Mazda Miata: Dimming for add-on gauges.

In article <4107fe42$0$65608$visi.com>,
Grant Edwards <com> wrote:
 

It may help you to know that the Miata dash dimmer works by varying the
duty cycle of the *ground* to each bulb--the "dimmer" is actually an
oscillator, not a potentiometer. All bulbs are always hot on the +12V
side.

Unless your aftermarket gauges have dedicated ground wires that do not
ground anything but the bulbs, you'll need to add a separate pot to dim
them by reducing the hot-side voltage.

--
Lanny Chambers, St. Louis, USA
'94C
the alignment page:
http://www.hummingbirds.net/alignment.html

Lanny Chambers wrote on 7/28/2004 13:21: 

Or add some electronics, e.g., an inverter with a capacitor.
Basically, just a transistor, and a couple of resistors and capacitors.
But you gotta know about electronics a bit, of course.
I've done that to dim my aftermarket radio/cd player. Works fine.

-Joe

On 2004-07-28, Lanny Chambers <net> wrote:
 

I know. I'm trying confirm which of the lines on the stereo
connector is the active-low PWM line, and which is the switched
+12V line.
 

My other sources indicate that they're not. The +12 side is
controlled by the "TNS" relay connected to the headlight switch
(it's what turns on the dash lights when the parking lights or
headlights are on). It's the labelling of "Pulsed Dimmer
(TNS+)" that is confusing. There should be one switched +12V
line and one active-low PWM line. The pinout I found has two
pins labelled "dimmer" or "dimming":

"Pulsed Dimmer (TNS+)" and "Inverted Dimming"

I'm trying to confirm that the former is the +12V line
controlled by the headlight switch and the latter is the
active-low PWM line.
 

They do.
 

Ick. If I did have that problem, I'd put an NPN transister on
the high-side of the bulb, and connect the base of the
transistor through a resistor to the active-low PWM line.

--
Grant Edwards grante Yow! ... I have read the
at INSTRUCTIONS...
visi.com

On 2004-07-28, Joachim Feise <net> wrote:
 

Why is a capacitor needed? Here's what I would have tried:

+12V
|
|
___ |/
PWM --vvv--| PNP
|\
|
Bulb
|
|
gnd


I think I said NPN in my previous post, but it should be a PNP

--
Grant Edwards grante Yow! A can of ASPARAGUS,
at 73 pigeons, some LIVE ammo,
visi.com and a FROZEN DAQUIRI!!

In article <41081b0f$0$65576$visi.com>,
Grant Edwards <com> wrote:
 

Right, that's what I meant to say. Sorry.
 

Then you can simply parallel each wire off an existing instrument
illumination bulb, no?

You engineers...always aiming for "elegant", when "easy" would get you
back onto the road quicker. Elegant is for winter projects, man! :-)

--
Lanny Chambers, St. Louis, USA
'94C
the alignment page:
http://www.hummingbirds.net/alignment.html

Grant Edwards wrote on 7/28/2004 14:44: 

To make the output smoother. The input is a square wave,
and I wanted not just invert the input, but flatten it.
A plain inverter would work in your case because of the slow
reaction times of light bulbs.
With my radio illumination all LED-based, I didn't want the
LEDs flickering, though...
I don't have an oscilloscope anymore, so I went more with
whatever I remembered from my college electronics class.

-Joe

On 2004-07-29, Joachim Feise <net> wrote:
 

I assumed that the frequency of the PWM was above that which
was visible -- the same way you don't notice fluorescent lights
flickering at 100Hz or 120Hz.
 

--
Grant Edwards grante Yow! I have the power
at to HALT PRODUCTION on all
visi.com TEENAGE SEX COMEDIES!!

"Grant Edwards" <com> wrote in message
news:41090854$0$65608$visi.com... 

Wow... I hadn't realized the U.S. had upgraded their electric supply
system.
Here in Canada, we're still at 60 Hz.

Pete
94BRG

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