Re: [Gumstix-users] I/O-Pin-Level (in / out) and getting power (3,3V) out of gumstix ?

[Brad M. <bmi...@xm...>]

Dave,

I should have been paying better attention to the original thread... I 
actually need this circuit turned around if possible :)

I don't care about power consumption since I am just prototyping... but 
what I want is the simplest circuit to power a 3.3v external device 
(bluetooth class 1 module) using the gumstix 5v supply, perhaps switched 
on & off from a gpio if that doesn't complicate it.

Brad

Dave Hylands wrote:
> Hi Brad,
> 
> 
>>>You could use a resistor divider to convert from 5v to 3.3v
>>
>>I am just a menace to anything other than software (maybe software too),
>>but could you give me an idea of how to choose the resistors for this? I
>>see one from the 3.3v lead to 5v and one pulling the 3.3v lead down to
>>ground (I think). Do people actually build these out of two resistors or
>>just buy an IC?
> 
> 
> It depends on whether you care about current consumption or not.
> 
> Using two resistors will work (in the 5v to 3.3v direction), but using
> an IC will draw less current. If you're using a battery it might make
> a difference (it would also depend on how many lines you're doing this
> with).
> 
> I mentioned in my previous email that picking a 6.8k and 3.3k
> resistors would work fine. This gives 10.1k at 5v which would draw
> half a milliamp when the 5v signal is at 5v and won't draw any current
> when the 5v signal is at 0v.
> 
> You woulkd connect them something like this:
> 
> +--5v signal
> |
> |
> 3.3k resistor
> |
> |
> +--- goes to gumstix GPIO pin
> |
> |
> 6.8k resistor
> |
> |
> +-- goes to 5v ground and gumstix ground
> 
> You could also use a RoboStix when it's available since it will have
> 5v I/O> then you'd just need to write some software to send stuff back
> and forth.
>