Power GPS from PS/2 port?

[deepo]

Hi!

I'd like to power my Garmin eTrex Vista GPS receiver from the PS/2 port, and at the same time connect it to a serial port to allow serial communication without running the Vista on batteries.

The Vista specifications says that power consumption is at most 0.5 W and it operates at 3 V, i.e. max 150 mA at 3 V. Users report a max of 60-80 mA.

My plan is to take +5V and GND from the PS/2 port, connect a LM317 voltage regulator to obtain a 3V output. (R1=240, R2=330, Vout=2.97 V).

Like this example: **broken link removed** **broken link removed**

Is the PS/2 port capable of powering such a load?

Any comment is most welcome.

/Mogens

 

[ChrisP]

In theory, yes. There are several external USB and/or parallel port devices offered that use the keyboard port for their power source, especially higher-current USB2.0 devices when used on a pre-USB2.0 PC. For example, I have an older parallel port Camera-Mate card reader that uses this power scheme.

However, you should be aware that this scheme also has its drawbacks. I have seen some systems that would not start with the device connected, but would work normally if the device were connected after startup. It should also be recognized that the actual current available at the keyboard port (do not use the mouse port for this unless there is no mouse connected) will depend upon the designs of the mainboard and the power supply. If both of those components are at the low end of their tolerance ranges, that particular combination may not provide adequate current.

 

[Someone Electro]

Why don't you use a transformer? :?

 

[Exo]

IBM PS/2 Specification says max 100mA load per port.
In practice the power pins of a PS/2 port on most motherboards are directly connected to the main 5V rail of the pc, and thus capable of powering larger loads.

stick to the IBM specification or not. It's up to you

 

[deepo]

Why don't you use a transformer? :?

I want to use my GPS without the need for a power socket. I want to be able to use my GPS outdoors with a notebook PC as long as it's battery allows.

/Mogens