The main circuit using a single button, posted in the previous article can be witnessed below for reference purpose.
R1, R3, R6, R7 = 100K
R5,R8 = 2M2
R9 = 4K7
C1,C4 = 22uF/25V
C2,C3 = 0.22uF
RL1,RL2 = 12V/20AMP
ALL DIODES = 1N4007
N1---N4 = IC 4093
Now, as per the suggestion the window operation needs to be locked when all the doors are closed and the key switched in.
The above step could be implemented by adding the following design in conjunction with the above shown power window controller.
As can be seen, here we have effectively utilized the idle extra gate N4 from the IC 4093 and configured it with a few resistors and BJTs, for executing the proposed brake switch control feature.
The operations may be understood with the help of the following points:
When all the doors are closed, the relevant door switches also close and ground the positive available at the anodes of all the 1N4148 diodes. This immediately forces the input of N4 to go low due to the presence of the 1M resistor.
The low at the input of N4 renders a high at its output which in turn activates the BJTs, positioned as a switches.
However the BJTs would be still inactive as long as the positive from the key switch is not energized.
As soon as the ignition switch is keyed, the BJTs become functional and locks the motor flip flop stage by feeding a positive across D3 cathode. D3 has been introduced specifically here so that the locking potential affects only the flip flop and not the T1/T2 latch stage.
In the above mode the push button is rendered ineffective such that pressing it produces no effect on the window glasses which stays hard locked.
However the above situation gets restored each time the brakes are applied and held activated. Braking activates the brake switch, causing a positive potential at the input of N4 which in turn produces a zero at its output, switching off the BJTs. The positive at D3 cathode now becomes relieved so that the push button is enabled yet again for the intended window up/down operations.