Auto Window Rollup

This project is very simple but quite useful. You can make your power car windows roll shut on their own when the car is off and the door locks are activated. There may be some adaptation necessary as this was designed with the wiring of a 2002 Ford Explorer in mind; however most cars will work with this circuit as it is.

The requirements I designed for were these:

  • A time limit for which to roll the windows up once activated (prevents things burning out).
  • An optional end-of-travel switch so power to the window is disconnected immedately as it reaches a closed position. (further prevents things burning out).
  • An automatic auto-rollup disable when the accessory power is on (so if you hit the locks your windows don't roll up while the car's on; useful for car with self-locking doors above certain speeds).

 

This is implemented as in the schematic below using three transistors, two relays, and a small handful of cheap components which one can obtain almost anywhere or even salvage out of recycled electronics.

This circuit is based on a timer composed of a series RC (resistor-capacitor) circuit and a number of transistor switches to create the correct logic function to make the circuit operate as desired.

RY1 is a Form A or  normally open relay and serves to energize RY2 which causes the window to roll up by closing the connection between Battery + and the UP wire to the window motor. RY2 is a Form C or DPDT (double-pole double-throw) relay which normally keeps the UP switch connected to the UP wire on the motor. If the relay is energized it breaks the switch connection and operates the motor. The diode D5 is provided as a failsafe to allow the window switch to work even if the relay should be damaged; it also prevents back-EMF generated by the motor from burning the relay contacts.

S1 is the end of travel switch and it completely disables RY2 if it is closed. You can use a normally open or normally closed switch for S1 depending how you fit it to the window; the rule is that is must be open whenever the window is closed.

The lower portion of the circuit with the transistors is the important part; it provides the delay and lock-pulse sensing ability.

Q3 serves as a system enable switch by checking to see if Accessory Power is active; if it is, the transistor is turned off and will not allow RY1 to energize under any condition. If Accessory Power is inactive, the 10K resistor on Q3's base causes the transistor to allow current for the relay if Q1 ever turns on. D1 is not necessary for the circuit to function but is included as a safety; I might later remove it after I've thought about it some more.

The 100µF capacitor and 100K resistor form the timer portion of the circuit. When the central locks are pulsed to make the locks move  the diode D2 gets forward biased and charges the capacitor immediately. Once the pulse is finished the capacitor remains charged for a while as its only discharge path is the 100K resistor. This charge is enough to keep Q2 turned on for a while. Q2 turns on Q1 which serves to energize RY1 (providing Q3 is on via a lack of Accessory Power) and roll up the windows. 100µF and 100K give around a 10 second delay and can be altered for longer or shorter time periods.

Diodes D3 and D4 are to prevent back-EMF from the relay coils from damaging the transistors and/or generating EMI/RFI emissions.

Alternate Configurations

The car I designed this for had active-high window motors and power locks. What this means is that a positive voltage is connected to the motors and lock solenoids to make them work, instead of connecting them to ground as some systems (active-low) work. If your vehicle is one of the latter then you will have to alter things somewhat to allow for this.

For example, if the UP switch connects the UP motor wire to ground then you'd have to reverse D5 and connect the normally open pin of RY2 to ground instead of Battery +. If you do this, you must connect the line from RY1 and Q1 to Battery + instead of leaving it on the normally open pin of RY2. The circuit would now connect the UP motor wire to ground to activate the window.

If the lock motors are pulsed to ground then it gets more tricky; you'd have to use a PNP transistor for Q2 and reverse D2 while also moving the 100µF capacitor to connect to Battery + instead of ground.

If you can't figure out how to alter the circuit for your car you may wish to email me (look for the "Contact" tab on my homepage).

 

I hope this circuit is of some use to someone!

 

Cheers


Previous page: Schematic and Description
Next page: CRT Fun