Relay 5v for arduino

Hello guys,

I am new in Arduino world.I recently bought and arduino mega 2560 R3 and also a 5V relay from ebay(SainSmart 5v 2 Channel Relay Module With Optocoupler for Pic AVR DSP Arm Arduino for sale online | eBay). I am checking how to connect the relay and everywhere they mention that i have to use a transistor.Is that true? I want to control 220VAC lights.Or the transistor is used when you dont have the ready made relay module.

Thanks in advance

Is that true?

Yes.

This page is about motors but the relay bit is the same for anything you want to switch from it.
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html

hi,Grumpy_Mike is a transistor necessary? cant he just connect the GND and VCC input from the relay to an external power, and the in1 and in2 to the arduino pins? because i have a similar single relay board, and i could get it to work without a transistor.

DMond:
hi,Grumpy_Mike is a transistor necessary? cant he just connect the GND and VCC input from the relay to an external power, and the in1 and in2 to the arduino pins? because i have a similar single relay board, and i could get it to work without a transistor.

No you are mixing things up. A relay only has two wires, to turn it on you need to pass current through those two wires. If you connect them to GND and Vcc it comes on straight away and the arduino does not control it. What are in1 and in2?
It sounds like you have some sort of shield or driver with the transistor or other such driver on it.

The product (from ebay) mentioned in the OP's post is able to be controlled without using transistors. Just hook it up straight.

justone:
The product (from ebay) mentioned in the OP's post is able to be controlled without using transistors. Just hook it up straight.

That board has a transistor on the board already!!!

Well who would have thought?

From the product description.

This is a 5V 2-Channel Relay interface board, Be able to control various appliances, and other equipments with large current. It can be controlled directly by Micro-controller (Arduino , 8051, AVR, PIC, DSP, ARM, ARM, MSP430, TTL logic) .

•5V 2-Channel Relay interface board, and each one needs 15-20mA Driver Current
•Equiped with high-current relay, AC250V 10A ; DC30V 10A
•Standard interface that can be controlled directly by microcontroller (Arduino , 8051, AVR, PIC, DSP, ARM, ARM, MSP430, TTL logic)
•Indication LED’s for Relay output status