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I am trying to have a single soft button to power on my arduino, and then have it power down if certain conditions are met.
My plan is to have a BC639 transistor to control the power to the arduino, and in my sketch, have an output go high on startup (pin smiley-cool, and to power on the arduno I would hold a button down untill the arduno had powered up (indicated by an led on pin 13), I could then set pin 8 to low which would stop current going to the BC639 and shutdown the arduino. Would this work???

Thanks

Jim
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To control power supply line, you need to use PNP transistor, set pin out low to hold the transistor to on.
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Thanks Bill,

I don't know much about transitors, can you recomend a PNP transistor?

Would I be correct in assuming that a PNP transistor with a higher current capacity would draw more current when not in use?
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Would I be correct in assuming that a PNP transistor with a higher current capacity would draw more current when not in use?
No you would not be correct.
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This is the circuit that use P-MOSFET to switch the supply line
http://www.edn.com/file/24877-Figure_2.pdf
http://www.edn.com/design/analog/4362161/Transistor-latch-improves-on-off-circuitry
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Nick Gammon in his Arduino power saving tome mentions that the TV B-gone product does the various IR controls, and then puts itself to deep sleep, and the button you press is the reset button which powers it back on.  Now this will use some amount of power even when it is sleeping, but in the grand scheme of things, it may be enough for your purposes.  Here is the article: http://www.gammon.com.au/forum/?id=11497

Here is the TV-B-Gone kit that ladyada sells, but I'm not sure if the source is available: http://www.ladyada.net/make/tvbgone
« Last Edit: February 25, 2013, 11:36:59 am by MichaelMeissner » Logged

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Thanks for all the info guys,

What is the role of the DC/DC converter?

Also is the value of Q1 critial, or will any p channel mosfet be ok?
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What is the role of the DC/DC converter?

Also is the value of Q1 critial, or will any p channel mosfet be ok?

the role of the DC/DC converter is like the voltage regulator.

Best get the Logic Level p channel MOSFET for the Q1 with spec for your max voltage and current need.
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Hmm, would a bistable (latching) relay be a good idea? A button activates it, a circuit is closed and the power to the Arduino starts flowing. Arduino does its thing and when it's done it turns itself off by pulling its own plug.
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Hmm, would a bistable (latching) relay be a good idea? A button activates it, a circuit is closed and the power to the Arduino starts flowing. Arduino does its thing and when it's done it turns itself off by pulling its own plug.

I've used such a method on a couple of projects using a single coil latching 5vdc relay.

http://img25.imageshack.us/img25/563/08miq7.jpg

Lefty
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If it will only be off for a few days, you can effectively put it to sleep instead as mentioned above.
The power consumption will not be significant compared to the time it is on drawing 40ma or whatever.
The advantage of this method is that there is no additional hardware needed.
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Thanks for the info everyone,

I'd like my project to run from a 9v pp3 battery, and be in standby /  off for around 99% of it's time and get one years battery live, so I think standby is not going to be an option.
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I think you are right.  On the other hand, some quick math.  50ua x 100 since it's sleeping 100x as much = 5ma.  This is only a small portion of the 20-50ma required when awake.  In theory if it works with 0 power 99% of the time, it will only use 10% more sleeping.  Do you follow me?

At 50ma on 1% of the time that is about 10mah per day or 3AH per year.  A pp3 battery is only about 300mAh.  See the problem?
« Last Edit: February 26, 2013, 09:11:29 am by sbright33 » Logged

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