USB port question

[benji]

i have a rf transmitter circuit beside my computer and this circuit needs power, so i thought why buying a battery as long as i have a usb port
very close ,,,,
i did read somwhere that the USB port can provide up to 500 mAmps ,,right?

well the problem is that i dunno how much current the rf transmitter needs,,,anyone??

does the usb port provide 5volts always ? or do i need to do anythin in windows or do program somthin?

thanks already for answers

[lkik]

why dont you get a cord and test it
the 2 wires on the sides of the plug are the power

[Private Reid]

A usb produces 5V by 500mA
Wiki has some usb stuff that i followed in making my various usb contraptions...

there is a negative, positive, 2 Data wires and a ground (usually uninsulated)

i don't recon it matters how much Amps the transmitter needs. buy a battery that will run the transmitter (make sure the battery is under 5V) and the usb port will just trickle charge the battery.

note: at 500mA an hour

[benji]

i was thinkin to power the transmitter from the usb directly,,without a battery, , possible?

[izua]

under usb specs, your device will have to enumerate. since this is not the case, you can sink about 100mA (50 units load) from a USB port without getting into trouble. Above 100mA your device will have to negociate higher power (up to 500mA per host). Most hosts don't care about it, but some will directly cut the current if this kind of surge is detected without beeing explicitly requested.

[benji]

Above 100mA your device will have to negociate higher power (up to 500mA per host). Most hosts don't care about it, but some will directly cut the current if this kind of surge is detected without beeing explicitly requested.

well how do i request it?

[Rebelgium]

Above 100mA your device will have to negociate higher power (up to 500mA per host). Most hosts don't care about it, but some will directly cut the current if this kind of surge is detected without beeing explicitly requested.

well how do i request it?

google and wikipedia will tell you

And to see howmuch current your transmitter draws, just measure it with a multimeter...

[benji]

google and wikipedia will tell you

And to see howmuch current your transmitter draws, just measure it with a multimeter...

i know i could do it, , its just time consuming cuz i dont have the transmitter in my hands to expirement with it,,
i was jus looking for quick data

[Admin]

well the problem is that i dunno how much current the rf transmitter needs,,,anyone??

Power it with a battery that you already own, and measure the current draw with a multimeter.