i am using arduino mega 2650 with tft shield and 3.2" tft touch screen, i am already done with the software/program, now my problem is the output from the board from A0-A15, the outputs are connected to a relay module which serves as my switch but the output from the arduino cannot make the relay on/off, can you help me from this problem???? thank you in advance, i am hoping for your great replies.
Very hard to say without a look at the code or schematic. Just a guess, but have you wired the arduino outputs directly to the relay? If so, it's quite possible that the arduino can't source enough current to switch them. Take a look in the playground at the example for wiring up a solenoid - it shows how to use a transistor & flyback diode to wire such things up.
Do you have a common ground point between the two boards? If not, and really only have 16 leads running to the relay inputs as you said, then that's likely going to be your problem (unless the relay source limit that wildbill mentioned is it).
Maybee you should look at getting a couple of thesehttp://www.ebay.co.uk/itm/New-5V-8-Channel-Relay-Module-Board-for-Arduino-PIC-AVR-MCU-DSP-ARM-Electronic-/170745298865?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item27c1367fb1&_uhb=1 they are only cheep and require about 16mA per port.