Arduino Diy pH probe - Page 2 - The Planted Tank Forum
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post #16 of 22 (permalink) Old 01-28-2013, 11:56 PM
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Originally Posted by Jeffww View Post
Or alternatively is there a way to split the 5V into multiple connection points so I can run my LCD and my probe.

edit:

I've read that I can split it through a parallel circuit with any number of devices whose total draw is less than 1A so that I don't fry my components. Does that sound right?
As mentioned, you can split your 5V line along a breadboard/protoboard and then use some resistors to power both your LCD and pH probe.

Alternatively, you could always just write one pin high so that it's at 5V (less efficient).

As a side note, the Arduino can only provide 500 mA maximum. There are other restrictions on certain pins (i.e. total of X to Y can only be 200 mA, etc). The Arduino website has the specifications for these current draw limitations.

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post #17 of 22 (permalink) Old 01-29-2013, 03:02 AM Thread Starter
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Really? I thought it was a 500ma max if it draws from a computer USB and 900ma if it took from a 9V adapter. Or rather, it would draw since there is no regulator as much as it could until something broke with 900ma being the general safety limit either in built to some arduino or just as a precaution.

edit: also why would I need resistors to bring down the current for the LCD? Why can't I directly wire them in parallel.

Last edited by Jeffww; 01-29-2013 at 03:18 AM. Reason: why
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post #18 of 22 (permalink) Old 01-29-2013, 03:54 AM
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It is definitely 500 mA maximum if drawn from USB. I am not sure what the maximum total current draw is when using an AC to DC adapter.

Each pin can supply a maximum of 40-50 mA, depending on which board revision you have.

To be honest, if you find yourself needing to draw more than 500 mA, you should be using a separate power supply anyway.

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post #19 of 22 (permalink) Old 01-29-2013, 06:22 AM Thread Starter
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That being said, it shouldn't really take that much current to run just a probe (a couple of ma at most) and an LCD though....So dividing the 5V pin seems pretty safe.
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post #20 of 22 (permalink) Old 02-03-2013, 11:13 PM Thread Starter
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So I've got the pH displaying on the LCD at this point, working on button controls. However, I'm encountering some really weird problems. When I run the set up on its own directly from the outlet power it gets crazy pH fluctations. It's only stable when it's attached to my computer. I'm starting to think that my adapter is messed up.
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post #21 of 22 (permalink) Old 02-03-2013, 11:23 PM
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too much or not enough current maybe. Check on how much voltage & current for optimal function.

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post #22 of 22 (permalink) Old 02-07-2013, 03:45 AM Thread Starter
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Will do. Although I wonder why it would work fine connected to the pc but not to the wall?
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