Electronics > Beginners
Circuit to control car windows
(1/3) > >>
cs2000:
Hi guys.

Im looking at building a custom PCB (more of a "can I do it" than anything else) which will take a input from the car, through an Arduino to control my electric windows.

Essentially, the system will take the door lock pulse, then activate a relay for X seconds to close the windows when the car is locked with the lock button on the key fob.

As I want to maintain power to the system after the car is off for a moment or two, im adding in a LiPo charger PCB from Adafruit and a 18650 (which yes is probably overkill).

I have a very rough schematic which is the below. Would appreciate any advice on 1. will it work, and 2. anything else like resistors or capacitors to smooth out the voltages needed/a good idea. I will of course add in a fuse on the inputs, but il use a standard automotive blade fuse in line for that.



Also here is my parts list on digikey if you need to see more detail on any of the parts http://www.digikey.co.uk/short/jh84bh.

Appreciate any assistance on this before I pull the trigger and do a breadboard design. I later then to try and get a PCB from JLCPCB or something and try and make it that way!
Paul Price:
Looks like a wee bit of of overkill in your scheme to charge the li-ion battery, you could just float charge  it (charging always on when the ignition is on)  with a constant 4.1 voltage source (a single NPN pass transistor(some T0-220, i.e. TIP31) on a small  heatsink) with a zener diode to set the output to 4.1V) and then current limit the float charging current with a small wattage resistor in series with the collector of the NPN pass transistor. This 4.1 V charging voltage will never damage the LI-ion cell. Alternatively, you can use a LM317 to do the same float-charge job as the NPN transistor suggested and it would be much easier to set accurately the 4.1V float charge V.

To keep things simple, you could just use  a very low-standby power CMOS 555 timer to actuate the relay for the required number of seconds to close the windows and so do the same job as the overkill Arduino, but actuating the 555 at key turn off might require another 555 to keep the first 555 powered. I would probably use a 8-pin MCU like the 12F683 or func. equiv. to do the same job in one IC package since I know how easy it is for me to write the program to do this job, even with the necessity to add a resistor-zener voltage regulator to power the MCU, which would give very good protection from 12V car battery circuit surges.  The same MCU could easily measure battery voltage and manage float charging the li-ion battery.
sokoloff:
One thing to consider is whether your car is new enough to use CAN for communications and, if it is, whether you can accomplish this task more easily over CAN.

I'd put a CAN sniffer on the body CAN bus, activate the dock lock, key fob, and power windows. If all of those are present, I'd then try to emit a "window-close" or "window-auto close" CAN message and see if that worked to close the window. If it did, you have an all-CAN solution available, which will [somewhat counter-intuitively] be a lot easier than what you're proposing above.
Paul Price:
Complexity!  Just because you can CAN, doesn't mean you should!
bob225:
On GM cars its known as total closure other marks its known as soft or comfort closing

This is way over kill, you can do this on older cars with a 555 timer a few transistors and relays be aware that newer cars windows and locking are controlled via the bcm over can lines

Most CAN based cars have this sort of closing built in and it just needs enabling

15-20 years ago it was common to fit closing kits

a cheap Chinese close kit is under £10, a decent on is more like £35 - All they are is a cut down car alarm

Edit. What car and year ?
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod