How2 control CarPC from key fob....
I came up with this solution for controlling my CarPC, I have not fully tested it yet. It was designed for my alarm, PC and set up and based on measurements from these. It is a very simple design and costs about $8 but I think it will work very well. I have not seen this design before.
Please use whatever you can from this, I think most is applicable to anyone with central locking and using an inverter, other parts will be useful for people running DC-DC solutions but need a shutdown and boot solution. Trying to give a little something back to this forum as I have learnt so much from it!
The circuit allows car PC to be switched on and off when the central locking is locked and unlocked from you key fob.
It automatically waits for pc to hibernate and then turns off the inverter (also the screen and amp if you want, I have decided against this and will turn them on and off with alarm directly, see limitations for reasoning). It still allows you to switch PC on and off using standard PC switch.
It knows if PC is already on or off. i.e if car is relocked when already locked PC will not turn on! (my alarm relocks doors if it gets scared by something).
It ‘waits’ for inverter to power up before pushing the on button. No relays are charged when Car is locked.
I wrote the following sequences mainly to check for myself it will do what I designed it to. Maybe they will help to explain how it works. Please let me know any mistakes, or improvement ideas.
Sequence 1 turning PC ON:
PC is off; car is armed (locked). Relays are all unpowered and open.
Unlock car from fob, negative current from doorlock interface activates relay B powering inverter etc.
Inverter takes 1 second to power up, when it has it supplies power to PC. 6v line from PC power supply becomes live (this is the feed which is used at the standard PC on/off switch, it is live when ever there is mains fed into the power supply, it can be taken from the the live side of the power switch, the mother board, or preferably directly from power supply).
This activates relay C which turns on the PC by jumping the standard on off push switch.
PC 12V (yellow) becomes live powering relay A and D.
Negative feed from doorlock interface stops (in my car this is 0.8 seconds after it is activated, but can be set to 3seconds which should be good for this use. This means on/off switch will be connected for about 2 seconds which is fine)
Relay B disconnects, however relay A has taken over supplying power to inverter etc.
Inverter, screen and Amp all on, Pc is on.
PC can now be turned off by pressing the standard switch, this will also shut off screen and amp and inverter.
Or leave on until you arm the car.
Sequence 2 turning PC off:
Get out car leaving MP3’s playing, arm car (lock doors). Negative feed from door lock interface is fed to Relay C coil via relay D (for 3 second in my case). Relay C activates which shuts down PC. Relay A stays closed until the PC 12v goes dead, then disconnects inverter etc.
Everything is off coils in relays are dead, no power is being used.
Sequence 3. ‘Relocking’ and REunlocking:
If doors relock, either by you pressing lock on fob again or by the alarm if shock sensor is triggered etc, when already locked (PC being off) the negative feed is terminated because relay D is open. Nothing happens, PC remains off.
If you unlock doors when they are already unlocked (PC is ON) the negative current feed will be terminated at relay D as this will be closed, It will activate relay B for 3 seconds but this don’t matter.
Pc stays on.
If PC hangs on shutdown. (I am not too bothered as inverter will turn off at 10.5V and am running 2 batteries). This would leave Amp and Screen and inverter on until dead battery or inverter shuts it self off. For this reason I am going to switch amp and Screen via a separate relay activated by a direct feed from alarm.
If for some reason you lock the car, then immediately unlock it again before PC has shut down it will carry on shutting down. It can then be booted by pressing the normal on off button.