Question 1

How is this compatible with raspberry pi if it is 5v ttl? can i connect it to a raspberry pi and what voltage level activate it?

Accepted Answer

There's a driver circuit per relay on the board. The IN1 through IN4 inputs can be driven by a 5V or 3.3V logic signal, but the board needs to be configured properly. In my case the relay inputs were connected to the 3.3V GPIO outputs of an ESP8266 NodeMCU board. For 3.3V drive levels, do this: 1. Remove the jumper on the relay board between JD-VCC and VCC. 2. Connect VCC on the relay board (which powers the input circuits) to the 3V3 of the NodeMCU or Raspberry Pi GPIO Expansion connector. 3. Connect JD-VCC on the relay board (which powers the relay coils and driver circuits) to VIN of the NodeMCU or 5V of the Raspberry Pi GPIO Expansion connector. A logic low level on the relay board input activates the corresponding relay. A logic high level on the relay board input or floating input leaves the corresponding relay deactivated. Each relay consumes 68mA from JD-VCC (for the driver and relay coil combined) when one relay is in the activated state. So, when one relay is activated that's 68mA, or 4 * 68mA = 272mA from JD-VCC if all four relays are activated simultaneously.

Question 2

What is the third screw terminal for?  i know one is gnd in and the other is gnd to accessory, but the control pins are on the other side.

Accepted Answer

Answers claiming that the leftmost terminal is common are wrong. The center terminal is common, leftmost (shown connected to the center terminal with silkscreen) is NC 'normally-closed', and the rightmost of each triplet is NO 'normally-open'

Question 3

Can the arduino/rpi drive this directly or are external drivers required?

Accepted Answer

RPI=Yes.  The current flowing through inputs IN1 - IN4 comes from Vcc, a 5V supply and is limited by two diodes and a 1000ohm resistor so it will be about 3mA IF the picture here is the same as the board you receive.  
Board schematic: http://wiki.sunfounder.cc/index.php?title=4_Channel_5V_Relay_Module . 
More information you may need: According to the description here, the power supply will need to supply 50-60mA for each relay that is energized.  No, you will need about 100mA per relay.  The data sheet for the relay in the product picture http://www.datasheetspdf.com/datasheet/download.php?id=720556 says the relay coil requires 89.3mA.  This is only the current that flows through the relay coil.  Add to that the current the goes to the RPI and the current that drives the transistor that drives the relay coil and it adds up to about 100mA/relay. 
Hyetex

Question 4

Is diode stuff embed? do i need to hook it with external diode and pnp ect.?

Accepted Answer

External diode is embedded in the circuit

Connector Type	Through Hole
Contact Type	Form C Or Spdt
Current Rating	10 Amps
Brand	JBtek
Operation Mode	Automatic
Coil Voltage	5 Volts
Contact Current Rating	10 Amps
Maximum Switching Current	10 Amps
Minimum Switching Voltage	5 Volts
Specification Met	Ma
UPC	520361134553
Item model number	4450182
Item Weight	0.32 ounces
Product Dimensions	2.56 x 1.97 x 0.79 inches
Item Dimensions LxWxH	2.56 x 1.97 x 0.79 inches
Manufacturer	JBtek
ASIN	B00KTEN3TM
Is Discontinued By Manufacturer	No
Date First Available	June 6, 2014

4 Channel DC 5V Relay Module for Arduino Raspberry Pi DSP AVR PIC ARM

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