ARDUINO+LCD SURGE PROBLEMS OR EMI(Confused)

hi friends;
I am using arduinomega 2560 to control a ac heater. Using an arduino pin to give pwm to a solid state relay which has the heater connected to its o/p(350W is heater wattage). And I have a LCD JHD204A connected to read the temperature reading. I am using a SMPS to power the arduino and subsequent pcb. And the heater and smps both get ac supply from mu household socket. The problem is whenever I switch on and off my other devices in household like fans, lights etc. the LCD display gives a distorted view what can be the error.

This sounds like EMI from the other devices.
The real cure is to suppress the other devices although putting extra / more effective supply decoupling on the LCD could help as well.

hey hii...can you tell me what value capacitor i should use and what type of capacitor the ceramic one or electrolytic one.....thanks in advance

Always use a 0.1uF ceramic capacitor, this is for the high frequencies. Then you can add a larger electrolytic one in parallel for the lower frequencies. Start with 47uF but you might have to go up to 1000uF or bigger depending on how much disturbance you are getting.

I had also suffer from this problem.It is very common when you are controlling AC loads using relays.My fix is to put a polyester cap in parallel to the relay. Also try to create a magnetic shield isolation in the LCD lines like a aluminium foil connected to ground.Just connect to one side to prevent ground loops.Alternatively give preference to cables with a shield protection.A CAT6 UTP cable has that shield for example

Also try to create a magnetic shield isolation in the LCD lines like a aluminium foil connected to ground

While aluminum foil can shield from induced electric fields it is not a shield against magnetic fields. For that you need mu-metal.

Using an arduino pin to give pwm to a solid state relay which has the heater connected to its o/p(350W is heater wattage).

PWM for AC heater..........
Or did you just mean its a ON/OFF switch with the pin output HIGH/LOW?
Heaters are electrically equivalent to small inductive coils with high current.

This is just a guess cause I don't know the wiring but if you are using PWM and this interference on the LCD only happens when the heater is on, then your wiring is causing it.

PWM is 3-60KHz, and if that is switching a 60Hz line, while controlling a high current, high voltage coil, there is going to be a lot of feedback spiking and dipping onto the AC line. Its hard to believe that any amount of switching on a heater with so little inductance could cause EMI directly (via air). More likely in my opinion is it these spikes and dips have no circuit to make until you turn on a light or fan, most other devices would have filters and small loads.

I have no idea what heater you are using, or if what I just said is whats going on. Using a cap will probably fix it, but thats kind of a band aid solution. If there is really enough EMI on a AC line or the air to mess with a LCD screen being powered from a DC supply, you have other things to worry about. All that interference will strain other devices and if there are high current spiking happening its not good for the wiring.

HugoPT:
My fix is to put a polyester cap in parallel to the relay.

The problem with that, is that you now have a huge surge current when you try to turn the relay on, which is of equal or greater magnitude to that on switch-off.

Note that a "snubber" diode very effectively limits the kickback voltage from the relay, but the current (inductive) transient appears in the circuit loop comprising the diode, the switch transistor, and the power supply, so the diode needs to be located adjacent to the transistor and not at the relay, and you need your decoupling capacitor here as well. Driver ICs containing the snubber diodes are well designed in this respect.