Relay switching screws the LCD

Hi,

I've connected a 6V Finder Relay to one pin 7 of my Arduino Uno board.

When the relay is switched the LCD shows strange characters.

I think maybe it is because the relay consumes too much energy, but it's only a guess. Any idea?

Thanks!

Are you using a transistor to drive the relay? Does the relay have it's own power supply? Do you have a subbing snubbing (kickback) diode across the relay coil?

So long as the relay coil is separately powered the problem will be electrical interference, presumably you are switching a mains load of significant power?

Proper screening and interference suppression measures should be used - screened cables, keep relay away from logic circuitry, add ferrite toroids to cables etc.

LarryD: Are you using a transistor to drive the relay? Does the relay have it's own power supply? Do you have a subbing snubbing (kickback) diode across the relay coil?

Hi Larry,

I am brand new in this world. I just went to the electronic shop and ask for relays suitable for an Arduino board, so the guy gave me this Finder relays. I just plugged them to the Arduino outputs.

Today I've been struggling again. Then I gave up and tried to connect an FC-28 ground moisture sensor connected to the same power supply (the 5V from the Arduino board) and the LCD goes screwed as well. This makes me think that there is wether a feedback, or a voltage fall or something that my limited knowledge is not aware of... :-).

I guess I am doing a lot of rookie mistakes.

Thank you very much!

MarkT: So long as the relay coil is separately powered the problem will be electrical interference, presumably you are switching a mains load of significant power?

Proper screening and interference suppression measures should be used - screened cables, keep relay away from logic circuitry, add ferrite toroids to cables etc.

Hi MarkT,

As I just have posted, I am connecting the coil direct to the Arduino output pin.

This is probably a youth sin...

Thanks

I guess I am doing a lot of rookie mistakes.

Well that's one way to learn, I have been known to do the same :confused: It can be quite tempting to jump right in and get the old feet wet. There are a few basic things you should follow whenever you connect hardware to your pet Arduino.

I recommend you stop and look at a few tutorials online before proceeding: https://learn.adafruit.com/category/learn-arduino

https://learn.sparkfun.com/tutorials/what-is-an-arduino

http://www.arduino.cc/en/Tutorial/HomePage

http://www.arduino.cc/en/Reference/HomePage

https://www.youtube.com/watch?v=fCxzA9_kg6s

I recommend you also go through all the examples that are installed along with your Arduino IDE. This will give you a great framework that you can build your new hobby on.

Ask for help if you run into any problems you cannot solve. Just remember to follow the forum posting guidelines.

P.S. Never connect a relay directly to a GPIO pin without first going through a driver.

EDIT: for more topics http://www.gammon.com.au/forum/index.php?bbtopic_id=123

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FYI, when I was using my cord powered electric drill (which was plugged into the same power strip as my arduino power supply) , I noticed that my LCD displayed garbage characters when I was using the drill. I didn't have any decent size electrolytics available to put on my 5V power bus for the arduino so I don't know if that would have prevented it. I suspect you would need good size electrolytics (greater than 1000uF) on both the input (Vin) and output (5V pin) of the onboard regulator plus some 0.1 uF decoupling caps on the 5V to suppress the negative spikes on the bus that cause the garbage characters on the LCD.