Hi, first time poster. I am after some help with a project. I bought a Rf module from here. I have it connected to a nano. I have a Rf remote fob similar to a garage door opener. This is all working great and logic works as expected. My issue is I am wanting the output to switch on an automotive relay (large current). So from my nano I have a resistor 880 ohm to the transistor base. The collector is connected straight to the 12v + and my automotive relay coil is connected to the emitter then to ground. I’m having some drama getting the transistor to turn on. I’m only getting about 4v on the coil, and obviously not enough. I only want it to be a momentary thing as I just need it on for a split second… any ideas would be great.
Thanks so much
Hi Ben
Welcome
For a start you have got the relay in the wrong place. it has to be in the collector side. The emitter voltage will only be 0.6V below the base voltage so as you are only driving he base with 5V about 4.4V is the maximum you would get at the emitter.
Secondly you need a diode across the relay coil or the back EMF will destroy the transistor.
What is the DC resistance of the coil and thus the operating current. The transistor will only supply a maximum of 600mA and although the 2N2222 is a very good fast switch it is not big on current.
I would personally use a Mosfet here as a low side switch. Series gate resistor about 1k to 3k3, not critical. Source to ground or battery negative and relay in the drain circuit to batt positive. Diode across relay still required, preferably schottky fast diode, cathode to positive side and anode to negative side or Mosfet drain. Connect 10k to 100k resistor from gate to ground to ensure gate capacitor discharges at switch off.
Important Nano ground MUCT be connected to Mosfet ground (you have shown this in your version.
Cheers Bob
Thanks for the reply. After I sent this through I had a long hard look at myself and worked out I had it on the wrong side haha. Thanks so much for that information I will swap over to that mosfet and go from there. Really appreciate your help.
Ben
Hi Ben
Don’t forget the diode across the relay. The Mosfet needs to be N channel and if switched from Nano has to be a “logic level” switching device.
Cheers Bob
Hi Ben
Add on
I note Core no longer stock this ut you will find a handy Mosfet board here.
The series gate resistor and gate discharge resistor are already mounted on the little board. Just 3 connections to make.
Cheers Bob
Hi Ben and Bob,
I’ve used Core’s replacement to great success: MOSFET Power Switch Module | Core Electronics Australia
You guys are legends. Thanks heaps. This is perfect 
Hi Liam
Had not seen that one. A bit more information would not go astray. That is about the thinnest lot of data I have seen. Personally would not plan on using it without more info.
Cheers Bob
Hi Bob,
Yeah from the SKU numbers it looks pretty new. Yes definitely very light on data, what kind of other stuff do you think is essential? Might be able to track down some for the guys at Core to add to the page.
Hi Liam
Connection info would be nice. Also a circuit so one can see what those resistors and LED are doing and what if anything needs to be added for different applications. Could be a useful addition to the arsenal of bits.
Cheers Bob
Hey Bob,
Thanks for the suggestions, I’ve added this to the list of product pages that need updating in our next round of changes on the website to add further content.
In the meantime, until it is up @Ben107345 and anyone else who has questions about the MOSFET Power Switch Module specs or how to use it, please feel free to send through your questions here or in another post.
Hi Bryce
Haven’t seen too much in the way of additional info to date.
Cheers Bob
Closing because it seems the OPs concern was resolved 
discussion about improvements for other products should be moved to a separate thread - please follow the link at the bottom of the product page.
