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G8MNY  > TECH     11.12.18 11:00l 55 Lines 2279 Bytes #5 (0) @ WW
BID : 48944_GB7CIP
Subj: Delayed Interior Car Lamp
Path: ED1ZAC<ED1ZAC<IZ3LSV<IR2UBX<F1OYP<ON0AR<GB7CIP
Sent: 181211/0952Z @:GB7CIP.#32.GBR.EURO #:48944 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                   (Correction Jan 10)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Here is a circuit I used, originally based on a Maplin kit.

WHAT IT DOES
It holds on the interior light for 20-30 seconds after opening the door, but
immediately turns it off if the Ignition Switch is turned on, or the car Alarm
is armed.
                                               +12V
                                             Lamp
                                                1A
                       1M>Ĵ
             D1                             
Arm Alarm +>Ĵ>Ŀ     Ĵ>Ĵ            
                 4k7Ĵ   D3   4k7           
 Ignition +>Ĵ>          ____    ____    
             D2           /      / T2     
                       Ĵ T1  Ĵ TAB     o /Door
                      3k3  \e /   \e /      / Switch
                    C  +    Ĵ      Ĵ      
                   47u===      \e      \e    
                    6V     
                                    __       __
HOW IT WORKS
C is normally charged up to 1.2V & T1 darlington held on by the current through
the 1M, T2 power darlington (or VMOS FET) is held off.

Opening the door the lamp lights & C is discharged through D3 turning off T1.

Now on closing the door T2 is held mostly on (1.5V drop) through the 4k7 until
the C is charged up to 1.2V via the 1M. At C = 1.2V T1 is again turned on & T2
turned off. The addition of the 3k3 makes this a snappier action keeping T2's
heating down.

If either the Ignition or Alarm circuits are powered while C is less than 1.2V
it will very quickly charge up & the light extinguished.

LOCATION
This circuit does not need power itself, only an earth, so the location is not
too critical. If switched power lines like the Ignition & Alarm are at risk
with this addition, consider putting a 4k7 in series with each wire so that
accidental shorts to earth can't harm anything.

Note this circuit draws about 2.2mA all the time, & although a very small
current it may add to other loads on a parked car battery!


Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP


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