OK, I think I understand now. I don't think you need a digital potentiometer for that. Look at the IOIO-OTG schematic and identify Q1. It is a p-Channel FET responsible for the power supply on the VBUS line. When the IOIO is in device mode, its gate is left floating, and thus gets pulled up by R3 and the FET is not conducting.
When in host mode, the PIC will pull the gate low through Q2 and R3. According to the setting of R3, the gate voltage will vary, which can be used to put Q1 in linear mode, so that it acts as a resistor on VBUS and limits charging current. All you're missing, it being able to pull Q1's gate directly to GND in order to supply full current when your main supply is up. You can probably just extract a single wire from the leg of the chip, and connect it through an n-FET to GND, where the n-FET gate will be driven by a signal that tells you that your main supply is good. On Tue, Feb 11, 2014 at 2:23 AM, fabrio pellegrinetti <[email protected]>wrote: > Thanks for the answers. > > let me try to explain better...what I would need on the ioio is to control > the vbus with a digital potenziometer ioio embedded (controlled by java) > instead of the standard one because I need to mantain the usb connection > always active. > When the power line is present, I need to put via software the vbus at the > maximum value for the android recharge, while when the power line is off > the system needs to use the backup battery. In this case the vbus has to go > to the minimum in order to continue to use the usb connection. > > So, I need an hardware change on the ioio. > > > > > On Friday, February 7, 2014 11:09:30 PM UTC+1, Ytai wrote: > >> Such a FET already exists in the IOIO-OTG, however, this will also cause >> the USB connection to get dropped, which is I assume not what is desired in >> this case. >> On Feb 7, 2014 9:06 AM, "Nishant Sood" <[email protected]> wrote: >> >>> Fabrio, >>> >>> If you want to control charging of the android programmatically (in the >>> hardware it cuts off only when full charge automatically) then I would >>> suggest controlling the power going to the android controlled using a power >>> mosfet switched programmatically when you sense the system has gone to >>> battery backup >>> >>> >>> On Fri, Feb 7, 2014 at 10:28 PM, Ytai Ben-Tsvi <[email protected]> wrote: >>> >>>> I don't know if there's a programmatic way to disable charging on the >>>> Android. >>>> What you *can* do, however, is detect the power fault condition and >>>> put the phone to sleep. It should take very little current at this mode, >>>> assuming the battery was previously fully charged. >>>> >>>> >>>> On Fri, Feb 7, 2014 at 7:49 AM, fabrio pellegrinetti >>>> <[email protected]>wrote: >>>> >>>>> >>>>> hello to all. >>>>> during the development of my home automation project, I came across >>>>> the problem of the power supply of Android and ioio which must be >>>>> separated. >>>>> my board provide power supply of 14V 2A with a transformer 220V to >>>>> 14V and one backup battery of 1200mAh and 12V recharged from the >>>>> transformer. >>>>> When the the power line is off, the battery must supply power at the >>>>> ioio, but he mustn't to the android. >>>>> For now I use Y split cable power supply double USB A and one usb >>>>> micro. >>>>> >>>>> Micro usb connected to the android, first usb to ioio and second usb >>>>> to another standard android power supply. the poteziometer Vbus is set >>>>> to >>>>> minimum in accord to the usb debug survey. >>>>> Problem is when the system goes on battery the an amount of mA goes >>>>> to the standard android power supply and this reduce backup battery charge >>>>> What I would like is to be able to check the current Vbus, from java >>>>> code from a ioio embedded digital potenziometer. >>>>> >>>>> so when detect power failure, I can dinamically reduce Vbus current. >>>>> >>>>> thanks >>>>> best regards >>>>> >>>>> fabrio >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "ioio-users" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to [email protected]. >>>>> To post to this group, send email to [email protected]. >>>>> >>>>> Visit this group at http://groups.google.com/group/ioio-users. >>>>> For more options, visit https://groups.google.com/groups/opt_out. >>>>> >>>> >>>> -- >>>> You received this message because you are subscribed to a topic in the >>>> Google Groups "ioio-users" group. >>>> To unsubscribe from this topic, visit https://groups.google.com/d/ >>>> topic/ioio-users/s_NY9im_SVY/unsubscribe. >>>> To unsubscribe from this group and all its topics, send an email to >>>> [email protected]. >>>> To post to this group, send email to [email protected]. >>>> >>>> Visit this group at http://groups.google.com/group/ioio-users. >>>> For more options, visit https://groups.google.com/groups/opt_out. >>>> >>> >>> >>> >>> -- >>> *Thanks & Regards,* >>> >>> *Nishant Sood* >>> *--* >>> *CEO and Founder* >>> >>> *Winacro Innovation's Inc.* >>> *----------------------------------------* >>> *www.winacro.com <http://www.winacro.com>* >>> *----------------------------------------* >>> *Contact's:* >>> *Mobile: +91-8447476798* >>> *Phone: 0129-4176798* >>> *Email: [email protected]* >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "ioio-users" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To post to this group, send email to [email protected]. >>> >>> Visit this group at http://groups.google.com/group/ioio-users. >>> For more options, visit https://groups.google.com/groups/opt_out. >>> >> -- > You received this message because you are subscribed to the Google Groups > "ioio-users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/ioio-users. > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "ioio-users" group. 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