Electrical Interior lighting tap for gauges - issues discovered and solved
#1
11-21-2016, 07:06 PM
Interior lighting tap for gauges - issues discovered and solved
Hello everyone.
This is more of an informational - FYI posting.
Recently I designed and made a power-and-light PCB for my silly project.
The concept was this: make a compact board that would have multiple plug-outlets that would switch on with the ignition to provide power and ground to whatever was plugged into it, and pass through a 12V signal correlating to the headlights or drl's/parking lights being on to dim the gauges at night.
Now, for the light reference I first tried tapping the 'luminous ring' around the cigarette lighter port.
Odd thing is the innovate gauges flickered when I turned on the headlights! The stock gauged looked fine, as did the 'luminous ring'
so I tapped the light for the tachometer as some installs suggest, same thing.
At this point (seeing as other mini-specific gauge installs call for tapping these locations) I decided to bench-test my board to see if somehow I was getting power related noise in that signal.
Nope. Hooked the board up to my variable DC power supply, and it worked perfectly!
(phew! board works at least! 
)
So, I decided to nab an Oscilloscope from work.
And after a brief self-taught lesson in how not to use it, I got it right and turns out the prediction I formed while driving to work that day was correct, the interior of the mini in 03 was lit with LED's in the dash and were dimmed not with a variable resistor, but instead PWM (pulse width modulation) And apparently the innovate gauges DO NOT like a pwm signal (even on 'full power' ) as their 12v light trigger.
for some pictures.
I had a dead battery, and the charger I had put a lot of noise into the circuit (sort sinusoidal), so instead I 'powered up' the car with my variable output power supply set to constant current at 13.2V (up to the units max of 5A)
In order to limit current throughput, I pulled the headlight relay, just in case I flipped the light **** 1 notch too far.
the power board that I made. Supports up to 20A power, switched through 2 relays. It's a 4 plane board with the middle two layers being power and ground planes.
Has (5) 3-pin outlets for +,-,light, and (2) ports with just +,- for powering solenoids. Ports are all individually fused, but most should run on 2A fuses (a select 1 or 2 have 5A fuses, like my wideband which needs the extra current for warming the sensor on startup)
excuse the mess, testing - o scope hooked up to ground pin on board and light signal reference.
O-scope at low interrior lighting setting
med-low setting.
med-high setting.
high setting.
even on the high setting I was still getting the gauge flicker!!
oh well,
This is the signal when I tapped the front drivers running light.
nice and clean!
and the tap in question. - black and green stripe wire
and now the gauges do not flicker!
Unfortunately the flickering does not show up on video due to the refresh rate of the camera on my phone, but this video shows the PWM of the interior lighting circuit.
TLDR/ TLDW :
If you tap an interior signal to dim your gauges and they flicker. Run a line through the firewall and tap a running light instead. The interior dash / running lights are dimmed with pulse width modulation and that messed with my innovate gauges.
This is more of an informational - FYI posting.
Recently I designed and made a power-and-light PCB for my silly project.
The concept was this: make a compact board that would have multiple plug-outlets that would switch on with the ignition to provide power and ground to whatever was plugged into it, and pass through a 12V signal correlating to the headlights or drl's/parking lights being on to dim the gauges at night.
Now, for the light reference I first tried tapping the 'luminous ring' around the cigarette lighter port.
Odd thing is the innovate gauges flickered when I turned on the headlights! The stock gauged looked fine, as did the 'luminous ring'
so I tapped the light for the tachometer as some installs suggest, same thing.
At this point (seeing as other mini-specific gauge installs call for tapping these locations) I decided to bench-test my board to see if somehow I was getting power related noise in that signal.
Nope. Hooked the board up to my variable DC power supply, and it worked perfectly!
(phew! board works at least! ) So, I decided to nab an Oscilloscope from work.
And after a brief self-taught lesson in how not to use it, I got it right and turns out the prediction I formed while driving to work that day was correct, the interior of the mini in 03 was lit with LED's in the dash and were dimmed not with a variable resistor, but instead PWM (pulse width modulation) And apparently the innovate gauges DO NOT like a pwm signal (even on 'full power' ) as their 12v light trigger.
for some pictures.
I had a dead battery, and the charger I had put a lot of noise into the circuit (sort sinusoidal), so instead I 'powered up' the car with my variable output power supply set to constant current at 13.2V (up to the units max of 5A)
In order to limit current throughput, I pulled the headlight relay, just in case I flipped the light **** 1 notch too far.
the power board that I made. Supports up to 20A power, switched through 2 relays. It's a 4 plane board with the middle two layers being power and ground planes.
Has (5) 3-pin outlets for +,-,light, and (2) ports with just +,- for powering solenoids. Ports are all individually fused, but most should run on 2A fuses (a select 1 or 2 have 5A fuses, like my wideband which needs the extra current for warming the sensor on startup)
excuse the mess, testing
- o scope hooked up to ground pin on board and light signal reference. 
O-scope at low interrior lighting setting
med-low setting.
med-high setting.
high setting.
even on the high setting I was still getting the gauge flicker!!
oh well,
This is the signal when I tapped the front drivers running light.
nice and clean!
and the tap in question. - black and green stripe wire
and now the gauges do not flicker!
Unfortunately the flickering does not show up on video due to the refresh rate of the camera on my phone, but this video shows the PWM of the interior lighting circuit.
TLDR/ TLDW :
If you tap an interior signal to dim your gauges and they flicker. Run a line through the firewall and tap a running light instead. The interior dash / running lights are dimmed with pulse width modulation and that messed with my innovate gauges.
