I want to control a remote control that is used to lock/unlock the doors of my car. I have taken a spare remote control and added leads to the on the remote that when connected activate the remote. The remote has a small 12v battery and when the two leads are connected the remote signals the lock/unlock control box.
Due to space limitations I want to use an Arduino Nano and a N-Channel Mosfet but I am unsure how to wire the Mosfet as a switch connecting the two remote leads. If a Mosfet won't work, I'd appreciate suggestions for alternatives
[u]Here is a MOSFET driver[/u] that can be used as a DC switch. Note that it's the ground-side that's switched. You can probably leave-out the diode since you have a non-inductive load.
Are you switching power on and off?
Or are you sorta hijacking some button contacts: the remote is always with battery, but you are simulating a button press by shorting the button contacts?
Different answer each case, so.
a7
Think about possible EMI/RFI shielding requirement so it dosen't mess your car up, especially if you're hijacking a system
I am using Arduino to simulate pushing of the remote buttons
See this
https://forum.arduino.cc/index.php?topic=312951.0
I think you want to use a 74HC4066. I’m guessing the buttons are in a scanned matrix on the remote. If they all just connect to ground you could use a transistor.
Or, simpler and fool proof would be to just use a small relay driven by a transistor hooked to the Arduino. The relay method means there’s no need for any electrical contact between the two devices.
Do you anticipate wanting to control more than one button?
a7
here's the issue. I have a very limited space to put this in, There are 8 buttons all together. I looked at using 8 standard type 5v relays but way too much room. That's why I am looking for a 'smaller' solution.
Thanks for helping me out
Can you tell how the switches are in the remote circuit? Like a matrix or separate connect to ground or…?
Take a few pictures and show us. The 4066 part looks so far to be what you want.
a7
Is this what you are trying to explain to me? The push button represents the remote button I'm bypassing.
A 5v Arduino Nano will be used. The resister 1k ohms. The remote has a 12v battery. I'm not sure of the transistor but from what I've seen will a BC337 work?
I would rather opt for a small mosfet, maybe even a switching IC with all switches onboard, you need to know the voltage you are working with before selecting one, batt may be 12V or 1.2 but the voltage at the switch/circuit can be different.
I highly doubt its 12V since it deals with logic, would make for the weirdest remote ever, measure it... also check your top left button for continuity because it looks soldered shut from here.
Still I don't quite get what you are trying to achieve with the nano?
smartphone connectivity to the key?
I thought you were building a whole remote system for a car that doesn't have one, but has central lock xD
Or will you keep the "crappy" remote in the car and build a better system, then why not interface directly with cars UHC module?
The transistor in #10 shows up quite a bit, but it depends on the switches having a common side to ground, other wise separate. The pictures don’t make it clear.
Are you forming “presses” by shorting one wire from the switch (one at a time) to the remote’s ground (negative battery terminal)?
Otherwise, if the switches for a matrix or are otherwise oddly wired in there, the 4066 part and the technique shown in the link should be used.
I can’t find what a UHC module is. Hijacking a remote is fun, and it takes care of any security measures that you’d have to hack if you are simulating the packets it transmits.
If this UHC is easy to talk to, creating a remote to do so would be fun, too. More different fun, different merit badges at the end of it all.
a7
The way the remote works is you push one button at a time. This causes one of the colored wires to connect with the black wire - i.e. for 6 buttons, 6 colored wired and one black. For my drawing above there would be 6 transistors, while I just showed one
Okay, assuming that the black wire is the remote ground, you can use a transistor for each switch, as has been seen.
The ground of the remote connects to the ground of your circuitry.
The transistor isn’t critical, any small signal NPN should do. I bought a giant bag of cheap 2N3904s long go, use them for everything. The resistor 1K isn’t critical either, I use 4K7s, e.g..
Ppl use MOSFETs here, that’s fine too, I just don’t have a giant bag of them. This is not a critical deployment, there is no real reason to use one over the other.
a7
Thanks - I just order a box of various transiters from Amazon - 10 different types and 25 of each type for $8. I'll let you know how it goes
OK. Almost any NPN transistor should work in this circumstance. Like I said, I just happen to have 2N3904 and its sister 2N3906 on hand from some years ago - never mind how long precisely.
I have used them everywhere you see the usual uncritical transistors of this ilk.
Probably paid a bit more than $0.032 each, but not much!
You might want to wire up a few experiments once you get the transistors in.
a7
If you know the voltages, no more than 5 V, and the particular connections to each pad then a 74HC4066 would be more appropriate than transistors. 
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