12V PWM gauge control

Other Hardware LEDs and Multiplexing
1

I'm using a tutorial to control an automotive gauge, It was originally a voltage gauge but I modified (Change a resistor) to be an oil pressure gauge (12V full scale), I can control it as it should, using a 2n3904 like this, without the POT and 12V instead of 5V, the 50k get replaced with a 10ohms to give 12V a full scale (it takes 0.03a):

Same connections, output pin 9, but also I'm using a Nokia lcd 5110 (exactly the same config. as the spark fun basic tutorial), as soon as I start both LCD and PWM gauge control, the LCD turns off and I think that its protecting, if I sweep the gauge on startup and then show some LCD text, it works, both things.. LCD gets off, am I doing something really bad? both arduino and gauge are powered by a 12V regulator, share the same ground. :astonished:

2

Nothing obviously bad.
Is your LCD using the same pins?

Otherwise it looks like it is not actually wired up like you think it is.

3

I'm doing something like this, without the pot on the nokia LCD and using a level shifter for the 5 to 3.3v on the arduino outputs (just like the adafruit page)

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4

So in fact not like that at all.

We need a schematic not an abortion like that of what you actually have.

5

I just replaced the 2n9304 with a TIP120 and works as intended.