system today. It's not very "clean" but I was really short on time to test it. You can see it here: https://1drv.ms/i/s!Ah12lhUG5VG8g9FU0eNo8CpDdW1WYQ  I'll try to post the schematic later today when I arrive home.

     

    I have done some measurements with a scope with a borrowed scope. The 5V supply is getting lots of spikes when I open or close the relay (more when I close it so I only took pictures of closing).

     

    This is what I measure: https://1drv.ms/i/s!Ah12lhUG5VG8g9FRBvXyADPi7U7WZQ

     

    Then I add 2x470uF capacitores to 5V: https://1drv.ms/i/s!Ah12lhUG5VG8g9FS6mhCWvuhGU6JZw

     

    Not very helpfull. So I was reading around and added a snubber in paralel with the motor to see if it gets any better: https://1drv.ms/i/s!Ah12lhUG5VG8g9FTdvyVX-heJbancA

     

    So, basically I think the problem is the coil on the relay that is giving me all this spikes.

     

     

    I measured the system with the phase angle control and I get some noise at low firing angles but it doesn't seem to be enough for the problem... the noise is very low.

     

     

    Thank you all in advance.

  • The schematic it's this but with arduino Mega.