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TassyJim

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Joined: 07/08/2011
Location: Australia
Posts: 6273

Posted: 10:32pm 30 Jul 2015

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I took a few measurement on my Explore64 and 7 inch display.
All readings are on the 5V supply with USB disconnected.

Explore64 without display 77mA
Display running with 10% brightness (includes explore64 load) 210mA
Display running with 100% brightness (includes explore64 load) 510mA

Jim

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Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 9603

Posted: 12:55am 31 Jul 2015

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Yeah, that sounds about right to me. She's a thirsty girl, the 7" one!

Smoke makes things work. When the smoke gets out, it stops!

MMAndy
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Joined: 16/07/2015
Location: United States
Posts: 91

Posted: 02:40am 31 Jul 2015

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@TassyJim

Quote Display running with 100% brightness (includes explore64 load) 510mA

That includes the keyboard running at 100 ma. ?

Is there any perceived difference of having the TFT brightness at 50% than at 100% ?Edited by MMAndy 2015-08-01

TassyJim

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Location: Australia
Posts: 6273

Posted: 11:50am 31 Jul 2015

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MMAndy said

That includes the keyboard running at 100 ma. ?

No keyboard or any other peripherals attached.

Quote
Is there any perceived difference of having the TFT brightness at 50% than at 100% ?

Yes, the change in the display is gradual over the full range.
Geoff's demo stopped at 10% which is why I didn't try 0% (hard to to anything at that level but useful in real life as a 'screen saver'

Jim

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MMAndy
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Joined: 16/07/2015
Location: United States
Posts: 91

Posted: 01:09pm 31 Jul 2015

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If I could get ~ 0.5 amps with 50% brightness for normal operation that would be great! A portable MM+ Explore64 computer with TFT 7" LCD display and keyboard "could" run for 28 hours or for 3.5 eight hour days from a portable USB 20,000 mAh power/charger/battery Lithium pack.

USB (Lithium) battery/charger packs are quoted in mAh but that's a "marketing"
number which is very deceiving. The mAh is the current available from the nominal
voltage of the Lithium pack around 3.7 V. The USB pack will also need to step-up
the voltage to 5V. A crude calculation is most USB packs are least 70% efficient.
So 20,000 mAh pack will only produce about 14,000 mAh.
(1 amp is 14 hours and 1/2 amp is 28 hrs) <--- this value will need to be tested and checked on a running unit.

Edited by MMAndy 2015-08-01

palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1991

Posted: 01:30pm 31 Jul 2015

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I would have liked to see an on board 5 volt regulator, I think it would make the choice of power supplies easier. I guess I could run off more than 5 volts but the 3.3v
regulator gets very hot and the 5V. out pin would no longer be 5V.
Paul.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

TassyJim

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Location: Australia
Posts: 6273

Posted: 02:47pm 31 Jul 2015

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My favorite power supply is a (cheap Chinese) 5V switch-mode regulator rated at 3 amps.
I limit them to 2 amps and I usually have a 12V battery backed supply handy.

I fitted the diode in the explore64 to stop backfeeding the USB. I think I will also isolate the USB from the display in case I try and feed the lot from USB.

My adapter board is veroboard so mods are easy.

Jim

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