how to make the usb interface on pi as output

[murny_shah]

hello fellas,

i'm in the middle of doing my final year project about pir sensor... my project is, to switch on the light when motion is detected... i want to use desktop led lamp as the output...as you all know, the desktop led lamp is using usb in order to swtich on... i want to use the usb interface on the raspberry pi to connect it with my desktop led lamp...how am i gonna do that?? is there any suggestion or mybe if there any python coding for that,can you all share it for me... i'll appreciate your help...

thank u...

[ShiftPlusOne]

Please don't spam the same topic across the forum. Thanks.

[Burngate]

...as you all know, ...

Don't make too many assumptions!

I don't know about your lamp, but others I've come across don't have any control - if there's power on the USB plug, the lamp is lit.
As the Pi's USB sockets are always powered*, you can't control the lamp that way. You'll need to put some electronics into the lamp, and drive it from a GPIO


*not quite true - on the B+, the power goes through a switch-chip, and that's got an enable on it, that comes from the 9514 USB/LAN chip.
But you probably didn't want to know that.

[Tarcas]

as you all know, the desktop led lamp is using usb in order to swtich on...

How exactly was I supposed to know that?

Does the USB connection from the lamp actually have logic on it to switch it on and off over USB, or is it just a USB-powered lamp like Burngate mentioned?

If it has logic on it, check the datasheet and send whatever signal it's expecting to turn off and on. If not, I'd use a GPIO pin to switch a relay or transistor which controls the lamp instead. You'd obviously have to tap into the power wire of the lamp's cord if this is the case.

[hippy]

on the B+, the power goes through a switch-chip, and that's got an enable on it, that comes from the 9514 USB/LAN chip.

Do you have a link to details on that as the circuit diagram I have for the B+ doesn't show it. Perhaps I haven't got the latest circuit diagram?

[Burngate]

Do you have a link to details on that as the circuit diagram I have for the B+ doesn't show it. Perhaps I haven't got the latest circuit diagram?

Sorry, don't have a link - I prodded around with my meter, used my skill and judgement (AKA guessed) and came up with this - I can't guarantee the accuracy!

USBpower.png (5.39 KiB) Viewed 8389 times

Note: no component values, and the diode might be reversed!

[B.Goode]

hello fellas,

So you don't want to hear from any female readers who might have information for you?

(Or maybe 'fellas' is now gender-neutral, like 'actor'?)

To the point: the power lines in the RPi usb sockets are not themselves (trivially) programmable. Maybe you could take that constant power feed to a chip like those used in motor-control H-bridge circuits, and switch that on and off via a programmable gpio pin? But if this is your final-year project that's as helpful as I am going to be...

[mahjongg]

Do you have a link to details on that as the circuit diagram I have for the B+ doesn't show it. Perhaps I haven't got the latest circuit diagram?

Sorry, don't have a link - I prodded around with my meter, used my skill and judgement (AKA guessed) and came up with this - I can't guarantee the accuracy!

USBpower.png

Note: no component values, and the diode might be reversed!

I can confirm the correctness of the schematic, and can add some values.
Diode is one halve BAV99 with cathode on enable pin, FET = DMG1012T,
resistors from left to right:
1K8 Pullup R48
100K R47 over diode
R50 and R4 both 39K to gnd and to drain FET
R6 100 gate pulldown.
capacitors:
220nF C106 on enable pin, and also on Vin and Vout.
IC U13 = AP2553W6

also the fault signal from/to the LAN9514 is called "USB_OVC_N", and can both be used to sense a fault condition AND to force USB power off! (something I missed at first, but for someone insisting the USB power could be turned off).
The signal goes to pin 14 of the LAN9514.