Arduino Uno Powering via LM317

Ok,
I built an digital dashboard for my car. It works and tested it heavily only using a 9 volt battery. Now that I am sure that it works, it is time to connect it to my cars power. It runs well off of the car battery, while the car is off, and I could of just placed a switch to turn it on or off. However I decided to use a old wire used to power the tape player that provided 15 volts so that when the car was turned on, so does the dashboard. I built a voltage regulator with an LM317 to bring the power down to 9 volts. However, the Uno seams to be powering up, barley, but the screen does not lite. Connecting it back to the battery while the car is running and through my voltage regulator gives the same result. Connecting it to the battery while the car is on and without the regulator fries the Uno (Lost my Mega to this). Even bringing the regulator up to 12 volts does nothing different. I am guessing the LM317 is reducing the current needed to power the Uno and screen. Any thoughts? Thanks.

P.S. I am attaching a picture of the circuit I built to regulate the voltage, R2 is not a 5k ohm resistor rather a 10k Pot to allow a non-fixed voltage regulator. Also Vin would be 15 volts once the car is running.

The LM317 is rated at 1.5A reading the datasheet… Have you checked the output
voltage is correct with a multimeter? Does it change much when you connect the Arduino?

MarkT:
The LM317 is rated at 1.5A reading the datasheet... Have you checked the output
voltage is correct with a multimeter? Does it change much when you connect the Arduino?

I was using a multimeter to set the voltages prior to connecting the Arduino. I just checked what it reads when the arduino is connected, I get -3.7 volts when I set the the LM317 to produce around 9 volts, disconnect the arduino, returns to 9 volts.

I actually may have found my problem. There is a small bridge of solder connecting the adjust and the Vout pins. Going to see if this resolves my problem.

That should fix your problem. :grin:

That was the problem. It would give me a false reading when not under load. Cleared the bridge and my regulator works. Thanks