Rf module coil

Thread Starter


Joined Nov 16, 2022
Hi all,
I am very into electronics.
I was learning about relays.
Couple of questions popped up.
1. In normal one channel relay module- when you turn the switch on- the battery powers the coil which in turn shifts com to no.
Now in case of radio frequency 1 channel relay module- when i connect the battery- the red light is on. After i press the switch of my transmitter- then the com shifts to no.
The question is- despite being powered on by battery (red light on) is there any mechanism in rf module that keeps the coil off and only turns on/powers the coil after I press transmitter switch which causes com to no shift?
Could someone please tell me what that mechanism is?

2. If I want to control an led light woth rf relay module- in com which part should i connect? Positive or negative? And in case of no/nc which part should I connect pos or neg?
3. In which case do I need to use external power source in addition to the 12v dc battery in relay module eg: rf 433..
And in which case I can only use the source battery for both turning the relay and load on?

I will be forever grateful if you could answer me the questions. Thanks in advance


Joined Jan 27, 2019
Welcome to AAC.

It seems you have a fundamental misconception about the action of the relay. It would help a great deal if you could provide a link to the module you are trying to use. I am sure we can straighten things out for you but it’s not a good idea to try that flying blind.


Joined Jan 30, 2016
In the case of the relay module the input drives a transistor switch which turns the relay on - thus a very small current (input, maybe <1mA) controls a larger current in the relay coil (maybe 20mA) which switches the contacts (up to 10A)

In the RF module a coded signal from the transmitter activates the matching receiver which outputs a small current to what is essentially the same module as above. The receiver is on as long as the battery is connected but the relay is only activated when a transmission is received. Depending on how the receiver is configured the relay can be active only while receiving or toggled on and off by sequential received signals.

Does that help?

In the case of wiring a LED to either the relay or the RF module, it would be using the relay COM and NO contacts. By convention COM would be wired to the battery or power supply, which could be the same one as powering the module, and NO to the LED & resistor and then back to the other side of the battery or power supply. The relay contacts don't care which way round (positive or negative) as long as the circuit is complete electrically; convention usually puts the contacts on the supply side rather than the ground or return side.



Joined Jan 27, 2019
So NO stands for Normally Open. When the relay is not energized, there is no connection between COM (common) and NO. The NC (Normally Closed) is connected to COM.

When the relay is energized, the NC connection is removed and the NO to COM connection is made.

In order to make something turn on when the transmitter button is pressed, the positive side on it's power connection should be connected to COM and NO should be connected to the positive input on whatever you are powering.

So, when the relay is not energized, the power will be going from COM to the unused NC terminal. When it is energized, power on COM will be connected to the NO terminal.



Joined Jan 8, 2017
When I first read this thread when the TS said RF relay I took it to mean a relay that was designed to work with RF. For example the relay in a transceiver that switches the antenna between the receiver input and the transmitter output. Now that he has provided the link to the product his original question becomes clearer. The RF relay module is much more than just a relay. It is a relay (The large blue item.), A radio receiver and a microcontroller that decodes the signal from the transmitter. (The key fob.) and controls how the relay coil is energised. The control mode section of the link describes the three different modes of operation. The mode will be selected by changing the position of jumpers which I think can be seen near the bottom right hand corner of the picture if the module in the link. The link does not describe how to configure these jumpers. You will probably find this information from other sellers of this relay module.