I have an Arduino Uno, and I am making a game with an LED bargraph. I've never noticed until now that when my sketch to control the 10-LED bargraph is running several segments of the display, the ATMEGA328 gets noticeably hot. It doesn't seem to affect the performance of the Arduino, but it has scared me enough to unplug the Arduino and ask. Is there a particular reason why my Arduino is getting hot while using the bargraph?
JohnSmith41:
Is there a particular reason why my Arduino is getting hot while using the bargraph?
Yes, there is!
My psychic powers are telling me.... no current limiting resistors! Am I right?
But wait... your motto says "Best way to not fry anything: PUT RESISTORS ON EVERYTHING!"... but what value of resistors?
Sarcasm aside, give us a schematic, or a picture, at least a more thorough description. And check for shorts, if you have resistors on everything, that's the most likely reason for the overheating.
Paul
The microcontroller getting hot is bad.
You can buy a cheap ir infrared remote temperature meter on Ebay for 10 dollars. It helped me a lot to measure the temperature of components on a circuit board.
Well mine got really hot when I plugged in a 12 volt power supply to it. I think it had to dissipate in heat 7 of the 12 volts, so it got warm.
sensai:
Well mine got really hot when I plugged in a 12 volt power supply to it. I think it had to dissipate in heat 7 of the 12 volts, so it got warm.
The on-board 5V regulator, but not the microcontroller ('328) itself.
Well... johnsmith41 has not replied. I hope he is not bitter about my earlier comments. (That joke will only mean anything to the Brits here).
Yes the regulator.
if you have resistors on everything, that's the most likely reason for the overheating.
I remember telling him something similar a few weeks ago. --> White on Blue 20x4 LCD Module breadboard schematic and sketch? - #6 by floresta - Displays - Arduino Forum
Don
Being dragged from my Arduino... :<
Not sure on the value, since it came with an LED pack, but it appears to be brown gold black black brown. I have these resistors on all 10 segments, and all 10 of the resistors are then plugged into the Arduino, pins 12-2. I have an RGB LED on the board too, but when that is removed it is still hot.
Hi, do you have a Digital Multimeter?
An invaluable device, even the cheepo ones.
brown,black,black,gold, brown is 10 Ohms, tooo low..
Arduino outputs are being over loaded, (5-1.6)/10 = 340mA, way too much even for the LED.
For say 20mA per output, safe and probably the LED spec current.
(5-1.6)/.02 = 170 Ohm, so 220 Ohm for each output will current limit your output to the LED graph.
Tom..Hope this helps.... 
Better help with a colour code, TG.
220? is red-red-brown (gold is a tolerance band.)
330? is orange-orange-brown, resulting 10 mA.
Would connecting a 10k resistor from ground to a wire leading to GND on the Arduino limit the power enough?
Yes that would certainly limit the power. Enough to stop the leds lighting up completely.
Hi, John you haven't said if you have a DMM, if not even a al cheepo one of ebay will be invaluable when building projects.
Especially with resistors and the problems these days with poor manufacturers choice of body colour and try to read values.
Tom.....
I don't have one, but I am getting one soon. I have a coupon for a free multimeter 