Headlight reminder for cars
I have just had an embarrassing situation in that the internal
lights on my car were left on for three days, flattening the battery. This has
cost me a new battery, a lot of lost time, plus the wrath of the other family
member. So after a cursory examination of the "Headlight Reminder For Cars" kit
(SILICON CHIP, August 2001) at my local
Jaycar store, I purchased one.
However, I now believe it will not do what is required of it. I
have three separate circuits in the car which need monitoring: headlights,
parking lights and interior lights, as these are on separate switches, as well
as the door switches.
The first two I can monitor by taking a feed off the instrument
lights. I do not know about the third circuit but I wondered what would happen
if I put a diode between the door switch circuit and the light circuit. Please
advise (P. D., via email).
A diode from the
door switch and another from the interior light switch could be used to detect
when any light is on. The direction (polarity) of the diodes depends on the car
If one side of the lamps is directly connected to the chassis,
then the diodes connect with their anodes to the lamps where they are powered by
12V. The cathodes connect together and form the connection for the door switch
input on the Headlight Reminder. In this case LK3 is out, LK4 is in and LK5 is
Conversely, if one side of the lamps is directly connected to
12V, the diodes are connected with their cathodes to the negative side of the
lamps. The anodes form the connection to the Headlight Reminder and LK3 is in,
LK4 is out and LK5 is out.
Extending the SC480’s low-frequency response
I am using a pair of SC480 amplifier modules from the January
& February 2003 issues of SILICON CHIP. I know
that the SC480 module has excellent low-frequency response but I am hoping to
improve the response at near DC to facilitate another mode of testing. I’ve
built a vibration-testing platform and I am using the SC480s to drive the
Studying the circuit diagram, I can’t find the components that
are limiting the low frequency gain. Any help on this matter would be very much
appreciated. (J. M., via email).
Improving the bass
response below the existing -1dB point at 14Hz is simple. Just increase the
input 1μF BP capacitor to 2.2μF or 4.7μF. Similarly, increase the 47μF BP
feedback capacitor to 100μF or 220μF.