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Power-up settings

990 Views - Created 11/11/2017

11/11/2017

Posted by:
georgecomber

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Location:
Ireland

Hi,

I am using the Pi plus onewire board to turn on and off  machines in my factory using MAXIM DS2413 switches.

When the pi is shut down, the switches maintain their state, I presume because the AB board is still powered.

The problem is if the power is disconected or interuppted, the switches power up all switched on and everything turns on.

Is there a way of setting the power-up states or protecting against this with hardware?

It strikes me that not being able to control the power-up states of the switches rendered them pretty useless.

Thank you,

George Comber

11/11/2017

Posted by:
andrew

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Location:
United Kingdom

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Hi

According to the datasheet for the DS2413 on page 4 the power on default is set to off but as the outputs are open drain I expect with your circuit that is causing the switches to go high.  It doesn't look like it is possible to change the default startup state so the only thing you could do would be to put a logic inverter in between the DS2413 outputs and your hardware so they would then default to an off state when powered up.

AB Electronics UK Tech Support

12/11/2017

Posted by:
georgecomber

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Location:
Ireland

Thank you so much for the quick reply. I can see now on page 4  about the power up condition.

I read it a hundred times myself  and could not see that.

Yes, I am using the switches with pull up resistors connected to the gates of some 2N7000 mosfets so when the switch is off (not conducting) the fets turn the relays on. I will put a second set of mosfets after them  to reverse the signal.

It will also mean that writing a "1" will turn the relays on because , although the datasheet seems to say that writing a "1" will turn off the switch, the owfs implementation seems to work the other way around.

Thanks again for the support.

George

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