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Tuesday, 24 February 2009

Headlight Reminder Circuit

A [...] solution is to go from the +12 Switched sidelight feed, via a buzzer to the drivers door light switch, you then need to put a diode in the door circuit to stop the other doors operating the buzzer.

    +12v  (sidelights)
|
+-+--+
| | Buzzer (12v)
+-+--+
|
+-------|<|-------- To existing drivers interior light switch
| Diode
|
O
----| Drivers door switch
O
|
Car Chassis

Thus when you leave your lights on AND open the drivers door, the buzzer sounds. If you mean to leave your lights on, just shut the door and the buzzer stops!


Connectors: D25 male
Resistors: 640k,320k,160k,80k,40k,20k,10k,5k,390 (+-1%)
(You can use different values of resistors, but the ratio of the values of the resistors must be same. 0.5, 1, 2, 4, 8, 16, 32, 64 etc.) 1, 2, 4, 8, 16, 32, 64, 128
Capacitor: Electrolytic or solid Tantalum 10 uF 10V

SCHEMATIC

        +---+
| 2 | ---<640k>---+
| 3 | ---<320k>---+
| 4 | ---<160k>---+
| 5 | ---<80k>----+
| 6 | ---<40k>----+
| 7 | ---<20k>----+-----+---- 10 uF -------> Out
| 8 | ---<10k>----+ |
| 9 | ---<5k>-----+ <390>
| | |
| 25| ------------------+------------------+
+---+ |
===
Ground

How to build

Solder all D25 male connector pins to corresponding D25 female connector pins (pin 1 to pin 1 etc) Connect the resistors according the chematic. It is maybe not possible to obtain exact resistor values. If you can't obtain them, try nearest values. <1%>

How to use

Connect this circuit to the centronics printer port of your IBM PC or compatible. Connect the printer cable to the D25 female connector of the circuit. Your printer should work correctly with this circuit and you can keed this circuit connected all the time. Connect the sound output to your stereo system. Line in and mic lines are suitable because the output level of this circuit is adjustable (about 0-2V PP). The sound quality is very good.

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