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## Re: [Gumstix-users] Power Question

 Re: [Gumstix-users] Power Question From: Dave Hylands - 2006-05-04 22:25:34 ```Hi Vaibhav, > I was working with the Robostix today, and using the General I/O pins. W= hen > I set the I/O pin to 1, and use it across a 2k ohm and 1k ohm resistor, t= o > drop the VDD to 2.7V, the I/O pin voltage drops from 3.9V to 0.3V . ANy > idea why this would happen, and how we can get around this problem? It > seems that any load on that pin drops the voltage down. I don't know what your load is, but let's say it draws 50ma across 2.7v. V =3D IR, so R =3D V/I =3D 54 ohms effectively. Now look at your resistors. You've got a 2k in parallel with a 54 ohm, which translates to basically a 53 ohm resistor, in series with a 1k resistor. So the new voltage will now be 53/1053 * 5 =3D 0.25v. In order to keep the voltage up, you'd need to use 1 ohm and 2 ohms resistors, but they would try and draw 1.6 amps which is way above what the GPIO pin is spec'd for :) You'll need to use a voltage regulator to provide power to your external device. Resistor dividers are really only appropriate going into high impedance inputs (like an input signal) and are generally not appropriate when a load is involved. -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/ ```

 [Gumstix-users] Power Question From: Vaibhav Sarihan - 2006-05-04 22:10:15 Attachments: Message as HTML ``` Hi, I was working with the Robostix today, and using the General I/O pins. Whe= n I set the I/O pin to 1, and use it across a 2k ohm and 1k ohm resistor, to drop the VDD to 2.7V, the I/O pin voltage drops from 3.9V to 0.3V. ANy ide= a why this would happen, and how we can get around this problem? It seems that any load on that pin drops the voltage down. THanks, Vaibhav ```
 Re: [Gumstix-users] Power Question From: Dave Hylands - 2006-05-04 22:25:34 ```Hi Vaibhav, > I was working with the Robostix today, and using the General I/O pins. W= hen > I set the I/O pin to 1, and use it across a 2k ohm and 1k ohm resistor, t= o > drop the VDD to 2.7V, the I/O pin voltage drops from 3.9V to 0.3V . ANy > idea why this would happen, and how we can get around this problem? It > seems that any load on that pin drops the voltage down. I don't know what your load is, but let's say it draws 50ma across 2.7v. V =3D IR, so R =3D V/I =3D 54 ohms effectively. Now look at your resistors. You've got a 2k in parallel with a 54 ohm, which translates to basically a 53 ohm resistor, in series with a 1k resistor. So the new voltage will now be 53/1053 * 5 =3D 0.25v. In order to keep the voltage up, you'd need to use 1 ohm and 2 ohms resistors, but they would try and draw 1.6 amps which is way above what the GPIO pin is spec'd for :) You'll need to use a voltage regulator to provide power to your external device. Resistor dividers are really only appropriate going into high impedance inputs (like an input signal) and are generally not appropriate when a load is involved. -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/ ```