Cut power after shutdown

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Cut power after shutdown

Unread postby smuli » Sat Jul 21, 2018 4:04 am

Hi,

I'm working on a project where an Odroid C2 is part of a machine. The customer shuts down the power of that machine when it is not needed anymore.
To not loose any data I added the UPS3 module for a clean shutdown. After main power off the C2 initiates the system shutdown and then the power to the C2 should be cut to not drain the battery. But when the power returns the C2 should be powered on again.

So I thought of a simple solution where I unsolder the on/off dip-switch at the UPS and connect them to a bistable relay.
Please find attached my simple plan.

The problem is that I can get a 5v version without a problem but the 4.5v or the 3v versions I have to buy in bulk at 500pcs :)
And as far as I know the GPIO only sends out 3.3v for a one shot and not 5v.

Has anyone a better solution for such a case?

Kind regards
Smuli
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Re: Cut power after shutdown

Unread postby odroid » Sat Jul 21, 2018 9:27 am

Bistable relay is a good idea.
I think you can add a level-shifter something like this.
https://www.ebay.com/itm/5Sets-4-Channe ... 2151474158

Another concern,
Normally GPIO output current is only a few milliampere.
What is the minimum required current to toggle the latch in the Bistable relay?
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Re: Cut power after shutdown

Unread postby smuli » Sat Jul 21, 2018 11:40 am

Thx for your reply.

If I'm right that should be 36mA

Please have a look at http://www.produktinfo.conrad.com/daten ... S_5VDC.pdf
Double-winding Latching, DPDT Relays.

Do you have a better idea how to solve the whole thing?
The best would have been if Hardkernel had provided a killswitch instead of draining the battery - but for now I have to solve this in another way :)

Kind regards
Smuli
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Re: Cut power after shutdown

Unread postby odroid » Mon Jul 23, 2018 9:14 am

C2 consumes around 40~50mA in the power-off state. The difference is not so big.
So you can consider this much simpler approach probably.
https://wiki.odroid.com/odroid-c2/appli ... key_wakeup
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Re: Cut power after shutdown

Unread postby smuli » Tue Jul 24, 2018 11:46 pm

Thx for your suggestion. But I think I will stick with the first idea. Can you please tell me the output in mA from the GPIO pins on the Odroid C2 or where I could find that? I searched through the wiki and the forum and couldn't find it.

Thx in advance.
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Re: Cut power after shutdown

Unread postby odroid » Wed Jul 25, 2018 12:09 pm

GPIO can drive up to 4mA.
Check the S905 datasheet page 38.
https://www.hardkernel.com/main/product ... &tab_idx=2
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