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Author Topic: Strange behavior with power supply vs. computer USB power  (Read 1771 times)
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I'm debugging a problem with the Seeed music shield v1.0. I'm using an Uno. If I run things off of my computer's USB cable, all things work fine. If I connect a power supply, it can't init the sound card and opening MP3 files fail. I thought my power supply might be bad, so I bought another that outputs more power ( 1 amp). Any ideas on what could be wrong here? It's repeatable 100% of the time. I'm not sure what else to try.
JR
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The last thing you did is where you should start looking.
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With the power supply plugged into the Arduino, measure the voltage at the Vin pin, what is it?
Measure the 5V pin, what is it?
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The way you have it in your schematic isn't the same as how you have it wired up!

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Larry,
The Vin is reading 9.1 and the 5V pin on the sound card is at 4.99.
JR
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do you have something that supplies 5v over a usb cable?  like a small charger?  if that worked, it would rule out the powersupply question.  its more like a code thing, like hanging on a serial.available() or something
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I've now tried 3 different USB chargers. All fail. This is just driving me nuts. As soon as I plug it into the computer, it works.
JR
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sounds like a code thing.  can you post your code, and which versions of libraries you might be using.
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Could it be a code thing if it works when I have it powered by USB? It's works EVERY time if I connect the USB to my mac. If I power it off a DC supply, or a usb power supply, it fails. Every time. So I'm thinking it's not a code issue. But I'm willing to hear why I'm wrong. Could my mac be affecting how the code runs, even if the arduino app is not running? I will try connecting a bigger usb power supply. I've only tried the charger for an iphone, which is low power. I just ordered a 12 watt usb power supply. If that doesn't work, I'm throwing in the towel.
JR
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when you plug your arduino into the USB on your computer, you are doing 2 things: 1. giving it 5V power, 2. connecting it to a device that it can talk to.  your code is most likely trying to talk to the computer, and when there is no computer connected, it fails, and the program hangs.
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