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I'm working on an Arduino project involving an UNO. I'm powering a 20x4 LCD screen and I am using all the ports on the Arduino, to the last.

All but four of them are pulled high at any given time, so by the time I'm done with pulling them all up the screen is going dim when powering via USB. So I tried powering via an external 9V 600mA adapter, but that makes the Arduino overheat and eventually shut down. I then tried another, 12V 500mA adapter, and that one doesn't even get my UNO to the end of the setup function, and it reboots repeatedly.

Anyone got good advice? Ideas?

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    Stop trying to burn out the MCU. – Ignacio Vazquez-Abrams Dec 31 '14 at 5:05
  • It's worth adding a schematic / daigram of what's connected. It sounds like you're trying to draw too much current from the outputs, normally an LCD shouldn't draw much current unless you're also using the backlight? – PeterJ Dec 31 '14 at 5:11
  • Use a 5V usb power supply, which allows you to bypass the voltage regulator, which is overheating. – Passerby Dec 31 '14 at 5:22
  • Maybe an inadvertent short path somewhere - this should not happen. Schematic and/or photos helpful. – bigjosh Dec 31 '14 at 16:48
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    Is it a 0.6 mA or A? That's a huge difference! If it's 0.6 mA that's not nearly enough to power an Arduino with a LCD. I assume that's a typo. – Anonymous Penguin Dec 31 '14 at 17:05
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The official arduino uno schematic uses a NPC1117 voltage regulator. This is a linear one. This means that if you put 12V on it, and if your system requises 0.5A, you Will leak 0.5A on the 12V, and, if there is 5V on the output, 12V on the input, there is a 7V drop on the regulator, 7V * 0.5A = 3.5W that turns into heat.

To avoid overheating, the solution isn't to increase the input voltage, but to decrease it. If you have a 6.2V power supply, this will minimize overheating. At least 6.2V are required for the NPC1117 to provide a stable 5V.

An other option is to use a USB 5V power supply with an output current greater than 0.5A. This is often used with smartphones. This allows to bypass the NPC1117, but the power supply shall be exactly 5V (where exactly stands for less than 10% of over or undervoltage).

Also, please note:

Arduino does not recommend bypass[ing the] Vin supply to directly supply 5V rail on the board as it will damage the NPC1117. See the first two line on page # 3 from the document link below. http://media.digikey.com/pdf/Data%20Sheets/Arduino%20PDFs/ArduinoEthernet.pdf You can either do the soldering and remove NPC1117 chip before you apply 5V directly onto the board or find a higher current capability power supply with the output voltage between 7v-12V.

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    Go with Jacen's second option. If you need any decent power, it's much better to skip the regulator on the arduino and just send it 5 volts directly, and since there are tons of USB power supplies out there, it's easy to find one. – Eric Gunnerson Jan 1 '15 at 1:02

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