KY-019 5V Relay Module


Arduino KY-019 Relay Module is used to control AC circuits, the relay acts as a switch that responds to a signal received from the Arduino, it has an integrated LED that indicates if the signal is high or low.  

Commonly used in IoT projects to control lights and other electronic appliances.



The KY-019 consist of a 1MΩ resistor, a LED, a 1N4007 rectifier diode and a 5VDC relay capable of handling up to 250VAC and 10A.

On the DC side of the board there are 3 pins for signal, power and ground. On the AC side there are 3 contacts, NC (Normally Closed),  Common and NO (Normally Open).

TTL Control Signal5VDC to 12VDC (some boards may work with 3.3)
Maximum AC10A 250VAC
Maximum DC10A 30VDC
Contact TypeNC and NO
Dimensions27mm x 34mm [1.063in x 1.338in]

KY-019 Connection Diagram

For the DC part of the circuit connect S (signal) to pin 10 on the Arduino, also connect the Power line (+) and ground (-) to +5 and GND respectively.

On the AC side connect your feed to Common (middle contact) and use NC or NO according to your needs.

NO (Normally Open) will get power when (S) is high, NC (Normally Closed) gets disconnected when (S) is high.

Always be very careful when experimenting with AC, electrical shock can result in serious injures.

KY-019ArduinoAC Device
SPin 10 
Common Feed In
NO  Feed Out
Arduino KY-019 5V relay connection diagramclick to enlarge

KY-019 Example Code

The following Arduino sketch will turn the relay on/off every second. We'll connect a desk lamp to the relay using the NO (Normally Open) connection so the lamp is off when the relay is off. Running the sketch will cause the lamp to light up intermittently. 

int relay = 10;  //Pin 10

void setup() 
	pinMode(relay,OUTPUT);  	// Define the port attribute as output 

void loop() 
	digitalWrite(relay,HIGH);  	// turn the relay ON
								// [NO] is connected to feed
								// [NC] is not connected to feed

	digitalWrite(relay,LOW);  	// turn the relay OFF
								// [NO] is not connected to feed
								// [NC] is connected to feed
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3 days ago

Hi, the .fzpz file has an issue : I’ve ordered a PCB and the GND pad has no hole on the PCB. On Fritzing forum, an expert (I’m a very beginner) said “the GND pad needs a ring pad on top of the square pad”.
Idem actually for your KY-012 fzpz file.
I hope you can generate corrected files (as I don’t know how to do that myself), because it’s really great to get those parts for fritzing.

27 days ago

I’ve 2 modules, both have the same problem: The voltage starts to swing, once the relais is switching through.

Guliano Giuli
Guliano Giuli
3 months ago

Please to supply data about current in milliamperes required for operation with 5 Volts.
Giuliano Giuli

David Hehman
David Hehman
1 year ago

This is great. Thanks for creating. I have a slightly different relay and would like to modify this to match. Would you be willing to share your SVG files with me? I will do the same when done.

2 years ago

Hi, nice article, but not sure where you got your specification for the KY-019 module from, it is incorrect. The additional components are: a diode, an LED, a 150 ohm resistor (current limit for the LED) and a transistor the LED + resistor. The LED comes on when the signal is HIGH (5V).

This PDF should have the correct schematic in it:

Also, maybe the relay as a single component can be triggered by 5-12V, but it is likely that the LED would burnout with 12V with the KY-019 (?)

Hope this comment helps others who come to this page 🙂