LCD IC2 20x04 Dont show caracters after some cycles 220V control

Other Hardware Displays
1

Resume;

And LCD 20x04, is stoping to be outputing text, and only sow symbols and random stuff. Its is used to control a 220V industrilal refrigeration room.

-Yes it has snubbers
-Yes it has 2 2.2K resistor to keep the SDA and SCL at high

The set up;
-Arduino Mega
-8 Relay Strip
-Lcd Display 20x04 and IC2 adapter
-Buck converter.
-Capacitor filter to smooth voltage of the buck converter.
aaa]aaa

Outside

The thing itself starts and works properly, the code dont frezee. But once I was watching, the lcd display become full os random simbols when the system stop... It meas the relays was open and since I dont have a scope I can only assume the High voltage peaks damage the data trasmiton.

After some research, a post of Nick Gammon strongly suggest the use of 2.2K resistor to keep the SDA and the SCL at high mode, I install one of these... buth the problem persist.

interior

So I make some snubbers out of 400pF and 8W 300ohm resistors and put in parallel with the main contacts of the 3 mayor inductive loads...

snubbers

2 evaporator fans (5 small fans) rating 2.5A
1 Relay coil (the contactor of the compressor unit)

And the screen was legible for much much longer, it dont clear at start or stop. The thing is ... it clears or it become full of garbage at some point during the day.

Board interior

So, I will add another snubber for the other major inductive load, a solenoid coil, yet, I dont know whath is more recomendably for it a snubber or a variac?

Thanks for your tougths on this so far.

I was reading I migth be necessary a capacitor in the pin 1 and 2 of the LCD.... "First try - a 47 µF capacitor connected between pins 1 and 2 on the LCD." on another topic.

Main Questions is... The solenoid coil must be in parallel with a snubber or with a varistor ?

Thanks in advance.

-Alex.

2

Well... I was there a while a go, and when the compressor stops... the screen turns clear and dont comeback... so... the only thing dint have a snubber is making a high voltage peak... I will try to put the snubber in its place, and see what happens.

3

Try a 47 µF capacitor directly across pins 1 and 2 of the LCD.

4

this is a medium cap...
I will try... but whats for?

5

Well... today I make two more snubbers

Capacitor 0.01uF
Reistance 1/2Watt 1K

Its seems the problem is gone.

Never the least, I will wait at least 3 or 4 days to call this solved.

Thanks.

6

Can you post your relay strip schematic?

7

Well... I dont make the relay strip; i just buy one, I will post some photos of it latter on.

Or if you mean the relay and snubber diagram, that can be arranged.

-Alex.

8

AlexLPD:
Well... I dont make the relay strip; i just buy one, I will post some photos of it latter on.

Or if you mean the relay and snubber diagram, that can be arranged.

-Alex.

never mind I just realized this is duplicate thread. I still believe the problem is in the REMF protective diode in parallel to relay coil not shorting to ground, but just shorting the coil only. The snubber across the relay contacts probably does very little to protect 5V supply. It also does not explain why only the LCD is affected, problem with power should affect processor, AKA it MAY reset, but it does not.

9

Vaclav:
never mind I just realized this is duplicate thread. I still believe the problem is in the REMF protective diode in parallel to relay coil not shorting to ground, but just shorting the coil only. The snubber across the relay contacts probably does very little to protect 5V supply. It also does not explain why only the LCD is affected, problem with power should affect processor, AKA it MAY reset, but it does not.

Yes, I search and seems to be a recurrent one.

Yes is a very strange problem, and right now is a very annoying one.

So, what other options to correct this can be accomplished?

Thanks.
-Alex.

10

Paul__B:
Try a 47 µF capacitor directly across pins 1 and 2 of the LCD.

I have read the datasheet
pin 1 and 2 of lcd are VCC and gnd.... is probably to have voltage splikes in the conductor to the feed of LCD?

Thanks.
-Alex.

11

The problem must be center in the hardware the software as an clear.lcd() each time the temperature changues.

In deed the clear screen seems to be taken more time between problems.

_Alex

12

Interesting there this post;

When a random numbers was occurring while there was no potentiometer to the contrast. ...
But Im using IC2 Backpack, there is a pot in there... I will trick a litte bit to see what happens.

13

well i add the capacitor across the pins 1 and 2 of the screen... the problem continues to come, at random times...
I dont Know whath else to do... there is a post when they talk about a transitor shield for calling someway
but there is not a diagram... they talk about a transistor and a capacitor... but not diagrams... any one?

Thanks.