Relays turn on, then shows garbage in LCD

Hello everybody, ¿can somebody help me please?!!!!! Cry

I using a arduino duemilanove board, and LCD display LCM1602A (blue backlight), and a 74HC595 that drives a ULN2803A and this drives relays to 12VDC.

When I tested the relays to drive a load(with a PC power supply), I had conected the load trough a solid state relay, I mean, between the relay and the load is the SSR, under this configuration all has worked nice. now the configuration is without SSR(with 2 tiny cheap power supplies) , the weird thing is the garbage in the LCD once the relays turns on, the system continues working fine except the LCD(full of garbage!!!).

The problem is in the external electric system 110AC? cause noise for switching relay? or the internal electric system 12VDC? when the coil of the relay turns on?.

first I used 2 tiny cheap power supplies, one for 5VDC another for 12VDC then the garbage get very fast in the second or third switching.

After I used a PC power supply and the problem take more time to appear, 30 minutes or more.

I am pretty sure that is the power supply. I am using a IDE 0018 with the LCD library that comes with it.

Please help me. and Thanks for your time.

Could you sketch out your circuit? Have you got back-EMF protection diodes on the relays (I assume they're electromagnetic relays)?

It sounds like you are switching 110 VAC with the mechanical relay? That is, you said it worked with the SSR but not without it.

I don't think it's the relay coil circuit because 1> it worked with the SSR and 2> the ULN2803 includes anti-parallel diodes.

I would try an R/C snubber across the relay contacts. That is, a resistor and a capacitor in series. Perhaps .1uF and 470 ohms, off the top of my head.

oh, you gonna kill me :-[. when I had make the tests with the solid state relay, I used just a resistive load, but right now I need turn on a sparking device those for ignition of gas and it makes a lot of noise . I figured out that is the load, because it was worked fine all the night with a resistive load and without SSR. How can I suppress all that noise? that device makes a 2cm electric arc and that is pretty noisy.

Mark, the R/C snubber can block that noise?

-- the ports ...LiquidCrystal lcd(13, 12, 11, 10, 9, 8); I use the port that have a led, I have the hope this isn't a problem because works fine.

I don´t use a potentiometer, I use just a resistance for the contrast. is this a problem?

thanks for your time boys.

Wow! That's not going to be easy.

For sure, you need a snubber across the relay contacts. But I don't think that will be enough. You're going to get a lot of high-frequency into your circuit everywhere. You have to attack this both on the sending (sparker) and receiving (LCD) ends. Make sure you have small ceramic capacitor across power to LCD, right at the LCD board.

Make sure you have a good clean ground, preferrably a plane. Make sure all I/O lines from the board have small capacitors, say .001uF, to ground. Use similar capacitors between all LCD module wires and it's own ground.

You might try ferrite bead on the lines to the spark device. You could put a small capacitor across the power input to the sparker, right up next to it.

I'm having the same problem. My LCD flickers and sometimes even shows the sparkfun logo meaning it has shutoff or reset. It seems that I need to take more precaution in my setup to prevent a surge of current or voltage from the relay when it closes or opens. But I'm not sure how to go about this. Everything else works like I want it to except for this surge of current. I have re-soldered this relay circuit three times now even trying two IN4004 diodes in parallel, using other relays, etc... This project has to be solid. I want to add another relay to it to control something else but am afraid it will double the frustration...

I have an arduino Duem with a Serial LCD-09394. I have two TMP36 temperature sensors coming in on analog(0) and analog(1). I have a 5A, 12V relay and 2N4401 transistor WITH 1N4004 diode setup just like this however my relay circuit is opening and closing an 120V ASCO water valve.

My schematic is here:

My program is here: please know that I am no programmer. not even really sure how to add code to this forum, guess I'll copy it to notepad and put it on a website:

To be clear, my question is: First of all, is my relay circuit surging the arduino or LCD? If so, how can I protect them better?

BTW, I do have a solid state 25A 120V Crydom relay that inputs 3V to 32V. It has each node labeled (1) through (4), check the picture.

I couldn't get it to work though. I had a negative from arduino to the negative on relay(4), positive from digitalout on arduino to positive on relay(3), and i'm assuming (1) and (2) become closed when arudino sends a 5V to (3). but it no worky. any suggestions as I think this relay would be better.

-thanks Jay

Your problem is most likely RF energy from the relay contacts sparking when switching the valve. It can be radiated from the relay contact gap to the LCD or the board, or it can be conducted, or conducted through the valve wiring and radiated from there. Probably all of the above. Try an R/C snubber across the relay contacts. Say, .1uF in series with 100 ohms. The capacitor will see AC so must be non-polarized. A 600 volt film-type is a good choice. The resistor isn't critical as long as the switching rate is low. Make sure the solenoid wires are routed together as a pair and that they don't run near the LCD or the logic circuits.

Great I'll try the rc snubber. thanks.

Hi again,

finally I decided change the relays with optotriacs, and the sparker with a hot surface ignitor now works fine but in my design I have 2 layers PCB and ground plane in each layer(side) with the objetive of shield the circuit, searching information about PCB design I found "ground loops" could be awfull and each ground pin from every device takes ground from both planes, ¿I can´t use ground planes in the 2 sides of PCB?,

thanks for your time....

hi jay, I wondering why that SSR crydom doesn't work, the current is so low, about 7mA for 5V.

Do you test the SSR with a DC powersource??

BTW, I replaced the mechanical relays with a simple circuit that I found in the datasheet of the moc3061, uses a bt139 and include a RC snubber for inductive loads like your ASCO valve could be...check this out....