My UNO has been running through the usb cable. I disconnected it and connected to 12v 1.5 amps and it is malfunctioning. It uses a rtc to operate a servo and mp3 player. The servo runs immediately as does the mp3 player regardless of the time shown on the lcd. When the mp3 player finishes the speaker makes a very loud static noise. I measured the voltage and it is 12.4 v.
It works fine when connected to the computer using the usb port.
What could be wrong?
Suggestions have popped up and I will try 9v.
Hi, @richardvanraay
What is your 12V 1.5A powers supply.
Can you please post some images of your project?
So we can see your component layout.
Do you have a DMM? Digital MultiMeter?
Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.
Thanks.. Tom.. 
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External devices should always be powered by their own external power supply.
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Your circuit works with USB power because the on board voltage regulator is bypassed.
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When the power jack is used, the onboard regulator is used but your 12v input will make the regulator fail if too much current is taken from the 5v pin.
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The Arduino onboard regulator is meant to power only very light loads.
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Thanks Larry, I think I stuffed it completely. I have tried a new UNO and there is no time, just 0.00. Shivers I am disappointed. I think I fried the rtc. The external power source was bought at Jayco (Australian electrical supplies). It is 12v 1.5 amp. There is one servo, one thermometer and one lcd, one small speaker, being powered from the 5v on the Arduino. I thought this would be quite okay, maybe not.
Even that does not work now. The thermometer does but not the rtc. S, S, S.
Thanks Tom but I would not know where to start with a diagram. There is a shield with the mp3 player and rtc soldered on to it. They are soldered to the 5v output.
I might have to start again. s. I was just about to place it in the garden next to the gnome.
It was working for two days through the usb. Even that does not work now. The thermometer does but not the rtc. S, S, S.
The mulimeter shows 12v from the wall plug transformer.
Dismantle what you have done and check the individual parts work ok .
Use simple program , eg blink on the uno and see if it works on both usb and your power supply .
Then try the rtc with an example program .
A picture of your setup and links to the bits would help .
If you use a 12v input and then drive a servo from the 5v output , it’s likely you will over heat the on board regulator as previously mentioned . Servos need to be powered separately.
Have a google on how to draw a schematic on paper
If you destroy a UNO always check what is wrong with the circuit and when you understand what is wrong correct it . UNO’s very very rarely fail of their own accord , so dont just try another
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Thanks very much hammy for your detailed response. It will be very helpful and has some great tips.
I have started from scratch, gosh it is dissapointing as it has taken me months. So far I cannot even get a rtc and lcd going.
In another post Larry D was suggesting using different pins and someone was suggesting using milliseconds instead of delay and such. I will probably take a few months again to sort it. I just hope the same thing does not happen.
I will try to draw a schematic over winter, it is summer here in Tasmania, on Tinkercad and ask the Forum for advice before I blow it up again. I am at a loss to why it happened.
I was going to have a seperate power supply for the servo but it is only one. I will check the draw on the speaker but I am fairly sure it is low as is the rtc and LCD.
It is such a shame as it had worked for two days. It is a fish feeder with mp3 and it calls out "Here fishy, fishy, fishy" before releasing the food. I have the gnomes house made and him with a fishing rod. It was ready to go in the pond today!
I really appreciate your tips.
Cheers
Richard
G'day Tom, what program do you suggest I try to learn to get a schematic diagram together? I had a quick look at Tinkercad but it does not appear to have all the hardware (?) I am using.
Cheers from Tassie.
Richard
A quick fix is to use a 5volt cellphone charger, connected to the USB socket.
That way you can get things working again, but you should power the servo and MP3 player from a separate 5volt source. That could be a second 5volt cellphone charger with the plug cut off.
Leo..
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even the mp3 player! That suprises me.
I will have the servo, mp3 player, speaker, thermometer and LCD all on a seperate power supply, although I have just ordered an mp3 shield. Anyway, I think my next step is to find an easy program to draw a schematic and learn how to do that.
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Cheers!
Just do an abstract drawing with boxes representing the parts and how the supply wires connect everything up.
Write on the boxes what each device requires in Voltage and Current terms if possible.
I know the UNO has a 7 to 20V range, but I would be inclined to use an external Voltage regulator to reduce this down to something like 9V. Any time there is a large dropout Voltage you will have heat problems which may damage the board. You could of course just use an external regulator to drop it down to 5V and use the USB port.
I am presuming this is the power disconnecting. To avoid this attach a smoothing cap and a decoupling cap, on the supply, close to the MP3 player.
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When powered with 12V the Uno can deliver barely any extra power to peripherals.
Energy burned off in the regulator is (12-5)*I W; the limit is <1W, safer 0.75W so maximum current I = 1/(12-5) = 0.14A = 140 mA, and the safe limit about 100 mA. The Uno by itself uses about 70 mA so just some 30 mA left. Go over the limit and the regulator overheats and shuts itself down, switching off the Arduino as well.
An RTC uses 1-2 mA or so, that's fine. Temp sensors similar.
An basic MP3 player probably uses something like 100-500 mA, depending on the type, and whether it powers a speaker or connects to an external amp, etc.
A servo 0.5-1.5A depending on the type.
When USB powering you have some 500 mA available, and you can get away using that for a small servo like the SG90. No overheating issues there but still not a good idea for more permanent projects.
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There are a number of different packages, as I am sure you are aware, like tinkercad, however there is a decent one called Kicad that has been around for some time now and has extensive libraries of parts and footprints.
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