#01 I'm leaning towards relay EMI interfering with the microcontroller or LCD.
I dont know much but ,,, if we replace the Resistance with the Diode is it not sufficient (say IN4007 and 1nf) will it not suppress the EMI of the Relays'
Electromagnetic Interference (EMI) is not reliant on wires or copper traces to propagate, it is the typically unintentional generation of electromagnetic waves/energy which can propagate the air like Radio Frequency (RF) or Electromagnetic Pulse (EMP).
In the case of the above design probable sources of EMI are the relay contacts and the motors being controlled.
The RC network across the output of the TRIAC is essentially a snubber network designed to counter EMI produced by the TRIAC switching On/Off, as well as the load, the motor being controlled.
While the diode across the relay coil, is intend to safely channel Back EMF or Fly Back Voltage as it is commonly referred. Such Back EMF occurs when the magnetic field of a inductor, like the relay coil, suddenly collapses generating a large voltage transient.
The issues are two different and distinct problems with which must be dealt accordingly.
EMI can be received by wires, copper traces and components of the design and in turn can produce transients and noise on various signal paths with adverse effects.
Common Electromagnetic Compatibility (EMC) are bypass/decoupling capacitors, snubber circuits, shielding, proximity, solid state relays, multiple proper ground planes, ferrite beads, etc.
#02 You might try three caps in parallel something like, 1nF, 100nF and 4.7uF.
Please Explain the Theory and Practical use of it
Capacitors of differing composition and values react differently to various frequencies and characteristics of various EMI sources.
By ganging several different capacitors in parallel of different values and composition, the group can bypass/decouple a wider range of EMI.
#03 the 12V supply is driving up to six relays and their driver circuits
now do we need more then 1A of current to drive the 6 Relays??
Perhaps, it largely depends on the specifications of the relays being utilized in the design.
The important point I was attempting to convey is that without proper heatsinks linear regulators, like LM7805 and LM7812, the maximum heat dissipation drops sharply and so too does the available current.
#04 Future reference, a possible better design would have been to locate the relays, their driver circuits, BT136, MOC3021 and snubber circuit on one PCB and the microcontroller along with signal conditioning opamp circuits on another.
sir what if want to have all the Sections on in one PCB and why do we need to separate them??
As explain in response to your first question, sources of EMI, in this case the relay contacts, can be somewhat countered increasing proximity/distance from the EMI sources.
The design could be placed on a single PCB, however more thorough EMC measures maybe required, like shielding, grounded Cans over the sensitive components, etc which you can often observe in various RF and test equipment.
Another option is to utilize solid state relays in place of the mechanical relays which will alleviate much of the EMI from the relay contacts.
You can Google most of the topics for a more in depth discussion and there are numerous publications available which deal with each topic exclusively.
BigDog