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messer · Senior Joined: 08 Mar 2012 Posts: 2059 Location: Europe

Twilight Lights For Auto
To have become popular for homes and gardens switches that turn on the lights when night falls and go off with the arrival of dawn.
But it is rare to see this kind of circuits in cars, whether of the most accessible to the most expensive.
And one does not understand how a factory that is gaining a considerable sum of money for a vehicle is not able to place these devices are really simple and inexpensive.

As seen in the diagram the operation is really simple. The LDR (marked on the diagram as FR) varies its resistance depending on the light it receives. This attacks to an operational amplifier which is configured as voltage comparator. When the inverting input voltage breaks down on the non-inverting input of the output is energized causing the transistor to saturate and the latter driving the relay coil.

The 100nF capacitor must be located as close as possible to the IC. The input diode prevents an accidental reversal of polarity module dam-age.

The relay should have a 12v coil 1A and switch to modern vehicles (with relay of lights) or 20A for older vehicles (without relay of lights). Stated differently about vehicles built since 1980 have relays that command all heavy current electrical branch.
Then switches and controls the boards have to handle only small coil current required for each of these relays. In contrast, previous cars were used directly powering switches on electrical branch so these switches should be able to handle the current load. I
f you doubt that relay place, best place big one. The lack of current handling capability can bring problems, but has no objection to metal (except the size, of course).
Twilight Lights For Auto Twilight Lights For Auto

Twilight Lights For Auto Twilight Lights For Auto

The 10K potentiometer allows to adjust the darkness or lightness point where the drive module. Do not solder wires and take the knob to the board. And parasitic noise produced by the electronic injection system may interfere with the performance of the module.

It is important that the installation is done as follows:
The relay contacts are shorting (bridging) control key position headlights. So the key to the relay must be parallel with the vehicle's light control.

The module power must be obtained from the current supplying the vehicle engine. DO NOT CONNECT TO BRANCH OF LIGHTS OR RADIO.

If you were to connect the module to a branch that has power lights will flash permanently alone at night even with the car parked. However, if you feed the module from the branch that carries power to the motor, as the latter only works with us up (or so it should be) the lights will light only if the engine is running.